Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/353

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343
Mr. William Phillips on the Oxyd of Tin.

work, containing it is said the value of ten or eleven guineas in weight of gold. It is in the collection formerly belonging to the late Philip Rashleigh, Esq. of Menabilly.

Tin is not found mineralized by any other metal, and rarely in intimate combination with any other, except with copper in that mineral which is known by the name of sulphuret of tin. This substance has also obtained the names of bell-metal ore and pyritous tin. It is the Zinnkies of the Germans, the Etain pyriteux of the French, and has hitherto only been discovered in a mine called Huel Rock in the parish of St. Agness, in mass, never crystallized.[1] According to Klaproth, it contains tin 34, sulphur 25, copper 36, iron 2. Its colour is steel-grey, passing into bronze-yellow, in some parts inclining to silvery. Its fracture is unequal and granular. According to Klaproth, its specific gravity is 4.350; under the blowpipe it emits a sulphurous odour, and passes into a blackish slag: it gives a yellow tinge to glass of borax. Its lustre is metallic. It is brittle and easily frangible.

Among the specimens of oxyd of tin in my collection, it may be observed occurring

In Granite—in minute crystals interspersed through granite, from the south-west side of St. Michael's Mount—in granite, with chlorite and schorl from the south side of Redruth Church-town—with schorl in granite from near St. Just. In decomposing granite from Polgooth mine.
  1. Kirwan has described this mineral as “Tin mineralized by sulphur and associated with copper.” On this definition Haüy has the following remark. “It may be proved by other examples, that this celebrated chemist is of opinion, which appears to me to be well founded, that a principle that presides in regard to quantity, may be only an accessory. Mineralogy will have made a great stride towards perfection, when this distinction between essential principles and those which are only accidental, shall be correctly applied to all minerals to which it strictly appertains.”