Note 29 — Chapter I

On the subject of serpentine some misapprehension exists. Mineralogists apply the term to a soft stone of a green hue with long curling markings through it, which in their form suggest lacertine creatures and account for the name of the stone. It derives its colour from the presence of a large percentage of manganese in union with silica, and contains twelve or so per cent. of water. A penknife scores it easily. The ‘Verde di Prato,’ a dark stone used in bands on Tuscan buildings, of which there is question in a subsequent section, postea, p. 43, is a species of true serpentine.

On the other hand the word ‘serpentine’ is in common use for a dark green stone of quite a different kind, that occurs very commonly in ancient Roman tesselated pavements, and it is this false serpentine that Vasari has in view. It is very hard indeed, and a penknife does not mark it. Professor Bonney describes it as ‘a somewhat altered porphyritic basalt,’ and it is full of scattered crystals of a paler green composed of plagioclasic felspar. These crystals average about the size of grains of maize and they sometimes cross each other, thus justifying Vasari’s description of them. A specimen is B, on the Frontispiece. This stone was found in Egypt, and it is probably the ‘Augustan’ and ‘Tiberian’ stone mentioned by Pliny, Hist. Nat., XXXVI, 7. See Transactions, R.I.B.A., 1888, p. 9. The chief quarry of it however was in the Peloponnesus to the south of Sparta, and the produce of this is called by Pliny, loc. cit., ‘Lacedaemonium viride.’ It should be noted that ‘Verde Antico,’ a green marble of which the chief quarries are in Thessaly, is distinct from both the true and the false ‘serpentine.’