MINERALS. (continued 2)

Few precious stones are more beautiful than opals. Their elegant play of colours, brilliant blue, green, red, and yellow, variously modified, has procured for 64them a distinguished rank among gems. Notwithstanding this, they are but ill suited to the purposes of jewellery, on account of their softness, their great frangibility, and their sometimes splitting on a sudden change of temperature. They are usually set without bottoms; but sometimes with a black bottom, and sometimes with a foil of red, blue, or gold colour. Their value is such that a fine oriental opal is considered worth about twice as much as an oriental sapphire of the same size. By the Turks they are so peculiarly esteemed, that a fine opal of moderate size has sometimes been sold at the price of a diamond. The esteem in which they were held among the ancient Romans was such, that Nonius, the Roman senator, is stated to have preferred banishment to parting with a favourite opal which Mark Antony was anxious to possess.

In the abbey of St. Denys, near Paris, there was formerly a curious ancient opal which was green on the outside, and, when viewed against the light, exhibited a fine ruby colour: and in the Imperial Cabinet at Vienna, there are two pieces of opal, from the mines in Hungary, one of which is about five inches long, and 2½ inches broad; and the other the size and shape of a hen’s egg. Both these stones exhibit a very rich and splendid play of colours.

In the purchasing of opals great caution is requisite, as fine glass pastes have not unfrequently been substituted for them, and sold at enormous prices.

103. Hydrophanous Opal, or Oculus Mundi, is a kind of opal, the distinguishing characteristic of which is, that it gradually becomes transparent, and exhibits a beautiful play of colour after being immersed in water. It is either of a whitish brown, yellowish green, milky grey, or yellow colour, and opaque; and, when touched by the tongue, adheres to it.

The name of oculus mundi has been given to these stones from an internal luminous spot, which changes 65its position according to the direction in which they are held to the light. The countries in which they are chiefly found are Hungary and Iceland.

They are sometimes set in rings; and the prices at which they were formerly valued were, in the highest degree, unaccountable and absurd. At present their value is considerably lower, though they are still in great request as objects of curiosity. The phenomenon of their becoming transparent in water is supposed to be occasioned by that fluid soaking through their whole substance, in the same manner as the transparency of paper is occasioned by immersing it in oil. An hydrophanous opal weighing 27½ grains was kept four minutes in water, and, on being taken out, weighed 32½ grains, having received in this short period an augmentation of five grains, or more than one sixth part of its whole weight. When taken from the water, these stones as they dry become again opaque.

To preserve them in beauty and perfection, care should be taken not to immerse them in any but pure water, and to take them out as soon as they have acquired their full transparency. If these precautions be neglected, the pores will soon become filled with earthy particles: the stones will cease to exhibit their peculiar property, and will ever afterwards continue opaque.

104. Common Opal is a semi-transparent kind of opal, which does not exhibit any changeable refraction of colour. It is found in Germany, France, Italy, and other countries of the Continent, and is employed for brooches and other ornaments. A green-coloured Saxon variety is sometimes cut into ring-stones.

66106. Wood Opal appears to be wood that, by some extraordinary operation of nature, has been converted into opal. Some specimens exhibit, very beautifully, the ligneous texture. This kind of opal is chiefly cut into plates for the tops and bottoms of snuff-boxes. It is found in alluvial land in some parts of Germany and Hungary. Several years ago the trunk of a tree, penetrated with opal, and so heavy that eight oxen were requisite to draw it, was found in Hungary.

PITCHSTONE FAMILY.

This substance has been used for various purposes. It is possible to cut and polish it; but its brittleness and frangibility are so great, that, without much care, it will fly into pieces during the working. The reflectors of telescopes are sometimes formed of it. In Mexico and Peru obsidian is cut into mirrors; and the inhabitants of those countries used formerly to manufacture it into knives and other cutting instruments. Hernandez says that he saw more than a hundred of these knives made in an hour. Cortez, in a letter to the Emperor Charles the Fifth, relates that he saw razors that had been formed of obsidian. The natives of Easter and Ascension Islands use this substance for cutting instruments; and also for pointing their lances and spears, and, in place of flint, for striking fire with. According to the account that has been given by Pliny, the ancients sometimes formed obsidian into mirrors, and ornamental articles of different kinds. The Danish lapidaries, who obtain considerable quantities of it from Iceland, cut it into snuff-boxes, ring-stones, and ear-pendants.

Obsidian is found near Mount Hecla, and in other parts of Iceland. Sir George Mackenzie, during his journey through that island, observed an immense mass of this substance, which appeared to him to have been 67part of a stream that had flowed from a volcano. It is also found in Sicily, and several other islands of the Mediterranean; and in nearly all parts of the world where there are volcanoes.

From the texture of this mineral, which is chiefly brought from the neighbourhood of volcanoes, some persons have imagined it to be asbestos decomposed by the action of fire. Its lightness is such that, placed in water, it will float.

To mechanics and other artists pumice stone is a very useful mineral. It is employed for cleansing and smoothing the surface of wood, leather, metal, stones, glass, and other substances; and it is used by parchment-makers, curriers, and hat-makers. Hence it forms a considerable article of trade: and is exported from the Lipari Islands, in great quantities, to the different countries of Europe. Sailors in the Mediterranean rub their beards off with pumice, instead of shaving. On account of its porosity, it is used in Teneriffe as a filtering stone. It forms a pernicious ingredient in some kinds of tooth powder; and in Italy is ground and used instead of sand, in the making of mortar. Pumice occurs in Ireland, along with obsidian (107); and it abounds in several islands of the Grecian Archipelago.

AZURE STONE FAMILY.

109. LAPIS LAZULI, AZURE STONE, or LAZULITE, is a mineral of azure-blue colour in various shades, and generally accompanied with white or clouded spots, and also with pyrites (236), which have the appearance of golden veins or spots. Its texture is earthy, and fracture uneven. It is opaque, or nearly so, and, in some parts, is sufficiently hard to strike fire with steel. We are not informed that lapis lazuli is otherwise found than in shapeless masses or lumps.

68About fifty years ago this stone was an article much in fashion for various ornamental parts of dress. Being capable of very high polish, it was cut into beads, stones for rings, bracelets, and necklaces. It was also cut into ornamental vases, small statues, and the tops and bottoms of snuff-boxes; but of late it has been almost wholly out of use for these purposes. Before the French Revolution it was imported, to considerable extent, into that country from the Persian Gulf for the inlaying of richly-decorated altars; and its value was appreciated according to the proportion of its yellow spots or veins: these, by many persons, were erroneously considered to be of gold.

The most important purpose to which lapis lazuli is now applied is in the manufacturing of the beautiful and brilliant blue colour so much esteemed by painters, called ultramarine. For the making of this, such pieces are selected as contain the greatest proportion of blue substance, and consequently the least yellow or white. These are burned or calcined, reduced to a fine powder, made into a paste with wax, linseed oil, and resinous matters of different kinds, and afterwards separated by washing. The powder that is left in this operation, which requires much time and great attention to perform, is ultramarine.

There are few colours so little susceptible of change from the effects of time as ultramarine: the consequence of this has been that, as several of the ancient painters introduced it for the representation of blue drapery, their pictures, in many instances, are now devoid of harmony, as this colour alone has stood, whilst all the others have changed.

Lapis lazuli is principally brought from Persia, Natolia, and China; but it is also found in Siberia and Tartary. In Europe it has been discovered only in Germany, and among the ruins of Rome.

A coarse imitation of it is sometimes made by throwing copper filings into blue enamel whilst in a melted state.

69 FELSPAR FAMILY.

It is found in a massive state, disseminated or crystallized in four, six, and ten-sided prisms; will strike fire with steel, and is sometimes opaque and coloured, sometimes transparent and whitish.

The name of felspar is derived from the German language, and signifies spar of the fields. It is a very common substance, and constitutes a principal part of many of the highest mountains of the world. When exposed to weather, it gradually acquires an earthy appearance, and at length passes into porcelain clay (118).

Felspar is of great use in the manufacture of the finer kinds of earthenware. Of the two substances which chiefly compose the porcelain of China, one called petunzé is a whitish laminar kind of felspar. This mineral is used in the celebrated porcelain that is manufactured at Sevres, near Paris, for the purpose of giving to it a white and transparent appearance. Previously to being used, it is pulverized, made into a paste, and suffered to dry. It is sometimes applied to the surface of ornamental vases in the form of enamel.

111. Amazon Stone is a green variety of felspar, which is found in small rolled pieces on the bank of the river of Amazons, in South America, whence it has its name. It is susceptible of a beautiful polish, and is often cut into ring-stones, brooches, and the tops of snuff-boxes. Lapidaries consider it to be most estimable when accompanied by mica, which gives it a kind of speckled perlaceous appearance.

112. LABRADOR FELSPAR is a very beautiful stone, of smoky grey colour, intermingled with veins and shades of blue, green, and golden yellow, exhibiting a brilliant play of 70colours, according to the position with respect to the light in which it is held.

The original discovery of this singular mineral was by the Moravian missionaries, on the island of St. Paul, near the coast of Labrador; but it has since been found in various parts of Norway and Siberia. Persons who have passed in boats along the rivers of Labrador, have described the extremely brilliant and beautiful appearance which the rocks of this substance frequently exhibit in shallow places, at the bottom of the water. The visitors of the late Leverian Museum will, no doubt, recollect a remarkably fine mass of Labrador felspar, the surface of which was polished, and exhibited some of the most splendid and beautiful colours that can be imagined. It was considered to have been the most capital specimen that was ever brought to England.

