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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 ]
Lustre (British English) or luster (American English; see spelling differences) is the way light interacts with the surface of a crystal, rock, or mineral. The word traces its origins back to the Latin lux , meaning "light", and generally implies radiance, gloss, or brilliance.
Precious opal displays play-of-color (iridescence); common opal does not. Play-of-color is defined as "a pseudo chromatic optical effect resulting in flashes of colored light from certain minerals, as they are turned in white light." The internal structure of precious opal causes it to diffract light, resulting in play-of-color. Depending on ...
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 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".
Emery is a granular rock used to make an abrasive powder. It largely consists of corundum (aluminium oxide), mixed with other minerals such as the iron-bearing spinels, hercynite, and magnetite, and also rutile . Industrial emery may contain a variety of other minerals and synthetic compounds such as magnesia, mullite, and silica.
Adamantine spar is a silky brown variety of corundum. It has a hardness of 9 on the Mohs scale. [1] See also. Yogo sapphire; References This page was last edited ...
Golden sheen sapphire, (or goldsheen sapphire) is a recently discovered variety of corundum. [2] Goldsheen sapphire has been tested and confirmed in lab reports as "natural sapphire" by GIA, GIT, GRS, AIGS, Tokio gem labs and Lotus. Goldsheen sapphire has a golden shine, almost like gold.