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Line 1: − + − PHYSICAL CHARACTERISTICS:+ + + + − * Color is highly variable. The color can be white or colorless, blue, red, yellow, green, brown, purple, and pink; there are also instance of color zonation. − * Transparency: Crystals are transparent to translucent. − * Crystal System is trigonal − * Crystal Habits include sapphire's typical six-sided barrel shape that may taper into a pyramid, and ruby's hexagonal prisms and blades. − * Hardness is 9 − * Specific Gravity is approximately 4.0+ (above average for translucent minerals) − * Associated Minerals include calcite, zoisite, feldspars, micas and garnets. − * Other Characteristics: Refractive index is around 1.77; pleochroic (meaning color intensity is variable from different viewing directions); striations on parting surfaces. − * Notable Occurrences include Burma; Sri Lanka; North Carolina and Montana, USA; many African localities; several localities in India, and Middle Eastern and Southeast Asian countries. − * Best Field Indicators are extreme hardness, density and crystal habit.<ref>[http://www.galleries.com/minerals/oxides/corundum/corundum.htm]</ref> − <references/>
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'''Corundum''' is the second hardest natural mineral known to science. The hardest mineral, [[diamond]] is still four 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.
'''Corundum''' is a very hard mineral - [[Moh's hardness scale]] of 9, second only to a [[diamond]]. When comparing absolute hardness, a diamond is four times harder than corundum.<ref>http://www.galleries.com/minerals/hardness.htm</ref> A clear and colorless synthetic corundum is often used for watch crystals to resist scratching as it can only be scratched by another corundum surface or a diamond.
Corundum is an aluminum oxide. In perfect form, corundum is clear though various impurities will change the color of the mineral. When colored red, corundum is called a [[ruby]]. Other clear and translucent forms of corundum are called [[sapphire]]s.
== References ==
<References/>
[[category:Geology]]
[[category:Geology]]
[[Category:Minerals]]
[[Category:Minerals]]
[[Category:gems]]
[[Category:gems]]