SILICA. 
257 
CLASS VI. 
EARTHY MINERALS. 
Composed chiefly or in part of one or more of the earths proper ; they frequently contain 
some alkali or alkaline earth, acid or metallic oxide. 
ORDER I. SILICA. 
I. Minerals in which the silica is nearly pure. 
1. Quartz, and its varieties. 
II. Minerals in which the silica plays the part of acid. 
2. Tabular Spar. 
3. Nemalite. 
4. Serpentine. 
5. Magnesite. 
6. Chondrodite. 
7. Boltonite. 
8. Talc. 
9. Pyroxene. 
10. Hornblende. 
11. Arfwedsonite. 
12. Hypersthene. 
13. Schiller Spar. 
14. Anthophyllite. 
15. Hydrous Anthophyllite. 
QUARTZ. 
Quartz. Cleaveland. — Quartz, Calcedony, Jasper and Hornstone. PhiUips. — Quarz. Haiiy and Bendant. — 
Rhombohedral Quartz. Jameson. — Rhomboedrischer Quarz. Mohs. 
Fig. 129. 
Fig. 130. 
Description. Colour white, grey, less 
frequently black, blue, green, yellow, red 
and brown. It occurs regularly crystallized ; 
also massive, disseminated in plates, stalac- 
titic, reniform, botryoidal, globular, specu¬ 
lar, vesicular and cellular. Primary form 
an obtuse rhombohedron. Fig. 129. P ' on 
P' 94° 24 / (Haiiy ); 94° 15' (Phillips). 
The common form is a six-sided prism ter¬ 
minated by six-sided pyramids, prism6 of 
p on z 141° 4:0'; r on P 120°. Fracture 
