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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 ]
When A is nonmetallic and B is metallic, the structure becomes the antiphase of corundum, called the anticorundum structure type, [8] with examples including β-Ca 3 N 2 [9] and borates. Ternary and multinary compounds can also exists in the corundum structure. The corundum-like structure with the composition A 2 BB'O 6 is called double ...
Sapphire is one of the two gem-varieties of corundum, the other being ruby (defined as corundum in a shade of red). Although blue is the best-known sapphire color, it occurs in other colors, including gray and black, and also can be colorless. A pinkish orange variety of sapphire is called padparadscha.
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Printable version; In other projects Wikidata item; ... Adamantine spar is a silky brown variety of corundum. It has a hardness of 9 on the Mohs scale. [1] See also
Geuda (ගෙවුඩ, pronounced gay-yoo-dah [needs IPA]) is a form of the mineral corundum, or sapphire, found primarily in Sri Lanka. Around 70%-80% of gems mined in Sri Lanka belong to geuda varieties. Because of its semitransparent and milky appearance due to rutile inclusions, these stones have little value as gemstones in their natural ...
The encyclopedia was published by Vietnam's Encyclopedia Publishing House, a constituent unit of Vietnam Academy of Social Sciences. Arranged by Vietnamese-alphabet order, the encyclopedia covers diverse topics ranging from history to child rearing. Since then, it has been converted to electronic versions (CD and ebook) and a free online version.
Vietnam remains a full member of the International Organisation of the Francophonie (La Francophonie) and education has revived some interest in the language. [392] Russian, and to a lesser extent German, Czech and Polish are known among some northern Vietnamese whose families had ties with the Eastern Bloc during the Cold War. [393]