On the Corundum Stone from Afia, 537 



be found in Great Britain, and en the Continent of Europe, as well as in Afia ; and the above 

 flight eflays may {how, that obfervations on corundum, in its different {lates of purity, may 

 lead to accurate-diftinftion between fubftances hitherto imperfeftly known, and will lead to 

 a revifion of the filiceous genus, whereby the argillaceous gems may obtain its due pre-emi- 

 nence in mineralogy. When gems, by art, or by rolling in the beds of rivers, have been de- 

 prived of the angles of their cryftals, they are unavoidably fubje£led to uncertain external 

 charafters, which even great praftice cannot render certain ; and hence the unwillingnefs 

 of European Jewellers to deal in coloured gems. I have fome fpecimens of a fapphire-bluc 

 ftone, India cut, very fmall and pellucid •, they were purchafcd in India as fapphires, and 

 were fuppofed to be fluor by a lapidary in London, but are cyanite. The above could 

 fcarcely have happened, if the ftones had been of fufficient fize and value to require much 

 examination, the weight and degree of hardnefs being exceedingly deficient. The colour» 

 therefore, will not be a fafe guide. The diamond, whether white, blue, red, yellow, or green^ 

 can be diftinguifhed by its cryftal, or by its fpecific gravity and hardnefs, or, when it is 

 poliflied, by its luftre. Other ftones, which compofe the order of gems, might equally depend 

 ' on their cryftallization, fpecific gravity, polifli, and hardnefs, for a diftindl arrangement. 

 The near relation of argil, which Bergman gave to this order, is dally confirmed ; and it 

 will be, perhaps, to Mr. Klaproth, more than to any other exifting chemift, that we fliall owe 

 purcorre£l information on the fubjeft of other gems, as we do on the fubjedl of corundum. 



Many of the varieties of corundum, particularly the coloured and tranfparent forts, witia their 

 regular cryftallizations, are yet dtjtderata. Many cryftallized ftones, from defeft of colour, 

 luftre, &c. are of little value in the market, fuch as jargon, chryfolite, tourmaline ; and an 

 infinity of unnamed ftones of Ceylon, Pegu,Siam, &c. would be valuable to the mineralogift,if 

 obtained adhering to their ftrata, and in cryftals, when external form is not obliterated. I have no 

 doubt, when it is known how much fuch information will tend to illuftrate the hiftory of the 

 earth, and particularly that of gems : the fpirit of enquiry, fo laudably afloat in Britifti India, 

 will be dire£ted to attain it. I have not heard of any metallic veins being found in corundum, 

 unlefs a ftone, which Alonfo Barba, lih. i, c. 13, defcribes, fliould give an inftance. •' The 

 chumpi, fo called from its grey colour, is a ftone of the nature of emery, and contains iron ; it 

 is of a dull luftre, difficult to work, becaufc it refifts fire long. It is found at Potofi, at 

 Chocaya, and other places, with the minerals, negrillos, and roficleres." 



Having mentioned tlie varieties of cryftallized and amorphous corundum, and the mifcella- 

 neous lafts relative to my colleftion of that fubftance, from India and China, it might be fuffi- 

 cient to give an icon of the cryftal, and clofe a paper already prolix ; but having with fatisfaftion 

 obferved, within the laft years, the fcience of mineralogy gaining ground in Great Britain, from 

 the knowledge acquired by feveral gentlemen, who have exammed the mines, and formed per- 

 fonal acquaintances with the moft learned and experienced men on the continent, and alfo from 

 ingenious foreigners, who have communicated their obfervations on Englifti foffils, and con- 

 nefted the n with the moft approved fyftems, it may, perhaps, be accepted as a fufficient apology 

 for what follows j that I confider it as a defideratum to Englifh mineralogifts, to be invited to a 

 preference of permanent charafters, which the ftudy of cryftallization has collected, and which. 



promife& 



