314 
DESCRIPTIVE MINERALOGY. 
ORDER II. ALUMINA. 
I. Minerals in which the alumina is nearly pure , or combined with an acid. 
1. Corundum. 3. Automalite. 
2. Spinelle. 4. Gibbsite. 
5. Aluminite ? 
IL Minerals chiefly composed of silica and alumina , combined with some alkali, alkaline 
earth or metallic oxide. 
6. 
Idocrase. 
20. 
Thomsonite. 
7. 
Garnet. 
21. 
Laumonite. 
8. 
Scapolite. 
22. 
Analcime. 
9. 
Staurolite. 
23. 
Chabazite, 
10. 
Feldspar. 
24. 
Epidote. 
11. 
Labradorite. 
25. 
Tourmaline. 
12. 
Albite. 
26. 
Clintonite. 
13. 
Stellite. 
27. 
Andalusite. 
14. 
Mesotype. 
28. 
Bucholzite. 
15. 
Stilbite. 
29. 
Kyanite. 
16. 
Heulandite. 
30. 
Achmite ? 
17. 
Epistilbite. 
31. 
Pitchstone. 
18. 
Apophyllite. 
32. 
Spodumene. 
19. 
Prehnite. 
33. 
Pyrophyllite. 
34. Mica. 
CORUNDUM. 
Corindon. Haiij and Beudant. — Corundum. Cleaveland and Shepard. — Sapphire. Thomson .— Rhombohe- 
dral Corundum. Jameson. — Rhomboedrischer Korund. Mohs. 
Fig. 252. 
Description. Colour blue, red, grey, white, green, yellow, 
brown and black. Streak white. It occurs regularly crystallized ; 
also massive. The primary form is a rhombohedron. Fig. 252. P 
on P 86° 6 / ; P on P / 93° 54k Fracture conchoidal and uneven. 
Lustre vitreous, sometimes inclining to adamantine. Transparent 
to feebly translucent on the edges. Hardness 9.0. Specific gra¬ 
vity from 3.97 to 4.16. Infusible by the blowpipe ; with borax, it 
fuses slowly but perfectly into a colourless glass. It is not acted 
on by acids. Becomes electric when rubbed. 
