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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.
Corundum from Brazil, size about 2×3 cm. The most common form of crystalline aluminium oxide is known as corundum, which is the thermodynamically stable form. [16] The oxygen ions form a nearly hexagonal close-packed structure with the aluminium ions filling two-thirds
Crystal structure of sapphire Sapphire ring made c. 1940. Rubies are corundum with a dominant red body color. This is generally caused by traces of chromium (Cr 3+) substituting for the (Al 3+) ion in the corundum structure. The color can be modified by both iron and trapped hole color centers. [25]
The corundum (α-Al 2 O 3) has a rhombohedral structure (space group ¯ nr. 167, Strukturbericht notation D5 1), which cell parameters are: a = 5.128 Å ; α = 55.47 °. The motto is made of two hexaheral groups which height is 2.73 Å. The symetry planes of the groups are 7.21 Å away.
The basic structure of corundum is identical to gibbsite except the hydroxides are replaced by oxygen. Since oxygen has a charge of −2 the layers are not neutral and require that they must be bonded to other aluminiums above and below the initial layer producing the framework structure that is the structure of corundum.
The name "corundum" is derived from the Tamil-Dravidian word kurundam (ruby-sapphire) (appearing in Sanskrit as kuruvinda). Because of corundum's hardness (pure corundum is defined to have 9.0 on the Mohs scale), it can scratch almost all other minerals.
There are two ways to do this, which can be thought of as two notations which represent the same structure. In the usual so-called obverse setting, the additional lattice points are at coordinates ( 2 ⁄ 3 , 1 ⁄ 3 , 1 ⁄ 3 ) and ( 1 ⁄ 3 , 2 ⁄ 3 , 2 ⁄ 3 ), whereas in the alternative reverse setting they are at the coordinates ( 1 ⁄ 3 ...