EARTHS. SILICEOUS. SS- Quartzum. 169 



c. Convergent. Born,ind» fofs, \,tah.2.f» 16, 



d. Decumbent. 



c. Seated in the manner of the prickles of an echinus upon a 

 larger cryltal or other foffil. 



f. Imbricate, 



Found in almoft every part of the globe, particularly in alpine 

 fituations, and is almoft exclufively confined to primitive 

 rocks, efpecially granite and mica flate : colour various fhades 

 of white, brown, rci, and yellow, fometimes mixed together: 

 fragments indeterminately angular, with very (harp edges; 

 does not lofe its tranfparency in the fire: caufes double re- 

 fratlion : fpccific gravity from 2,650. to 2,888. contains 

 lilica 93,0. alumina 6,0, lime 1,0. Bergman, 



Pseudogem" Coloured, pellucid, of a conchoidal texture, in a 6-fidccl 

 'w** tranfveri^ly ftriate prifni. 



Nitrum fluor. Syst, not, xii. 3,/. 85. «, 3, 



Cryftallus montana. Wall.fyst. iiiiner, l,p, 220, n, 10. 



1. Blackifli, Baum^ miner, i. /». 232. «. 2. 



2. Clove-brown. Wall.fyst, i,^. 222. w. 10. h. 



3. Red. IValUfyfi, i. />. 221. «. 10. a, 



4. Fulvous. Wall.fyst, i. p, 222. n. 10. e« 



5. Yellow. Wall.fyji. 1.^.222. ». 10. d. 



6. Leek-green. Wall, fyji, 1./.222. n, 10. §• 



7. Grafs-green, WalLfyst. \,p, 222. n, 10. f. 



8. Sky-biue. Baum^ miner, i,^. 236. 



9. Deep blue, Baum. miner, i. ^, 231. 



Found chiefly in veins abounding in rock cryftal, of various de- 

 grees of magnitude and tranfparency : they are often fold for 

 gems, but may eafily be diftinguifhed by the different form 

 of their cry ftals and by their lefTer degree of hardncfs and 

 luftre: they yield to the file, and like the rock cryftal, when 

 two pieces are rubbed hard together, they emit a phofpho- 

 refcent light in the dark, and exhale a peculiar empyreu- 

 matic odour, 



dmethystus, Violet-blue, varying in texture, form and degrees of 

 tranfparency. 

 Nitrum violaceum. Syji, nat. xii, 3. p. 85. n, 3. d. 

 ^ryftallus violacea. WalLfyfl, \, p. 221. n, 10. b. 

 Amethyjl*, Kirnx: an mineral, i. p. 246. Schmeiffer I , f, ^^» 

 Amethyft, Jainefon, !•/». 137. Thomfon chem, 3»/«5*^' 



VOL. VIT. — Y 