This mineral, on account of its hardness, its brilliancy, and its capability of receiving a high polish, is in considerable estimation among lapidaries for different kinds of ornamental work, particularly for the tops and bottoms of snuff-boxes, for brooches, and necklaces.

The translucent varieties of this stone, when viewed in a certain direction, sometimes exhibit a pearly and silvery play of colour. These are valued by jewellers, who cut them into a semi-globular form, and sell them under the name of moonstone. Those specimens are considered most estimable which, when cut in a very low oval, present the silvery spot in the centre of the stone. They are generally used for rings and brooches; and when set round with diamonds, their pearly lustre exhibits a striking and agreeable contrast with the brilliancy of that gem.

71Adularia is said to have been first discovered by an Italian mineralogist, near Mount St. Gothard, in Switzerland. He named it Adularia felspar, in the belief that the mountain on which he had found it was named Adula. This, however, was not the case; for Mount Adula is at some distance from St. Gothard, in the Grisons. This mineral has since been found in the granite of the island of Arran, in France, and Germany. The finest specimens are brought from Ceylon.

ORDER II.–SOFT STONES.

(Those which will not scratch Glass.)

CLAY FAMILY.

114. Clay is a mixture of alumine (33) and silex (38), and is too well known to require much description.

It is opaque, has an earthy texture, is about twice as heavy as water, when moistened is very ductile, adheres slightly to the tongue; and with its peculiar smell (called clayey) every one is acquainted.

It is the peculiar quality of this substance to become so hard by heat that it will even strike fire with steel. The ductility of clay, and its property of thus hardening in the fire, have rendered it an article of indispensable utility to mankind in all civilized countries. It is formed into eating vessels of almost every description; plates, dishes, cups, basins, bowls, and pans for keeping provisions in. For these almost any kind of clay may be advantageously used; but it is necessary to mix it with sand, for the purpose of rendering the vessels 72that are made of it more firm and strong. Those that are applied to culinary, and other uses in which it is requisite for them not to be penetrable by water, are covered with a glazing. This glazing, for coarse ware, is sometimes made with lead, and sometimes by throwing a certain portion of salt into the furnace. In the formation of the better kinds of earthenware, the clay is made into a paste with water, moulded into the requisite shape upon an horizontal wheel, the inside being formed by one hand of the potter, and the outside by the other, as the wheel turns round. When the pieces have been baked, they are dipped into a glazing mixture, consisting of white lead, ground flints, and water, and are exposed a second time to the fire. The different colours of earthenware are obtained by means of various kinds of metallic oxides (21).

The coarser kinds of clay are manufactured into bricks for the building of houses, and tiles for the covering and paving of them. These are formed in moulds of the requisite shape, afterwards dried for some time in the sun, and finally piled in kilns, and there baked to a proper degree of hardness. The earth for bricks ought to be sufficiently fine, free from pebbles, and not too sandy, which would render them heavy and brittle; nor ought it to be entirely free from sand, as this would make them crack in drying.

Clay is a substance of inestimable value for forming the bottoms of ponds, and the bottoms and sides of canals and reservoirs, to prevent the water from draining away. It also composes, in a great measure, those tenacious earths called arable soils. What is peculiarly denominated clay land is known by its holding water, and not soon drying when wetted. Such land requires much labour from the husbandman, before it can be sufficiently pulverized, or brought to a fit state for being productive of corn or grass.

116. Pipe Clay is a fine and yellowish white variety of common clay. It is very plastic, adheres strongly to 73the tongue; and, in a strong heat, is hardened, and rendered perfectly white.

It is of this clay that tobacco pipes are made, by the simple process of casting them in moulds, forming a hole through the stems by means of a wire, generally dipping the small end into some glazing material, and then baking them. Pipe clay is also formed into oblong pieces, dried, and employed for cleaning white woollen cloths, and for various purposes of domestic utility. It is likewise the basis of the yellow, of what is called Queen’s ware pottery. This is glazed in a manner somewhat different from that of common pottery. The glazing mixture consists of a certain proportion of carbonat of lead (239), ground flint, and flint glass, worked with water to the thickness of cream. The ware, before it is glazed, is baked, and thus acquires the property of strongly imbibing moisture. It is then dipped into the above composition; exposed a second time to the fire, by which the glaze it has imbibed is melted. A thin glossy coat is thus formed upon its surface, which is more or less yellow, according to the greater or less proportion of lead that has been used.

117. LOAM is a yellowish or brownish kind of clay; sometimes containing a considerable proportion of sand. It occurs in immense beds, and is found in almost every part of the world.

This substance, when mixed with straw or hair, to prevent it from cracking, is extensively used for the building of what are called mud cottages or houses. These are generally reared on a foundation of stone, or brickwork, to secure them from injury by the moisture of the earth. It is said to be the most advantageous practice to form the loam into bricks, and to dry these in the shade, and afterwards in the sun. The use of such bricks is of great antiquity. We are informed that the ancient city of Damascus, and even the walls of Babylon, were constructed of bricks made of loam.

It is known from the other clays by the fineness of its particles, its soiling the fingers much when handled, and its fine but meagre feel.

The usual distinction betwixt earthen ware and porcelain is, that the former is opaque, and the latter semi-transparent. In the manufacture of porcelain the clay is sometimes used alone, and sometimes intermixed with other earths, or with felspar (110). The earliest manufacture of porcelain is supposed to have been that in China and Japan. The quantity produced in China must formerly have been extremely great; as not only a considerable portion of the eastern parts of the world, but almost the whole of Europe, was supplied with it. In a single province it is said that nearly a million of persons were at one time employed in this manufacture.

The manufactory at Sevres, in France, has long been celebrated both for the excellence and elegance of its porcelain. There are well-known manufactories of porcelain at Meissen in Saxony, at Berlin, and in Austria; but none of these are at present superior to our own, in Worcestershire and Staffordshire.

Porcelain clay occurs chiefly in countries which abound with granite (251) and gneiss (255). It is found in small quantity in Cornwall, and other granite districts of England, as well as in those of Scotland and Ireland. But the most valuable kinds of this clay are found in China and Japan.

The mineral is not used in the state in which it is found in the earth; but is previously washed several times to free it from impurities. After the process of washing, only about fifteen parts of pure clay remain: this is the kaolin of the Chinese. To form the composition of the porcelain, this clay is mixed, in certain proportions, with quartz (76), flint, gypsum (192), 75steatite (124), or other substances; and the mixture is sifted several times through hair sieves. It is afterwards moistened with rain water, and, in the form of a paste, is put into covered casks. Here a fermentation soon takes place, which changes its smell, colour, and consistence. Its colour passes from white into dark grey; and the matter becomes both tougher and more soft than before. The peculiar mode of preparing this mixture, and the art of rightly managing it, are secrets in most porcelain manufactories.

The next operation consists in giving to the paste thus formed the requisite shape of the vessels. This is done first by kneading it with the hands; and then by taking up certain portions of it, and turning it on a lathe, in the manner of common pottery (115), but with more care.

The third operation is the baking or firing. This is done in furnaces of a particular construction, and generally lasts from thirty-six to forty-eight hours. The state of the baking is shown by proof pieces, as they are called, which are placed in convenient situations, and can be drawn out, from time to time, for examination. The porcelain in this state, is named biscuit porcelain; and figures, and such other porcelain articles as are neither to be painted nor exposed to water are in the state of biscuit.

A fourth operation is covering the surface of the biscuit with a varnish or enamel. This is composed of pure white quartz (76), white porcelain, and calcined crystals of gypsum (192); and sometimes principally of felspar (110). These substances are carefully ground, then diffused through water, and formed into a paste. When used, the paste is diluted in water, so as to give it considerable fluidity; and the pieces of biscuit porcelain are separately plunged into it, in such manner as to cover their whole surface. These are then exposed to a heat sufficient to melt the enamel or covering: and in this state they constitute white porcelain.

If the porcelain is to be painted, it must again be 76exposed to heat in the furnace. The colours used for the painting of it are all derived from metals; and many of them, though dull when applied, acquire considerable lustre by the action of the fire. The colours are always mixed with some kind of flux, such as a mixture of glass (204), borax (208), and nitre, melted together, and afterwards ground.

Gum or oil of lavender is used for mixing up the colours. When the painting is finished, the pieces are exposed to a heat sufficient to melt the flux, and thus fix the colour.

It feels harsh and dry to the touch; is soft, scarcely adheres to the tongue, and will not take a polish from the nail.

This substance obtained its name from having formerly been imported into Europe from Tripoli, on the north coast of Africa. It is, however, now found in several parts of Germany; and a granulated kind has been discovered in England.

Tripoli is used for the polishing of metals and stones. For this purpose, it is mixed with sulphur, in the proportion of two parts of tripoli to one of sulphur. These are well rubbed together on a marble slab, and are applied to the stone or metal with a piece of leather.

When tripoli is combined with red ironstone, it is used for the polishing of optical glasses. It is sometimes made into moulds, in which small metallic or glass figures and, medallions are cast; and a kind of tripoli is found near Burgos, in Spain, which is used as an ingredient in the manufacture of porcelain.

In Derbyshire,, and several parts of Staffordshire, is dug a kind of tripoli which has the name of rotten stone. This is considered to be a produce of limestone shale, which has undergone a decomposition by exposure to the air and moisture. It is used for most of the same purposes as tripoli.

77 CLAY SLATE FAMILY.

It breaks into splinters, does not adhere to the tongue, yields generally a clear sound when struck, and is nearly thrice as heavy as water.

