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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.
Present in the samples were 14 of the 20 organic compounds called amino acids that are used to make proteins - complex molecules that play indispensable roles in the structure, function and ...
3 has the corundum structure, consisting of a hexagonal close packed array of oxide anions with 2 ⁄ 3 of the octahedral holes occupied by chromium. Similar to corundum, Cr 2 O 3 is a hard, brittle material (Mohs hardness 8 to 8.5). [4] It is antiferromagnetic up to 307 K, the Néel temperature. [5] [6] It is not readily attacked by acids.