VOL. LXXXVIII.] PHILOSOPHICAL TRANSACTIONS. 365 



the angles of their crystals, they are unavoidably subjected to uncertain external 

 characters, which even great practice cannot render certain ; and hence the un- 

 willingness of European jewellers to deal in coloured gems. I have some speci- 

 mens of a sapphire- blue stone, India cut, very small and pellucid ; they were pur- 

 chased in India, as sapphires, and were supposed to be fluor by a lapidary in Lon- 

 don, but are cyanite. The above could scarcely have happened, if the stones had 

 been of sufficient size and value to require much examination, the weight and de- 

 gree of hardness being exceedingly deficient. The colour therefore will not be a 

 safe guide. The diamond, whether white, blue, red, yellow, or green, can be dis- 

 tinguished by its crystal, or by its specific gravity and hardness, or, when it is 

 polished, by its lustre. Other stones which compose the order of gems, might 

 equally depend on their crystallization, specific gravity, polish, and hardness, for a 

 distinct arrangement. The near relation of argil, which Bergman gave to this 

 order, is daily confirmed ; and it will perhaps be to Mr. Klaproth, more than to 

 any other existing chemist, that we shall owe our correct information on the sub- 

 ject of other gems, as we do on the subject of corundum. 



Many of the varieties of corundum, particularly the coloured and transparent 

 sorts, with their regular crystallizations, are yet desiderata. Many crystallized 

 stones, from defect of colour, lustre, &c. are of little value in the market, such as, 

 jargon, chrvsolite, tourmaline; and an infinity of unnamed stones of Ceylon, Pegu, 

 Siam, &c. would be valuable to the mineralogist, if obtained adhering to their strata, 

 and in crystals whose external form is not obliterated. I have no doubt, when it is 

 known how much such information will tend to illustrate the history of the earth, 

 and particularly that of gems, that the spirit of inquiry, so laudably afloat in British 

 India, will be directed to attain it. I have not heard of any metallic veins being 

 found in corundum, unless a stone which Alonso Barba, lib. i, c. 13, describes 

 should give an instance. " The chumpi, so called from its grey colour, is a stone 

 of the nature of emery, and contains iron ; it is of a dull lustre, difficult to work, 

 because it resists fire long. It is found at Potosi, at Chocaya, and other places, 

 with the minerals negrillos and rosicleres." 



Having mentioned the varieties of crystallized and amorphous corundum, and 

 the miscellaneous facts relative to my collection of that substance from India and 

 China, it might be sufficient to give an icon of the crystal, and close a paper 

 already prolix ; but, having with satisfaction observed, within the last years, the 

 science of mineralogy gaining ground in Great Britain, from the knowledge ac- 

 quired by several gentlemen who have examined the mines, and formed personal 

 acquaintance with the most experienced and learned men on the continent, and 

 also from ingenious foreigners, who have communicated their observations on 

 English fossils, and connected them with the most approved systems, it may per- 

 haps be accepted as a sufficient apology for what follows, that I consider it as a de- 

 sideratum to English mineralogists, to be invited to a preference of permanent cha- 

 racters, which the study of crystallization has collected, and which promises to be a 