Vast and extensive beds of slate occur in different parts of the world; and this mineral sometimes constitutes even a principal portion of mountains. In our own country there are many important quarries of it, particularly in Westmoreland, Yorkshire, Wales, and Derbyshire.

The uses of slate are numerous and important; but its principal use is for the roofing of houses. For this purpose it is split into thin plates or laminæ. These are fastened to the rafters by pegs driven through them; and are made to lap over each other at the edges, in such manner as to exclude the rain and other moisture. The kinds which are preferred for this purpose are such as have the smoothest surface, and split into the thinnest plates. It is requisite that slates should be damp when they are split, otherwise this cannot be done without difficulty. Hence it is generally customary to split the masses as soon as possible after they have been separated from the rock.

Slate should not be porous. If it be so, rain and snow water will pass through it, and destroy the wood-work of the house on which it is placed. Porous slate is also liable to have moss and lichens grow upon and cover it. These plants retain moisture long, and keep the surface, and even the interior of the slate, moist; so that, during the winter season, by the freezing of the moisture, the slate is apt to split and fall into pieces. To ascertain whether the slate be of requisite compactness, it should be completely dried, then weighed, and afterwards soaked for some time in water. When taken 78out it is to be wiped with a cloth, and again weighed. If it have not acquired any considerable increase of weight, it is a proof of its being sufficiently compact. If, on the contrary, it have absorbed much of the water, and have become considerably heavier by the immersion, it is shown to be of a porous texture. Slates that are brittle are bad. If they emit a tolerably clear sound, when struck with a hammer, it is considered a proof that they are not too brittle: if, on the contrary, the sound be dull, they are soft and shattery. A good slate ought also to resist the action of a considerable degree of heat.

The slates that are principally used in London are brought from North Wales, from quarries that are worked near Bangor. There are also extensive slate quarries near Kendal, in Westmoreland; and the Kendal slates, which are of a bluish green colour, are more highly esteemed than those from Wales. They are not of large size, but they possess great durability, and give a peculiarly neat appearance to the roofs on which they are placed. The slate quarries near Easdale, in Scotland, are so extensive as to furnish annually more than 5,000,000 in number, and to give employment to upwards of 300 men.

French slates were much used in London about seventy years ago; but they have been found too small, thin, and light, to resist the winds and storms of this changeable climate.

Dark-coloured, compact, and solid slates are manufactured into writing slates, or table slates, as they are sometimes called. In the preparation of these, the slate, after it is split of proper thickness, is smoothed with an iron instrument. It is then ground with sandstone, and slightly polished with tripoli (119), and, lastly, rubbed with charcoal powder. It is cut into the requisite shape, set in a wooden frame, and is then ready for use.

For writing on these slates, pencils are used which are also made of slate. These, which are called slate pencils, 79are made of a particular kind of slate, that, on splitting, falls into long splintery fragments. It is necessary that the pencils should be considerably softer than the slate to be written upon, so that they may leave a whitish streak on its surface, without scratching it. Such is the shivery nature of the slate of which they are made, that, if it be exposed for some time to the action of the sun or frost, it is rendered useless. Hence, workmen are careful to cover it up and sprinkle it with water, as soon as it is taken from the quarry, and to preserve it in damp cellars. The pieces are afterwards split by a particular instrument, and then wrought into the requisite shape.

In some of the quarries in Derbyshire and Wales the slate is so thick as to admit of being split into large and tabular pieces. These are used for gravestones, and for slabs for dairies and cellars. Paving stones and mile-stones are also formed of them; and vessels for the salting of meat, and setting of milk in dairies. For the latter use slate is peculiarly well adapted, on account of its resistance of greasy or oily substances. But this property renders it unfit for any purpose for which it is requisite to be painted; as, the oil not entering the stone, the paint soon peels off, and leaves the stone as black as it was at first. Cut into narrow strips, slate has also been applied, in the neighbourhood of Bangor, North Wales, for the formation of fences.

When sufficiently solid for the purpose, slate is cut into inkstands, and turned into vases, and fancy articles of various kinds. And a singular circumstance has been remarked, that, if a window or door be suddenly opened, in an apartment where the workmen are turning these, they will sometimes fly in pieces; though, after the work is finished, they may be exposed to the usual changes of temperature without injury.

Pounded slate is advantageously used for cleaning iron and other works in metal. When well ground, and mixed with a certain proportion of loam, slate is made into moulds for the casting of metals in; and, when 80burned and coarsely ground, is used instead of sand in the making of a solid and impermeable mortar or cement, for the parts of buildings that are covered with water.

It is soft and smooth to the touch, and, in handling, stains the fingers.

To crayon painters, and other artists, black chalk is a very useful article. Considerable quantities of it are imported from France, Spain, and Italy. The best is brought from Italy. This is more free from gritty particles, more firm and compact in its texture, and in its touch much smoother than the chalk of any other country. It contains somewhat more than one-tenth part of its weight of charcoal. When prepared for use, it is cut into square pieces, which are sometimes enclosed in wooden cases, like black lead pencils. These pencils are said to become dry, hard, and unfit for use, by long keeping. To preserve them in greatest perfection, they should be kept in a moist place. Some artists prefer pencils that are made of the chalk finely ground, mixed with a certain proportion of gum water, and cast in moulds. Care should be taken not to put too much gum, as the pencils will not, in such case, leave any mark on the paper.

Drawing slate is sometimes used as a black colour for painting. For this purpose it is pounded or ground, and then mixed with oil or size, according to the kind of work for which it is required. When black chalk is strongly heated, it loses its colour, and assumes that of a reddish grey.

81These stones, when properly cut and smoothed, are of indispensable utility to carpenters, cutlers, and others, for sharpening their cutting instruments upon. Those of the finest grain are used for lancets, penknives, and razors. For this purpose their surface, when used, is covered with a small quantity of oil; by which, after a while, they are rendered considerably harder than they were at first. They ought to be kept in damp and cool places; for, if much exposed to the sun, they become too hard and dry for many purposes to which they are applied.

There is a vulgar and erroneous notion that hones are holly wood, which by lying in petrifying water, have been thereby converted into stone. The greater number of them have a fine and a coarse side. From the circumstance of their having been originally brought into this country from Turkey and the Levant, they are sometimes called Turkey stones. They are now found in Saxony and Bohemia, in North Wales, and near Drogheda, in Ireland.

The powder of whet slate is sometimes used, instead of emery, for the cutting and polishing of metals.

MICA FAMILY.

The colour of mica is greenish, sometimes nearly black, reddish, brown, yellow, or silvery white, with, occasionally, a metallic lustre on the surface. Mica is so soft as easily to be scratched; and, when divided across the plates, seems rather to tear than break.

This is one of the most abundant mineral substances that is known. It not only occurs in a massive and crystallized state, but it enters into the composition of many rocks; is found filling up their fissures, or crystallized 82in the cavities of the veins which traverse them. In some countries, as in Siberia, it is an article of commerce, and is obtained from mines like other minerals. From these it is extracted by hammers and chisels. It is then washed, to free it from the impurities which adhere to it; split into thin leaves or pieces; and assorted into different kinds, according to their goodness, purity, and size. We are informed by the Abbé Haüy, that plates of mica a yard or more in width have been obtained from the mines in some parts of Russia.

Thin plates of mica are adopted, in many parts of Siberia and Muscovy, to supply the place of glass for windows. In the shipping of Russia it is considered preferable to glass, as the concussion produced by the firing of the guns does not shatter it. It is employed instead of window glass in Peru and New Spain; and also in Pennsylvania. Mica may be advantageously substituted for horn in lanterns, as it is not only more transparent, but is not susceptible of injury from the flame of the candle. It has, however, the inconvenience of soon becoming dirty; and of having its transparency destroyed by long exposure to the air. Mica is used for enclosing objects that are intended to be viewed by microscopes.

So plentiful is this substance in Bengal, that, for the value of five shillings, as much of it may be purchased as will yield a dozen panes, each measuring about twelve inches in length and nine in breadth, and so clear as to allow of ordinary objects being seen through them at the distance of twenty or thirty yards.

Mica, when powdered, is sold by stationers on the Continent, in place of sand, for absorbing ink in writing, but it does not dry sufficiently quick to be of much use in this respect. In Russia it is employed in different kinds of inlaid work. It is sometimes powdered, and intermixed with the glaze in particular kinds of earthen ware. The heat which melts the glaze has no effect on 83the mica: hence it appears, dispersed throughout the glaze, like plates or scales of silver or gold. Some artists use it in making artificial avanturines (85).

It must be observed that the best mica is of a pure pearl colour; and, when split into leaves, presents a smooth surface.

SOAPSTONE FAMILY.

It is somewhat more than twice as heavy as water; and is distinguished from indurated talc (135) by not splitting, like that substance, into slaty fragments.

In the counties of Devon and Cornwall, and the islands in the vicinity of the Lizard Point, this mineral is found in considerable abundance. It possesses many of the same properties as fullers’ earth, and is, like that substance, employed in the scouring of woollen cloths. When mixed with water it may be formed into a paste; and, in this state, it is easily worked, like clay, for the manufacture of earthen ware. In the porcelain manufactory at Worcester considerable quantities of steatite are employed. According to Dr. Shaw, the Arabs use it in their baths, instead of soap, to soften the skin.

As it becomes hard in the fire, and does not alter its shape, this substance has been successfully adopted for imitations of engraved gems. The subjects are engraved upon it with great ease in its natural state; it is then exposed to a strong heat; afterwards polished, and then coloured by means of certain metallic solutions.

