170 EARTHS. SILICEOUS. 56. Chalcedonius. 



Found in Mexico t Ceylon, Snjueden, Bohemia, Saxony, and other 

 parts o^ Europe, in veins of primitive rocks, and Ibmetimes in 

 agate biills and kidneys in porphyry: colour violet-blue in 

 various degrees of intenfity, fometimes greenifli, rarely 

 white: texture conchoidal, fibrous granular, orfplintery: 

 luftr'? various degrees of faniparency to nearly opake : cryf- 

 tals fimple 6-fided pyramids, or with faces of different fizes, 

 the p'anes of which are fmooth : yields to the file, is brittle, 

 and eafiiy frangible : fpecific gravity 2,750. contains filica 

 97.50. alumina 0,25. oxyde of iron with a trace of manga- 

 nefe 0.50. Ro/e* 



Pseudocrys' Opake, in a 6-rided prifm terminating at (5ne or both ends 

 in a 6 -Tided pyramid. 



Nitrum opacum. Syli, nat. xii. 3./ 85. n. 3. 2. 



Quarczum rude. Wall, fy it i. /», 216. «. 8. 



Found in Hungary, Bohemia, Saxony, S-uueden, and Barhary: the 

 cryllals fometimes detached, fometimes united : colour vari- 

 ous degrees of white, black, red, or variegated. 



56. CHALCEDONIUS. ConMing of filica, a 

 fmall quantity of alumina with fonietimes about 

 a tenth of linne, and a flight trace of oxyde of 

 iron: hard, lightifh, Ihining within, breaking into 

 indeterminate fragments with (harp edges, com-- 

 pa6i:, not mouldering in the air, of a more or lefs 

 perfedlly conchoidal texture, never opake, tough, 

 admitting a high polifli, and generally of a com* 

 mon form : not melting before the blowpipe. 



Cachohnius Milk-white, fomewhat diaphanous, becoming opake in 



the fire. 

 Achates opalina. Wall. Cyst. I. p.zjz, ». 13. 

 Kachelony. Cronst. mineral, feci. 57. 3. a. 

 Cacholony. SchmeiJJe*- mineral. i./>. 106. 

 Found in the rivers Buchareft and Mongool, and the Feroe ijlands, 



where it lies between the llrata of femitranfparent Chalcedony. 



It is never found in drops or llaladitital. The Kalmucs 



make their idols and domeftic veil'eis of it. 



genutnus. Grey, of a flat texture and common form, not falling 



fpontaneoufly into fragments. 

 Silex vagus. 5>v/, nat. xii. 3 p. 69 n, 8. 

 Achates. Wall fyfU min. i> p. 275. n. 15. 

 Calcedony. Kirnxjun \. p. 297. Schmeijer min. I, p. 105. 

 Chalcedony, Thorn/on chem, 3. /»- 530. Jameijou, i./>. 174. 



