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www.mineralgallery.co.za Minerals A-E |
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Corundum |
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Name
Corundum
Chemistry
Al2O3, Aluminum Oxide
Uses
As an abrasive and as a gemstone
Color
Blue-Saphire, Red-Ruby
Hardness
9
Specific gravity
3.9-4
Crystals
Trigonal barrel shaped prismatic to tabular
Accompanied by:
Hematite, magnitite or spinel
Fracture
Uneven to conchoidal
Luster
Adamantine to vitreous
Cleavage
None basal parting.
Streak
White
Similar to:
Beryl
Corundum is a widespread and common aluminum oxide mineral from which the gemstones ruby and sapphire, and the abrasive material emery, are made.
Common corundum, which includes all dull, opaque varieties, is usually light blue to gray, brown, or black. It occurs in feldspathoid-bearing igneous rocks as an accessory mineral, in recrystallized limestone, in placer sands, and in aluminum-rich metamorphic rocks. The mineral is found worldwide, with the finest rubies from Myanmar (Burma) and sapphires from Southeast Asia and Australia.
The red variety of corundum is known as ruby
All the other colors of corundum are known as sapphire.
Corundum is the second hardest natural mineral known to science. The hardest mineral, diamond is still hundred and forty times harder than corundum. The hardness of corundum can be partially attributed to the strong and short oxygen-aluminum bonds. These bonds pull the oxygen and aluminum atoms close together, making the crystal not only hard but also quite dense for a mineral made up of two relatively light elements.
The color can be white or colorless, blue, red, yellow, green, brown, purple, and pink; there are also instance of color zonation. Crystals are transparent to translucent. Sapphire's forms typical six-sided barrel shape that may taper into a pyramid, and ruby's hexagonal prisms and blades.