We are informed by travellers, that some of the savage tribes eat steatite, either alone, or mixed with their food, to deceive hunger. The inhabitants of New Caledonia eat considerable quantities of it. Humboldt, the South American traveller, assures us that the Otomacks, a savage race of people, who live on the banks 84of the Orinoco, are almost wholly supported, during three months of the year, by eating species of steatite, or potter’s clay, which they first slightly bake, and then moisten with water. M. Golberry says that the negroes near the mouth of the Senegal mix their rice with a white kind of steatite, and eat it without inconvenience.

In some parts of Spain a variety of steatite is found, which is used by artists under the name of Spanish chalk. When slightly burned, this mineral is sometimes used as the basis of rouge.

125. Figure Stone is a kind of steatite, which has, internally, a glimmering and resinous lustre, and a slaty or splintery fracture.

From its softness, and yet solidity of texture, this mineral can easily be fashioned into various shapes, even with a knife. Hence in China, where it frequently occurs, it is cut into grotesque figures of various kinds, which the French call magots de la Chine, into cups, vases, pagodas, snuff-boxes, and other articles.

126. MEERSCHAUM, or SEA-FROTH, is a singular kind of mineral, of yellowish or greyish white colour, sometimes so light as to float in water: when fresh dug it has nearly the consistence of wax.

If exposed to a strong heat, it becomes so hard as to yield sparks with steel.

The principal use to which meerschaum is applied is in the formation of the bowls or heads of tobacco-pipes used by the Turks, and the quantity consumed for this purpose is very great. It is found in a fissure of grey, calcareous earth, about six feet wide, near Konie, in Natolia, where upwards of six hundred men are employed in the digging and preparation of it; and the sale of it supports a monastery of dervises established at that place. The workmen assert that it grows again in the fissure, and puffs itself up like froth. It is prepared for use by being first agitated with water in great 85reservoirs, then allowed to remain at rest for some time. The mixture soon passes into a kind of fermentation, and a disagreeable odour, resembling that of rotten eggs, is exhaled. As soon as this smell ceases, the mass is further diluted with water, which, after a while, is poured off. Fresh water is repeatedly added, until the mass is sufficiently washed and purified. The meerschaum, in this state, is dried to a certain degree. It is then pressed into a brass mould, and, some days afterwards, is hollowed out so as to form the head of the pipe. It is subsequently dried in the shade, and lastly is baked. In this state the pipe heads are brought to Constantinople, where they are subjected to further processes. They are first bailed in milk, and next in linseed oil and wax; and, when perfectly cool, are polished with rushes and leather. The boiling in oil and wax renders them capable of receiving a higher polish than could otherwise be given. When thus impregnated, they also acquire, by use, various shades of red and brown, which are thought to add considerably to their beauty. In Turkey, and even in Germany, meerschaum pipes that have been much used are more valued than those newly made, and this solely on account of the colouring they possess. Indeed there are people in those countries whose only employment consists in smoking tobacco pipes, until they acquire the favourite tints of colour. By long use, the heads become black: but if boiled in milk and soap, they are soon rendered white again.

It is asserted that the Turks spread meerschaum on bread, and eat it as a medicine; and that they cover with it the heads and eyes of dead bodies, previously to interment. As it lathers with water like soap, it is used by the Turkish women for washing their hair; and, as it absorbs oily matters, it is occasionally used, as fuller’s earth is with us, for the cleansing and scouring of cloth.

We are informed by Pliny, that a kind of bricks were made by the ancients, so light that, when dried, they 86would float in water. He describes them to have been formed of a spongy kind of earth, and to have had some resemblance to pumice stone, which he says might perhaps be applied to the same purposes as these bricks, if it could be obtained and wrought in sufficient quantity. Bricks of similar description have lately been made of a mineral substance found near Sienna, in Italy, and which is supposed to be meerschaum.

A kind of meerschaum has lately been discovered, in veins, in the serpentine (132) of Cornwall.

It exhibits internally a glimmering lustre; and, when put into water, immediately absorbs it, and breaks down into small pieces with a crackling noise. This mineral is farther distinguished by its fracture being conchoidal, or appearing somewhat like the impression of a shell; and by its adhering strongly to the tongue.

Although bole is at present little used except as a basis of tooth powder, and a coarse kind of paint, it was formerly considered an important article in medicine, and used as an astringent. We are informed that tobacco pipes are sometimes made of this mineral; and that it is employed as an ingredient in the glaze of some kinds of earthen ware.

It is chiefly imported from the Levant; though it has also been found in considerable beds in Silesia and Saxony.

128. LEMNIAN EARTH is a kind of bole of yellowish grey, or yellowish white colour, sometimes marbled with rust-like spots.

It is distinguished from bole by being dry and not unctuous to the touch, dull internally, adhering slightly to the tongue, and its fracture being earthy.

With the ancients this mineral was considered an almost invaluable medicine. They procured it chiefly 87from Armenia, and the island of Lemnos, in the Grecian Archipelago. The Lemnian bole was held so sacred that it was dug in the presence of the priests of Venus, and, after having been mixed by them with goat’s blood, was moulded into cakes, which were impressed with the figure of a goat, to authenticate them. This done, it was administered as a consecrated remedy; and, even so lately as the sixteenth century, the vein of bole in Lemnos was annually opened on the sixth of August, and, after certain prayers by the priests, so much of the earth was taken out as was thought sufficient for the consumption of the ensuing year. The entrance was then closed, and the severest punishments were denounced against any one who should open it without permission. A portion of the earth was sent to Constantinople, where it was made into small cakes, and sealed by the ministers of the Emperor; the remainder was prepared in the island, and was impressed with the seal of the Governor. Not many years ago, it was customary with certain empirics on the Continent, to sell this substance in sealed packets, as a nostrum of great value, and particularly as possessing astringent properties of very extraordinary nature.

129. FULLER’s EARTH is a well-known mineral, generally of greenish colour, more or less mixed with brown, grey, or yellow: of soft and almost friable texture, and somewhat unctuous to the touch.

When put into water it immediately absorbs it, and breaks down into a fine pulp.

This earth is valuable for its property of taking grease out of woollen and other cloths, which, on a large scale, is effected by the operation called fulling, whence its name has been derived. This operation, which is performed by a kind of water mill, called a fulling mill, is particularly necessary with respect to new cloths, to extract from them the grease and oil that have been used in their preparation.

Fuller’s earth was formerly considered an article of 88such importance in England that its exportation was prohibited under severe penalties. It was then employed for most of those purposes for which soap has since been so extensively applied. In the dressing of cloth it is now so indispensable, that foreigners, although they can procure the wool, are never able, without fuller’s earth, to reach the perfection of the English cloths: and, in this country, incalculable quantities of it are consumed. As an article of domestic utility, it might be much more frequently used than it is, as a substitute for soap, in the cleaning and scouring of wooden floors and wainscots.

There are extensive beds of fuller’s earth in several of the counties of England. London is principally supplied from those of Kent, Sussex, and Surrey. At Wavedon, near Woburn, in Bedfordshire, a peculiarly fine kind is dug up from pits at the depth of ten or twelve feet below the surface of the ground; and no country in the world is known to produce fuller’s earth of quality so excellent as that obtained in England.

TALC FAMILY.

130. JADE, or NEPHRITE, is a very hard and tough species of stone, of greenish or olive colour, somewhat unctuous to the touch, and looking as if it had imbibed oil.

It is found massive, in blunt-edged or rounded pieces.

Nothing has so much tended to make this stone known, as a superstitious notion that a piece of it suspended to the neck will dissolve stones in the kidneys. Hence has been attained its appellation of nephrite, or divine stone; and hence have originated all those numerous amulets in the form of oval plates, hearts, fishes, birds, &c. pierced with holes for ribbons to pass through, which are seen in collections of the curious. Some of the Indian nations make talismans of jade.

From the roughness and tenacity of this stone, in addition to its hardness, it is very difficult to be cut and polished; and even the best polish which it is 89capable of taking as so imperfect, that a person ignorant of its nature might consider it to be merely smoothed and rubbed with oil. The ancient artists executed in it many beautiful and delicate figures; and it is impossible but to admire the industry and perseverance by which they produced even chains, and other hollow kinds of work, in jade.

The Turks cut it into handles for sabres and daggers, and into several kinds of vessels, to which they attach great value.

Jade occurs in granite (251) and gneiss (255) in Switzerland; but the most beautiful specimens of this mineral are brought from Persia, Egypt, and Siberia.

131. Axestone is a kind of jade, but differs from it in having a slaty texture; and in being less transparent and less tough. This stone is found in China, New Zealand, and on the banks of the river of Amazons, in America. And it is said that several of the tribes of American Indians form of it the axes which they use in place of iron. To explain how these people have been enabled to work a substance so rebellious as this is even to the file, and to other instruments of steel (of which they know not the use), it has been presumed that, when the stone is first taken from the earth, it is considerably less hard than when, by drying, its humidity is evaporated: that in this state they work it, and subsequently harden it, in some peculiar manner, by exposure to heat.

It is found in beds, and in a massive state; is translucent at the edges; and, when pounded, the powder feels soapy to the touch.

There are few stones likely to prove more valuable in ornamental architecture, both for beauty and durability, than this. It admits of an excellent polish, which is not easily injured by the effects of air or water. It 90is also too hard to suffer the same inconveniences of being scratched or broken as marble; and its colours are stated to be indestructible. And such is the size of many of the blocks of serpentine, that columns of almost any dimensions may be wrought out of them.

