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Corundum is a crystalline form of aluminium oxide (Al 2 O 3) typically containing traces of iron, titanium, vanadium, and chromium. [ 3 ] [ 4 ] It is a rock -forming mineral . It is a naturally transparent material, but can have different colors depending on the presence of transition metal impurities in its crystalline structure. [ 7 ]
Corundum is the name for a structure prototype in inorganic solids, derived from the namesake polymorph of aluminum oxide (α-Al 2 O 3). [1] Other compounds, especially among the inorganic solids, exist in corundum structure, either in ambient or other conditions.
The archetypal asteria is the star sapphire, generally corundum with near uniform impurities which is bluish-grey and milky or opalescent, which when lit has a star of six rays. In the red instance stellate reflection is rarer; the star- ruby occasionally found with the star-sapphire in Sri Lanka is among the most valued of "fancy stones".
The corundum is blue, or sapphire. Wet slab, 10 cm (3.9 in) wide. Emery, or corundite, is a dark granular rock used to make an abrasive powder. The rock largely consists of corundum (aluminium oxide), mixed with other minerals. Industrial emery may contain a variety of other minerals and synthetic compounds.
Sapphires are a color variety of corundum, a crystalline form of aluminium oxide (Al 2 O 3). [14] Corundum is one of the hardest minerals, rating 9 on the Mohs scale. [15] Corundum gems of most colors are called sapphires, except for red ones, which are called rubies. [16] The term "Yogo sapphire" refers only to sapphires from the Yogo Gulch. [17]
The spinels are any of a class of minerals of general formulation AB 2 X 4 which crystallise in the cubic (isometric) crystal system, with the X anions (typically chalcogens, like oxygen and sulfur) arranged in a cubic close-packed lattice and the cations A and B occupying some or all of the octahedral and tetrahedral sites in the lattice.
The jewels are typically made from the mineral corundum, usually either synthetic sapphire or synthetic ruby. Jewel bearings are used in precision instruments where low friction, long life, and dimensional accuracy are important. Their main use is in mechanical watches.
Corundum group minerals have a 2:3 ratio, and includes minerals such as corundum (Al 2 O 3), and hematite (Fe 2 O 3). Rutile group minerals have a ratio of 1:2; the eponymous species, rutile (TiO 2) is the chief ore of titanium; other examples include cassiterite (SnO 2; ore of tin), and pyrolusite (MnO 2; ore of manganese).