*54 
EARTHS. SILICEOUS. 46. Petrofdex. 
Chert. Zchmeifstr tainer. I, p. lOI. 
Hornftone, Chert. 1 hcm/tn them, 
1. In texture refemfaling lefl’er fplinters, 
Petrofilex opacus. Wail.fyji. min. i. f. 268. «. 9. 
a. With the colours alternating in ftrata. 
Silex polyzonias. Syst. nat. xii. j./t. 71, n. 16. 
2. In texture refembling larger fplinters. 
Petrofilex opacus. Wall. fyst. mia. l.p. 267, ». 8. 
a. Of a greeniili colour. 
Silcx virefcens. Sytl. nat. xii, 3. p. 70. n, \ z. 
Found in Snaeden and Germany, forming veins and beds 
mountains, and frequently in nodules like kernels in rocks! 
colour ufually blue-grey, fometimes grey, blue, and green 
of various lhades: by breathing on it. it difcovers an earth/ 
fmell, and is fometimes fo hard as to ftrike fire with fteel.' 
it decompofes fooner than flint, and does not take fo high * 
poiifti : in the fire it decrepitates and whitens : fpecific gra- 
vity from 2,699. to 2,708. contains filica 72. alumina li' 
carbonate of lime 6. Kir-waa. 
diaphmitu. Semitranfparent, of a common fotm. 
Silex Petrofilex. Syft. nat. xii. 3./. 70. ». 1 1. 
Petrofilex femipellucidus. Wall./yfi. i.p.zyi. n.iz. 
Found with the laft fpecics t colour grey, white, ochraceous* 
rofy, flelh-colour, brownilh -red, yellowifh or reddifh' 
brown, green, or variegated ; it often receives a fine polifh. 
(tyttaljinui. In rough cryftals which are frequently hollow within. 
Beyer them, annal, 1786. 1. p. 63. 2. p. 190. 
1. In 6-fided perfeft prifms. 
2. In 6-fided prifms, terminated each fide by convex furfaces. 
3. In 6-fided prifms, terminated each fide by a 3-fided pyramid- 
4. In cubes. 
5. In 6-fided tables. 
6. In double 4-fided pyramids. 
7. In double 3-fided pyramids, 
8. In double 3-fided deprefled pyramids. 
9. In fingle 3 -fided minute pointed pyramids. 
Found in Saxony, near Schneeburg, fometimes covered with * 
thin earthy coating. 