Of the serpentine obtained from the Island of Anglesea, and lately known by the name of Mona marble, a great proportion was sent to London by Messrs. Bullock and Co. who, until the death of Mr. Bullock, had a large warehouse and polishing rooms for it in Oxford-street. The prevailing colours of this stone are red and green. The quarries were worked by them to considerable extent. They manufactured it into chimney pieces, slabs, columns, and other articles; and its great beauty, and its excellence, in many respects, over the generality of marbles, will recommend it strongly to the public notice.

The chief places in which serpentine has hitherto been found are near Bareuth, and Zöblitz, in Saxony; in some districts of Cornwall; about six miles west of the Paris copper mine, in the island of Anglesea; at Portsoy, in Bamffshire, and other parts of Scotland; and at Cloghan Lee, in the county of Donegal, Ireland.

At Zöblitz there are some extensive manufactories, in which serpentine is made into vessels and ornaments of various shapes, that are carried for sale over nearly all parts of Germany. Several hundred persons are there employed in the working of this stone.

The name of serpentine is derived from some of the varieties appearing coloured and spotted like a serpent’s skin. This stone, when found intermixed with primitive limestone, or crystalline white marble, differs in no respect from the celebrated verde antique marble (149).

133. POTSTONE, or LAPIS OLLARIS, is a greenish grey stone, unctuous to the touchy and so soft when first taken from the quarry as to yield to the pressure of the nail, yet not easily broken.

It is found in a massive state.

91In consequence of the softness and tenacity of this stone, it can be turned upon a lathe, and otherwise cut and wrought with great ease. Hence, in Egypt, Lombardy, Norway, and other countries where it is found, it is formed into various kinds of culinary vessels and lamps, which harden in drying, and are capable of withstanding the strongest action of fire. Vessels of this description were known to the ancients; and are particularly mentioned by Pliny, the Roman naturalist, who speaks of some that were highly wrought being very valuable.

Potstone is used in some countries for the lining of stoves, furnaces, and ovens; and it is so durable as to have, in some instances, stood unimpaired for several hundred years.

On the banks of the Lake Como, there were some extensive quarries of potstone, which had been worked from the beginning of the Christian era. These quarries, however, fell in, on the 25th of August, 1618, and destroyed the neighbouring town of Pleurs; which had previously obtained by means of them an annual revenue of about sixty thousand ducats.

134. COMMON, or VENETIAN TALC, is an earthy stone, capable of being divided into plates or leaves, which are soft and unctuous to the touch, somewhat transparent, and usually of greenish silvery white colour.

It leaves a white trace when rubbed upon any object.

Mica and talc have a near resemblance to each other; but the plates of the former, when bent, are elastic, while those of the latter are not.

Venetian talc is very abundant in the Tyrol and the Valteline. In a state of powder it renders the skin soft and shining; a property which appears to have suggested the idea of employing it as the basis of the cosmetic named rouge. This is prepared by rubbing together, in a warm mortar, certain proportions of carmine, or extract of the flowers of carthamus tinctorius, 92with finely powdered talc, and a certain portion of oil of benzoin.

The Romans prepared a beautiful blue or purple colour, by combining pounded talc with the colouring fluid of some particular kinds of testaceous animals, that are found among the submarine rocks of the coasts of the Mediterranean. According to Tavernier, the French traveller, the Persians whiten the walls of their houses and gardens with lime, and then powder them with a silvery white kind of talc; which, he says, gives to them a very beautiful appearance. Talc is now used by the Chinese, and was formerly used by the Europeans, in medicine,

It is found in a massive state; and leaves a white trace when rubbed upon any object.

This is a well known substance, which is in great request by carpenters, tailors, hat-makers, and others, as the lines that are drawn with it are not so easily effaced as those that are made with chalk, and particularly as they remain unaltered even under water. If lines be traced with it on glass, they remain invisible, or at least are scarcely perceptible by the naked eye, till breathed upon. This, it has been conjectured, in part depends on the comparative softness of the substance with which the impression is made; the condensation of the breath taking place more readily on the glass than on the talc that covers it, and the impression of the talc becoming more apparent by the contrast.

Indurated talc, when reduced to powder, is frequently employed for the purpose of removing stains, occasioned by grease, from silk and cloth. This it does effectually, and, in general, without injuring even the most delicate colour. Like potstone, it is sometimes manufactured into culinary vessels.

93This mineral is found in several parts of the continent of Europe; and in Cornwall, Scotland, and the Shetland Islands.

The name of asbestos is derived from the Greek language, and signifies that which is inconsumable. This mineral, and particularly a silky variety of it, in long slender filaments, called amianthus, was well known to the ancients. They made it into an incombustible kind of cloth, in which they burned the bodies of their dead, and, by which means, they were enabled to collect and preserve the ashes without mixture. In the manufacture of this article they were not able to weave the asbestos alone; but, in the loom, were obliged to join with it linen or woollen threads, which were afterwards burned away.

Incombustible cloth was purchased by the Romans at an enormous expense. Sir J. E. Smith, when at Rome, saw a winding sheet of amianthus in the Museum of the Vatican. It was coarsely spun, but as soft and pliant as silk. The person who attended him set fire to one corner of it; and the same part burned repeatedly with great rapidity and brightness, without being at all injured. This interesting relic was discovered, in the year 1702, in a funeral urn, and contained burned bones, together with a quantity of ashes. It was nine Roman palms long, and about seven in width, and had been deposited in the library of the Vatican by order of Pope Clement the Eleventh.

Cloth made of amianthus, when greased, or otherwise contaminated with dirt, may be cleansed by throwing it into a bright fire. In this process the stains are burned out, and the cloth is restored to a dazzling white colour. Pliny, the Roman naturalist, informs us that he had himself seen table-cloths, towels, and napkins 94of amianthus taken from the table of a great feast, thrown into the fire, and burned before the company: and by this operation, he says, they became better cleansed than if they had been washed.

The inhabitants of some parts of Siberia manufacture gloves, caps, and purses of amianthus; and in the Pyrenees it is wrought into girdles, ribbons, and other articles. The finest girdles are made by weaving the most beautiful and silky filaments with silver wire. These are much prized by the women, not only on account of their beauty, but from certain mysterious properties they are supposed to possess.

The shorter fibres of amianthus have sometimes been manufactured into paper, but this is too hard for use. It has, indeed, been proposed to preserve valuable documents from fire, by writing them on paper made of amianthus. Such a plan might deserve consideration, if we possessed fire-proof ink; but until this be obtained, the fire-proof paper will be of little use.

When several of the long fibres of this mineral are placed together, they may be formed into wicks for lamps; and it has been asserted that such wicks are incombustible. Kircher, the German philosopher, had a wick made of amianthus which burned for two years without injury, and was at last destroyed by accident. It is said that the inhabitants of Greenland make use of amianthus for the wicks of their lamps.

This substance, although it will long continue unaltered in considerable heat, yet if the heat be much increased it ceases to withstand it, and is melted into a dense kind of scoria. In the island of Corsica asbestos is advantageously employed in the manufacture of pottery. Being reduced into fine filaments, it is kneaded with clay; and vessels made of this mixture are said to be lighter, less brittle, and more capable of sustaining sudden alterations of heat and cold than common earthenware.

95 CHRYSOLITE FAMILY.

It is generally found in fragments and rounded pieces, and rarely crystallized. In the latter case its regular form is an eight, ten, or twelve-sided prism.

Though scarcely harder than glass, and consequently inferior to most other gems in lustre, these stones are not unfrequently used in jewellery, particularly for necklaces and ornaments for the hair; and, when well matched in colour, and properly polished, their effect is very good. They are, however, too soft for ring stones; for, by wearing, they soon become dull on the surface. But it is said that their lustre may, in some degree, be restored by immersing them in olive oil.

To give the greatest brilliancy to this stone, we are informed by Mr. Mawe, that a copper wheel is used, on which a little sulphuric acid, or spirit of vitriol (24), is dropped; and that, during the process, an highly suffocating odour is given out. But he is of opinion that the most advantageous way of working it would be that in which glass is cut.

Chrysolite is imported from the Levant, and is said to be found in Upper Egypt, and on the shores of the Red Sea.

BASALT FAMILY.

138. BASALT is a greyish black and coarse grained stone, which is usually found either in globular distinct pieces or in groups of large columns, each of which has from three to eight sides, and is divided horizontally into numerous stones, that very exactly lie upon, or fit into each other.

The most remarkable assemblages of basaltic columns that are known are those called the Giants’ Causeway, on the coast of Antrim, in Ireland, and the Cave of Fingal, in the island of Staffa, one of the Hebrides, or Western Islands of Scotland.

96The former, which is believed by the common people to have been an artificial production, the vast labour of giants who formerly inhabited the country, consists of an irregular group of many thousand jointed pillars. Most of these are of considerable height; are in general five-sided, fifteen or sixteen inches in diameter, and each perfectly distinct from top to bottom, though so closely and compactly arranged that it is scarcely possible to introduce any thing betwixt them. This assemblage of columns extends into the sea to a distance unknown, and along a tract of the sea coast of nearly six miles.

The Cave of Fingal is accessible only by sea, and is formed by ranges of massive basaltic columns, fifty feet and upwards in height. The stone of which these columns are formed very much resembles that of the Giants’ Causeway.

In several parts of the world large masses of basalt are discovered, composing entire insulated mountains, of somewhat conical form. They are considered by some writers as volcanic productions, but the proofs of this are by no means satisfactory.

