1 04 Elements of Mineralogy. 



Earth. Mr. Bergman has extrafted from 

 loo parts of mountain cryftal, about 6 of 

 argill, and i of calcareous Earth. 2 Bergm. 

 112. So alfo has Mr. Abilgaard. Denfk. 

 Shrift. 1781. Yet Mr. Gerhard fays, that 

 fome are ib pure as to contain neither. Gerb. 

 Bey f rage, 78 and 85. He alfo fays that the 

 amorphous cryftals, though colourlefs, 1 being 

 long digefted in acids, afforded when treated 

 trith pure pruffian alkali, fome traces of iron, 

 ibid. 85. 



The pureft and moft tranfparent of thefe 

 cryftals form the falfe diamond* called brif- 

 tal, or kerry ftone, diamant SAlengon, &c. 



The coloured tranfparent cryftals derive 

 their tinge generally from metallic particles 

 in exceeding final* f>: oportion ; they all loofe 

 their colour whence .ted; thefe form the falfe 

 Gems. The moft remarkable are the red^ 

 from Oran, in Barbary\ falfe rubies. 



Yellow. From Bohemia; falfe topazes. 

 Green. Falfe emeralds and prafius. 



gi c v Ffom Bohemia and Saxony. 



It is faid that brown cryftals may be 

 cleared by boiling them in tallow. 7. Roz. 

 360. 



Mr, 



