Copper ore is found in many tracts throughout India, plumbago in Madras, and corundum in southern India.
The following precious stones are reported: corundum (rubies and sapphires), beryl, topaz, zircon, garnet, amazon-stone, tourmaline, often in large crystals, and variously coloured quartz, also often found in crystals of great size.
African locality must be mentioned.; considerable finds were reported in 1905 and 1906 from gravels at Somabula near Gwelo in Rhodesia where the diamond is associated with chrysoberyl, corundum (both sapphire and ruby), topaz, garnet, ilmenite, staurolite, rutile, with pebbles of quartz, granite, vIII.
It is the hardest known substance (though tantalum, or an alloy of tantalum now competes with it) and is chosen as io in the mineralogist's scale of hardness; but the difference in hardness between diamond (io) and corundum (9) is really greater than that between corundum (9) and talc (1); there is a difference in the hardness of the different faces; the Borneo stones are also said to be harder than those of Australia, and the Australian harder than the African, but this is by no means certain.
Among the less important metals and minerals which are also mined, is corundum of especial purity.
Haematite crystallizes in the rhombohedral system, and is isomorphous with corundum (Al203).
Chaper found diamond with corundum in a decomposed red pegmatite vein in gneiss.
Although the term sapphire is primarily applied to blue corundum, it is often used in a general sense so as to include all corundum of gem quality, regardless of colour.
The mining of corundum was begun at Corundum Hill in Macon county in 1871, and from 1880 to 1902 the output was considerable, but with the discovery of the Canadian corundum Scale, 1:2,500,000 English Miles 20 30 4 0 So County Seats e County Boundaries Railitlays Canals Swamps deposits the importance of those of North Carolina greatly declined.
The great corundum deposits ofCorundumHill,Macon county,N.C.,have yielded good sapphires, and they are found also at Cowee Creek in the same county.