Amongst the uses to which basalt has been applied, two of the most important are as materials of an excellent and durable kind for building and paving. When burned and pulverized, these stones impart to mortar with which they are mixed the property of hardening under water. They easily melt, without any addition, into an opaque and black glass; and from them, under a certain modification, bottles of olive-green colour, and of extreme lightness, but great strength and solidity, have been formed. Some of the kinds have been advantageously employed as millstones. Basalt is occasionally used by artists for touch or teststones, to ascertain the purity of gold and silver; and goldbeaters and bookbinders, on the Continent, usually make their anvils or beating blocks of it.

Basalt, though harder, more brittle, and less pleasing in its colours than marble, was in considerable esteem 97among the sculptors of antiquity, on account of its great durability. Many fine works were consequently executed by them in this stone. Pliny, who has described several, states that the columns of it were sometimes so large as to admit of several figures being wrought out of them. The Emperor Vespasian had an entire statue, accompanied by the figures of sixteen children, cut out of a single column of basalt; this statue he placed in the Temple of Peace, and dedicated it to the Nile. The famous statue of Minerva, at Thebes, is described by travellers to have been formed of basalt. Antiques of basalt are always in a much better state of preservation than those of marble. Even such as are dug out of the earth still retain their original polish; and the finest touches of the chisel upon them are still unimpaired.

ORDER III.—SALINE STONES.

LIME, OR CALCAREOUS FAMILY.

This mineral is found in nearly every country of the globe: but, in a native state, has not hitherto been discovered except in combination with some acid.^[3] The 98process of purifying lime, or depriving it of the acid with which it is combined, is by burning. This is done in a large kind of furnace, called a kiln, where the limestone and fuel are heaped in alternate layers. After it has gone through this process it is called quick-lime, and has the above-mentioned appearance and qualities.

The uses of lime are numerous and important. The principal of these is in the formation of mortar, or cement for buildings. For this purpose it is first slaked, by having water poured upon it: a violent heat is thereby excited, and the lime falls into powder: it is then formed into paste by working it with water and sand. This, when dry, becomes extremely solid, hard, and durable. Various examples might be mentioned of buildings nearly two thousand years old, where the lime is, at this day, as hard as the stones which it cements together. Lime is also used for agricultural purposes: when spread upon land it is supposed to hasten the dissolution and putrefaction of all kinds of animal and vegetable substances, and to impart to it a power of retaining the moisture which is necessary for the vigorous growth of corn or grass. It is employed in the refining of sugar, in the manufacture of soap, in the melting of iron, and by tanners, in a state of solution, for dissolving the gelatinous parts of skins, and removing the hair from them. The manufacturers of glue mix it with that article, for the purpose of adding to its strength, and preventing its becoming flexible by the absorption of moisture. This mineral, if well dried, pounded, and mingled with gunpowder, in the proportion of one pound to two, is of great utility in the rending of stones and rocks: the mixture, it is said, will cause an explosion equal in force to three pounds’ weight of gunpowder. Lime, if swallowed or inhaled, is a virulent poison. Hence persons employed in lime-works are subject to very distressing complaints; and hence, if bread be adulterated with lime, it is extremely injurious. Notwithstanding this pernicious quality, lime is of considerable use in medicine. It is chiefly given in a 99state of solution, and in the proportion of half a pound of quick-lime to twelve pints of boiling distilled water. This preparation is called lime water.

The superb basin of Lampi, one of the principal reservoirs which furnishes the canal of Languedoc with water, was, some years ago, found to leak at the junction of the stones. The engineer who had the direction of the works caused lime to be slacked in the water. This, passing through the apertures betwixt the stones, formed a crust, or very white covering, over its whole surface, of so hard and durable a nature, that it now constitutes one solid and undivided substance, which the water cannot penetrate.

CARBONAT OF LIME.

Vast mountains of limestone occur in several countries of the globe; but no where is lime more abundant than in some parts of England and Wales. It forms, in particular, nearly the whole mountainous districts of Derbyshire and Shropshire, and encloses, in its substance, numerous veins of lead ore, calamine, and other important mineral productions.

Its uses have been already described (139).

It is found abundantly in many of the southern counties of England, and is usually procured from large open places, called chalk-pits, by digging. In some parts of Kent, however, the workmen save themselves, in this respect, much trouble. They undermine the sides of hills to a certain depth, then dig a trench at the top as far distant from the edge as the mining extends at the bottom. This trench they fill with water, which soaks through during the night, and the whole 100mass is thereby loosened, and falls down before morning.

The harder and more compact kinds of chalk are cut into blocks, and used as building stones. When burned and formed into lime, chalk becomes an excellent mortar: nearly all the houses in London are cemented with chalk mortar. It is also used as lime in agriculture. As it readily imbibes water, it is used by starch-makers, chemists, and others, to dry precipitates upon. With isinglass or the white of eggs it forms a valuable lute or cement. By artists it is in request for the construction of moulds to cast metals in; and by carpenters and others, as a material to mark with. Chalk is one of the most useful absorbents that are employed in medicine: it likewise gives name to an officinal mixture, to a powder, and a potion.

When pounded and cleared from gritty particles, it has the name of whiting. In this state it is used for the cleaning and polishing of metallic and glass utensils; for whitening the ceilings of rooms, and numerous other purposes. Spanish white is the same substance cleansed with peculiar care; and the Vienna white, which is used by artists, is perfectly purified chalk.

142. MARBLE is a compact and close-grained kind of limestone; so hard as to admit of being polished. It is this quality which principally distinguishes it from other calcareous substances.

Although nearly all the numerous kinds of marble may be burned, and thus converted into quick-lime, their use in ornamental architecture, &c. is so important as, in general, to prevent their application to the inferior purpose of mortar. Marble has been known from a very early period. The Book of Esther, in the Old Testament, describes the palace of Ahasuerus to have had “pillars of marble,” and the pavement of “red, and blue, and white, and black marble.”

It would be impossible, in an elementary work like the present, to describe, or even to enumerate, all the different kinds of marble which were known to the ancients, 101or are known to the moderns. But it is, perhaps, requisite that an account should be given of some of the most important of them.

144. Greek White Marble.—The Marmo Greco, of Italian artists, is of snow-white colour, in fine granulations; and somewhat harder, and consequently capable of higher polish, than most other white marbles. It is found near the river Coralus, in Phrygia.

It is susceptible of a high polish, and is applicable to every species of sculpture, except when, as is too often the case, dark veins intrude, and spoil the beauty of the work. In the centre of the blocks a beautiful kind of rock crystals, called Carrara diamonds, are sometimes found.

During the late war with France, the exportation of statuary marble from the countries under the dominion of Buonaparte was prohibited; and, at one time, it became so scarce in England as to be sold at the rate of more than seven guineas per cubic foot. The block of marble for the statue of his late Majesty in the great Council Chamber at Guildhall, London, was stated by the public prints to have cost twelve hundred guineas.

147. Luni Marble is a snow-white, compact, and finely granular variety, which was obtained by the ancients from quarries on the coast of Tuscany. It was preferred by the Grecian sculptors, both to the Parian and Pentelic marbles; and it is usually supposed that the Belvidere Apollo, as well as the Antinous of the Capitol, was wrought out of this marble. There is now found at Luni a white marble, variegated with red spots and dots.

148. Green antique Marble, or Verde antique of the Italians, is a mixture of white marble and green serpentine (132). This is believed to have been obtained from some part of Italy, but the quarries are not now known.

150. Brocatello Marble is somewhat like the last; but is also irregularly marked with various shades of red, and, in some parts, with white.

151. Mandelato Marble is of light red colour, with yellowish white spots. It is found at Lugezzana, in the Veronese. Another variety, bearing the same name, occurs at Preosa.

152. Verde di Prato Marble is a green marble, marked with darker green spots, which is found near the town of Prato in Tuscany.

153. Lago Maggiore Marble is a beautiful kind, white, with black spots and dots. It has been employed for decorating the interior of many churches in the Milanese.

154. Bretonico Marble.—This beautiful marble, which is found near the village of Bretonico, in the Veronese, is varied with yellow, grey, and rose colour.

FRENCH MARBLES.—155. Many valuable kinds of marble are obtained from different parts of the French territory.

156. Campan Marble.—Three kinds of marble are known by this name, all of them procured from immense quarries at Campan, near Bagnere, in the Pyrenees. The first, called Green Campan, is of pale sea-green colour, and exhibits, on its surface, lines of much deeper green, forming a kind of net-work. The second, called Isabel Campan, is of delicate rose colour, with undulating green veins. The third variety, the Red Campan, is of deep red colour, with veins of still deeper red. The green variegations in this stone are formed by a 104talcy mineral, intermixed with the lime-stone.—The Campan marble is well adapted for slabs, tables, chimney-pieces, and other ornamental purposes in the interior of buildings; but, if exposed to the weather, the talcose substances perish, and leave hollow spaces which render its surface rough and uneven.

157. Griotte Marble is of a deep brown colour, with blood-red oval spots, formed by shells. Its name has been obtained from its brownish colour, being similar to that of the cherries that are called by the French griotte. This marble has, of late, been much used in the decoration of public monuments, and in splendid furniture, in France. Some of the ornaments of the Triumphal Arch of the Carousel are made of it. The department of Herault is the part of France from which it is obtained. It sometimes contains large white veins, which destroy the harmony of the other tints.

