Corundums

Corundum is a crystalline form of aluminium oxide, with impurities or trace elements such as iron, titanium, or chromium. These impurities are what create the wide range of colors to be found in corundum crystals: grays, browns, yellows, greens, blues, purples, reds and pinks. It is a naturally transparent material, but can have different colors when impurities are present. Transparent specimens are used as gems. Corundum is best known for its gem varieties, Ruby and Sapphire. A corundum crystal that is red is called a ruby. All other colors are called sapphires. Sapphires that are not gem variety are simply referred to as corundums. The name "corundum" is derived from the Tamil word (from India) Kurundam which originates from the Sanskrit word Kuruvinda meaning ruby.

Corundum is a very hard, tough, and stable mineral. It is the second hardest mineral after Diamond. It is unaffected by acids and most environments. Translucent brown and emery are the most common forms of corundum, and due to their hardness and availability are used as abrasives. The term "emery" such as “emery cloth” comes from the corundum variety “Emery” which is mined specifically for its use as an abrasive. Erosion may cause Emery to crumble and form what is called "black sand." The most common varieties of corundum Emery - Black, massive variety of Corundum, with color from Magnetite, Hematite, and Spinel. Padparadschah - Orange-pink gem variety of Sapphire (A very rare and sought after variety) Ruby - Red variety of Corundum Sapphire - Refers to all gem varieties of Corundum, except the red variety Star Ruby - Ruby displaying asterism in the form of a six-rayed star. Star Sapphire – a Sapphire displaying asterism in the form of a six-rayed star.

Corundums are found in Burma (Myanmar), Sri Lanka, (The finest and largest crystallized specimens of gem- quality Sapphire are from Sri Lanka) Thailand, Vietnam , Afghanistan, India, Africa, Madagascar, Tanzania and Canada. In the U.S.A. they are found in Montana, California, North Carolina, New York, and Massachusetts. A well-known Ruby locality is the Cowee Creek District, Macon Co., North Carolina, especially the area of Franklin. Large deposits of Emery were found in New York and Massachusetts. Common Minerals found with Corundum are Calcite, Albite, Muscovite, Spinel, Almandine, Kyanite Corundum can be confused with many minerals, particularly the silicates, but the high hardness and specific gravity of Corundum can easily distinguish it from any mineral. Some corundums are SW Fluorescent.

Ref.

www.minerals.net/mineral/corundum.aspx

en.wikipedia.org/wiki/Corundum,

www.mindat.org/min-1136.html,

www.gemsociety.org/article/distinguishing-rubies-pink-sapphires/