Note 57 — Chapter X · NORTHWARDS HO! TO STYKKISHÓLM AND GRAFARÓS.
Reading edition
It supplied the Hafnafiordite of Forchhammer, leek-green, light, porous, and friable pumice-tuff, containing the following proportions:
Silica,35·89
Alumina,27·36
Protoxide of iron,14·41
Lime,10·86
Potash,9·00
Sulphuric acid,1·55
99·07
Dr W. Lauder Lindsay remarks, “The sp. gr. is usually 2·729; it appears to be a lime-oligoclase, belonging, therefore, to the Felspathic family of minerals.”