158. Marquese Marble.—This, which is obtained from quarries, near the village of Marquese, between Calais and Boulogne, is marked with different shades and variegations of white and brown. Of this marble Buonaparte commenced a magnificent column on the heights near the sea, at Boulogne, to commemorate his victories; but, since his dethronement, the erection of this structure has been discontinued.

159. Sarencolin Marble is distinguished by exhibiting large zones, and angular spots of yellow or blood-red colour. It is found at Sarencolin, in the High Pyrenees.

160. St. Beaume, or Languedoc Marble, is of light red colour, marked with white and grey zones, formed by madrepores. The eight columns which adorn the Triumphal Arch, in the Carousel at Paris, are of this marble. It is obtained from quarries at St. Beaume, in the department of Aude.

161. Breccia Marble of the Pyrenees.—One kind of this marble contains black, grey, and red, middle-sized spots in a brownish red ground. It admits of 105a good polish. Another kind has an orange-yellow-coloured ground, containing small fragments of snow-white colour. Both these are found in the Pyrenees.

SPANISH MARBLES.—162. Few countries are more productive of marble than Spain; and in few countries are the public monuments and buildings more profusely decorated with marble. The vault of the theatre of Toledo is supported by 350 marble columns; and an ancient mosque at Cordova is ornamented with 1200 columns, most of which are of Spanish marble. The palace and church of the Escurial, and many of the churches in Madrid, are decorated with marbles of the most beautiful description.

163. White Spanish Marble.—Near Cordova; at Filabres, three leagues from Almeria, in Grenada; and in some other parts of Spain, white marble is obtained, which is susceptible of a good polish, and is well adapted to the general purposes of sculpture.

164. Seville Marble is a beautiful red variety, with shining red and white spots and veins. In the vicinity of Tortosa is found a kind of marble which has a violet ground, spotted with bright yellow; and near Grenada a marble of green colour, which somewhat resembles the celebrated verde antique (149).

165. Spanish Breccia.—There are several beautiful varieties of breccia in Spain. At Riela, in Arragon, there is one, composed of angular portions or fragments of black marble, embedded in a reddish yellow base. The breccia marble of Old Castile is of bright red colour, dotted with yellow and black, and encloses fragments of pale yellow, brick-red, deep brown, and blackish grey colour.

GERMAN MARBLES.—166. Germany abounds in marbles, and affords many kinds which are remarkable both for beauty and singularity. Of these the kind best known is

106167. Lumachelli Marble.—This exhibits beautiful iridescent colours, which are sometimes prismatic internally, but more commonly of various shades of red or orange; whence it has also obtained the name of fire marble. Few kinds of marble are more generally admired than this. It has a dark ground, and is marked throughout with the appearance of small whitish shells, which, in certain parts, refract the most beautiful and brilliant colours. This marble is cut into the tops and bottoms of snuff-boxes, and several other ornamental articles. It is found in veins at Bleyberg, in Carinthia.

168. Many beautiful kinds of marble are obtained from the island of Sicily, particularly one called Sicilian jasper, which is red, with stripes like ribbons, white, red, and sometimes green. Switzerland abounds in marbles; Portugal, Sweden, and Norway afford few. In the Russian empire many have been noticed, particularly among the Uralian mountains. The late Empress Catharine caused an immense palace to be built for her favourite Orloff, which is entirely coated, both inside and outside, with marble. She built the church of Isaac with marbles of different kinds, on a vast space, near the statue of Peter the Great, in Petersburgh. We are at present very imperfectly acquainted with the marbles of Asia. Dr. Shaw mentions a red marble obtained from Mount Sinai; and Mr. Morier, in his journey through Persia, speaks of a beautiful translucent kind which he calls marble of Tabriz, and the colours of which are light green, with veins sometimes of red, sometimes of blue. He says it is cut into large slabs, some of which he describes to have measured nine feet in length, and five feet in breadth.—No account has hitherto been published of the marbles of Africa.—In the United States of America many kinds of marble have been discovered, some of which have been wrought, and polished; but very imperfect descriptions have yet been given of them.

169. Few countries produce a greater variety of excellent 107marbles than the British Islands. Although these marbles are seldom noticed much beyond the limits of the districts in which they occur, many of them are admirably adapted for ornamental purposes; particularly for slabs and chimney-pieces. It is much to be regretted that we should send to foreign countries for stones which, in many instances at least, could certainly be as well supplied from our own. The following is an enumeration of a few of the most important kinds.

ENGLISH MARBLES.—170. Petworth Marble, when cut into slabs, is equal, both in beauty and quality, to many of the marbles imported from the Continent. The Earl of Egremont has, at Petworth, several chimney-pieces formed of it. Much of this marble was used in the cathedral church of Canterbury. The pillars, monuments, vaults, pavement, and other parts of that venerable structure, have been formed of it. The archbishop’s chair is an entire piece of Petworth marble. This marble is found in greatest perfection upon an estate of the Earl of Egremont, at Kirdford. It lies at the distance of from ten to twenty feet under the surface of the ground, and in flakes or strata nine or ten inches in thickness. Petworth marble is also an excellent stone for walls; and, for paving, it cannot be excelled. When burned, it also constitutes a valuable manure, superior, as some farmers imagine, even to chalk.

171. Purbeck Marble is obtained from the island of Purbeck, in Dorsetshire. It is of dark colour, and contains numerous small round shells, which, when it is cut and polished, mark it with roundish variegations of brown, dark green, and grey. This marble was formerly more used than it is at present. Several of the small columns, and many of the monuments, in the churches of Dorsetshire, and the adjacent counties, are formed of it. But it is not so durable as many other kinds. Wherever it is long exposed to the weather, the surface cracks, splits off, and becomes defaced.

108172. Babbicombe Marble is one of the most beautiful kinds that is found in any country. It varies in colour, from light brown to deep red; and large slabs of it have been obtained that are elegantly and diversely marked, some in streaks, others in spots, and others in different coloured shades.

This kind is quarried at Babbicombe, in Torbay, Devonshire, and is extensively manufactured into chimney-pieces in the West of England. An attempt was lately made to introduce it in London; but, from its not being the production of a foreign country, this has failed of success.

173. Derbyshire Marble.—There are, in Derbyshire, several kinds of marble, most of which contain an abundance of fossil shells, and other remains of marine animals. At Wetton, near Ashbourne, a beautiful kind is obtained, of greyish black colour, which contains a vast number of whitish and very minute shells. This has the name of bird’s eye marble. Near Monyash a beautiful variety is found, of a cheerful colour, inclining to brown red, and full of large marine figures in all directions; these, when the marble is cut, appear white, and afford a pleasing contrast.

174. Kendal Marble.—Some varieties of black, grey, and brown marble, are wrought near Kendal, in Westmoreland. These somewhat resemble the Derbyshire marbles; and, like them, are manufactured into chimney-pieces, and ornamental slabs for houses. Several of the slabs are found to contain corallines, and the remains of other marine animals, which vary their appearance in a very pleasing manner.

The Mona Marble is a species of serpentine intermixed with white limestone: it has been already described (132).

SCOTTISH MARBLES.—Scotland affords many valuable and beautiful varieties of marble.

175. Tirie Marble.—Few of the British kinds of 109marble have been more admired than that obtained from Tirie, one of the Western Islands of Scotland. It is of a reddish, sometimes a delicate rose-coloured tint, and sometimes white; and is always intermixed with other minerals which add to its beauty. The most common of these is of black colour, and called hornblende; the others are pale green sahlite, blackish brown mica (123), and green chlorite. In some varieties the hornblende is more abundant than the marble.

176. Assynt Marble.—At Assynt, in Sutherland, a white marble has been discovered, which is perfectly solid and pure, and entirely free from blemishes or stains. Blocks or slabs of it may be cut of almost any size that can be required. This marble acquires a smooth surface, but remains of a dead hue; whence, of course, its uses as an ornamental marble are much circumscribed.

177. Isle of Sky Marble.—There is found in the Isle of Sky a marble of pure white colour, which appears capable of yielding large and valuable blocks. Its fracture is granular and splintery, and its texture fine. It is harder, heavier, and more compact than the marble of Carrara (146); and is apparently well fitted for all the purposes of sculpture. But it has the defect of being very unequally hard. While some parts of the stone are nearly as easy to work as that of Carrara, other parts are so hard as to add a charge of near fifty per cent. to the cost of the working.

178. Sutherland Marble.—Some beautiful specimens of marble of dark brown colour, veined with whitish, light red, or light brown, have lately been brought from the county of Sutherland. These appear of close texture, are susceptible of a beautiful polish, and are capable of being wrought into extremely beautiful slabs for chimney-pieces and other ornamental purposes.

179. Glen Tilt Marble is of white or grey colour, 110and veined or spotted with yellow or green; some specimens are nearly white. The granulations are peculiarly large; and, in its aspect and composition, the Glen Tilt has great general resemblance to the Pentelic marble (143). This marble has of late attracted the notice of the Duke of Athol, through the suggestion of Dr. Macculloch; and chimney-pieces of it have since been made. It is obtained from a valley of the same name in the county of Perth.

180. Blairgowrie Marble.—A few miles from Blairgowrie, in Perthshire, there is an excellent granulated broad-bedded marble, of sugar-loaf texture, and as white as the finest statuary marble. It may be easily raised in blocks and in slabs of great size, perfectly free from blemishes. This marble is supposed to be well adapted for ornamental architecture, but its large sparry texture renders it unfit for the sculptor.

181. Glenavon Marble is of white colour, with large granular concretions, somewhat like spangles, and as large as the scales of fishes. This is a valuable kind; but its situation in the forest of Glenavon, on the property of the Duke of Gordon, is remote and difficult of access.

