314 



DBSCRIPTIVE MINERALOGy. 



ORDER II. ALUMINA. 



I. Minerals in which the alumina is nearly pure, or combined with an acid. 



1. Corundum. 



2. Spinelle. 



3. Automalite. 



4. Gibbsite. 



5. Aluminite ? 



II. Minerals chiefly composed of silica and alumina, combined with some alkali, alkaline 



earth or metallic oxide. 



6. Idocrase. 



7. Garnet. 



8. Scapolite. 



9. Staurolite. 



10. Feldspar. 



11. Labrador! te. 



12. Albite. 



13. Stellite. 



14. Mesotype. 



15. Stilbite. 



16. Heulandite. 



17. Epistilbite. 



18. Apophyllite. 



19. Prehnite. 



34. Mica. 



20. Thomsonite. 



21. Laumonite. 



22. Analcime. 



23. Chabazite. 



24. Epidote. 



25. Tourmaline. 



26. Clintonite. 



27. Andalusite. 



28. Bucholzite. 



29. Kyanite. 



30. Achmite? 



31. Pitchstone. 



32. Spodumene. 



33. I'yrophyllite. 



CORUNDUM. 



Coiindon. Havy nai BeudarU. — Corundum. Ckaveland and Shepard. — Sapphire. Tkomson. — Rhombohe- 

 dial Corundum. Jameson. — Rhomboedri$cher 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° 54'. 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. 