183. Blairmachyldach Marble.—In the bed of a river, at the farm of Blairmachyldach, about three miles south of Fort William, is a singular marble, consisting of a black ground, flowered with white. It is of 111fine close grain, but not very hard. The flowering in it is light, and beautiful, like fine needle-work, or rather resembling the frosty fret-work upon glass windows, in a winter morning.

The cutting and polishing of marble appear to have been performed by the ancients nearly in the same manner as it is with us. In polishing, the first substance employed is a sharp, coarse-grained sand. Afterwards a finer sand is used, then emery (58) in different degrees of fineness. These are followed by a red powder called tripoli (119): and the last polish is given with putty.

184. BLACK MARBLE is a species of limestone, of uniform black colour, and easily distinguishable, by an excessively disagreeable smell, which is emitted on rubbing two pieces of it together, or striking it with a hammer.

Few minerals are susceptible of a more beautiful polish than this. It is consequently much used for chimney-pieces, small columns, vases, and other ornamental work. There are two quarries of black marble near Bakewell, in Derbyshire: and it is manufactured to a considerable extent by Messrs. Brown and Co. at Derby, who have fixed up in their ware-rooms a large slab of it as a looking-glass.

By the ancients it was much prized. Marcus Scaurus is said to have ornamented his palace with columns of black marble, each thirty-eight feet high; and many of the monuments of ancient Persepolis were executed in it. M. D’Avejan, Bishop of Alais, used a kind of black marble for paving the apartments of his palace; but the friction and heat rendered it so fetid that his successors were compelled to substitute another species of stone in its place.—The pavements, however, of many churches, and of the porticos of several galleries, on the Continent, are of black marble.

185. CALCAREOUS ALABASTER is a species of limestone of somewhat whitish or yellowish colour, translucent, and internally splendent or shining.

It is nearly a pure carbonat of lime; and occurs in masses, 112hanging, like immense icicles, from the roofs of lime-stone caverns, and also coating the sides of such caverns.

The formation of this substance is deserving of notice. The water which oozes through the crevices of limestone rocks, becomes strongly impregnated with minute particles of lime. This water, when it has reached the roof or side of a cavern, is generally suspended, for a considerable time, before a drop of sufficient size to fall by its own weight is formed. In the interval which thus elapses, some of the particles of lime are separated from the water, owing to the escape of the carbonic acid (26), and adhere to the roof. In this manner successive particles are separated, and are attached to each other, until what is called a stalactite, having somewhat the appearance of an icicle, is formed. These stalactites are sometimes solid, having a lamellar structure; sometimes of a fibrous texture, radiating from the centre to the circumference, as may be observed when they are broken; and sometimes hollow. If the water collects and drops too rapidly to allow time for the formation of a stalactite, it falls upon the floor, and there forms an irregular lump of alabaster, which has the name of stalagmite. In some caverns, the separation of the calcareous matter takes place both at the roof and on the floor; and, in course of time, the substance upon each increasing, they meet, and form pillars, sometimes of great magnitude.

Caverns of this kind occur in almost every country. Those of Derbyshire are well known; but the most celebrated stalactitic cave in the world is that of Antiparos, in the Grecian Archipelago.

The kind of limestone formed in the above manner is what the ancients generally denominated alabaster. It was employed by them for the same purposes as marble, was cut into tables, columns, vases, and sometimes even into statues. They also used it in the manufacture of vases or boxes for containing unguents. It is supposed to have been a vessel formed of this stone that is mentioned in the Gospel of St. Matthew, 113where it is said there came unto our Saviour “a woman having an alabaster box of precious ointment.” In the National Museum at Paris there is a colossal figure of an Egyptian deity, which is cut in a kind of alabaster brought from the mountains between the Nile and the Red Sea.

186. TUFA, or INCRUSTING CARBONAT OF LIME, is a calcareous substance deposited by such water as is impregnated with lime.

It clothes, with a stony coat, the smaller branches of trees, leaves, moss, plants, and other substances; and thus preserves them from decay, by protecting them from the action of the atmosphere.

Most of the substances termed by the common people petrifactions belong to this kind of lime. They are, however, merely covered with, and by no means converted into stone.

The dropping well at Knaresborough, in Yorkshire, is particularly celebrated for them. An overhanging rock, several yards in depth, has been gradually formed of the calcareous matter which the water holds in solution; and, from this rock, it incessantly drops into the basin below. The persons who have the care of the place constantly keep these petrified articles for sale. Even old wigs and hair brooms are subjected to the powers of the water, to furnish subjects for attraction to the visitors. There are other springs of this description in Oxfordshire and Somersetshire, and particularly at Matlock, in Derbyshire. We are informed that at Dalton, on the south side of Mendip, the workmen not unfrequently discover large pieces of oak enveloped in blocks of stone which are four or five tons in weight.

Blocks of tufa are, in some countries, cut and used for building stones; and this substance, when burned, becomes an excellent lime. Pieces of it are sometimes hollowed, and used as filtering stones.

In the British Museum there is a human skull completely incrusted with stone, which was found in the river Tiber.

114The warm baths of Hungary are often so thickly coated at the sides and bottom with tufa, that, during certain intervals, it actually fills up the tubes and canals through which they are supplied. The fur in teakettles is a somewhat similar deposit from water in boiling.

187. PORTLAND STONE, BATH STONE, KETTON STONE, are different kinds of limestone; and, of a texture so hard and compact as to be used in building.

They have their names from the places where they are respectively found, in Portland Island, near Bath, and at Ketton, in the county of Rutland.

Of Ketton stone several of the colleges in Cambridge are built. Its grain has a singular resemblance to the petrified roe of a fish, whence also it is sometimes called roestone. The bridges, St. Paul’s Cathedral, the Monument, and nearly all the buildings of late date in London, are constructed of Portland stone.

Some of these kinds of stone, when first dug out of the quarry, are so soft that they are readily worked into any form which use or ornament may require. This is owing to the moisture with which they are naturally impregnated; but when they once become hardened, by exposure to the sun and air, they are extremely firm and solid. On the contrary, other kinds of limestone that are used for buildings imbibe and retain the moisture of the atmosphere, in consequence of which they burst or are crumbled by frost.

We are informed that Portland stone was first used in London in the reign of James the First, that monarch, by the advice of his architects, having employed it in the construction of the banquetting house at Whitehall. After the great fire in London, it was brought into general use by Sir Christopher Wren.

188. MARL is a combination of clay, silex (76), and lime: and is denominated calcareous, argillaceous, or siliceous, as the lime, clay, or silex, is most abundant.

The calcareous part of marl is frequently composed 115of shells, whence it frequently has the name of shell marl; and where these are predominant, it affords an excellent manure for sandy, dry, gravelly, or light lands. Marl likewise produces very beneficial effects on mossy and clayey soils; and these effects, where it has been properly applied, have been observable for twelve or fourteen years. Some kinds of marl that contain but a small portion of lime have been successfully used in the manufacture of earthenware.

This mineral is usually found at the depth of from five to nine feet beneath the surface of the ground, and deposited between beds of clay and sand. It is dug out with spades; and, in the digging of it, in Ireland, the workmen not unfrequently meet with the horns of deer and other curious fossils.

The usual mode by which persons, generally unacquainted with minerals, distinguish this from other clayey substances, is, to break a small piece of dry marl into a glass of vinegar. If it be marl it will immediately dissolve with considerable effervescence; and the briskness of the effervescence will be in proportion to the quantity of lime which it contains.

189. FLORENCE MARBLE is a kind of indurated or hardened marl, and is remarkable for presenting, when polished, the appearance of ruined edifices or rocks.

This kind of marble is never used in architecture. Little slabs of it are cut for Mosaic work, and to be framed like pictures; and the latter, when of considerable dimensions, are sometimes purchased at a high price. If held at a distance from the eye, an inexperienced observer might mistake a slab of Florence marble for a drawing in bistre. Here, observes a French writer, we remark a shattered Gothic castle, there the mouldering fragments of a cathedral; in one part ruined walls, and in another shattered bastions and towers. But, when we approach the picture, the illusion vanishes, and those imaginary figures which, at a distance, appeared to be so correctly drawn, become 116changed into irregular spots, lines, and shades, which present nothing distinct to the view.

190. Cottam Marble, which, when cut and polished, also exhibits the appearance of a landscape, is a kind of compact marl. It has its name from being found at Cottam, near Bristol.

191. LIAS, or CALP is a kind of limestone of bluish black, or greyish blue colour, and composed chiefly of lime, silex (76), clay, and oxide of iron (21).

This stone, when burned, forms a cement which has the property of setting very strongly under water. It has also, of late years, been employed in a manner which merits particular notice, for the multiplying of copies of drawings and penmanship. A drawing is made on prepared paper with a peculiar kind of ink. A slab of lias, about an inch thick, is then heated; the drawing is placed upon it, and both are passed through a rolling press. The paper is afterwards wetted, and washed from the stone; but the ink, being of a gummy or glutinous quality, becomes in part absorbed by the stone, and remains. The stone is then ready for the printer. Previously to taking off each impression, the stone is wetted with a sponge; fresh ink (which is said somewhat to resemble printers’ ink, and is put on with a ball similar to that used by letter-press printers) is then applied. This is prevented, by the water, from adhering to any part except to the ink that had been absorbed, by the stone, from the paper on which the drawing was originally made. Paper is then placed on the stone, both are passed through a rolling press as before, and a perfect impression of the drawing is made upon the paper.