What type of rock is corundum

10.07.2020 By Tagis

what type of rock is corundum

Geology of Corundum and Emerald Gem Deposits

Corundum is a rock-forming mineral that is found in igneous, metamorphic, and sedimentary rocks. It is an aluminum oxide with a chemical composition of Al 2 O 3 and a hexagonal crystal structure. The mineral is widely known for its extreme hardness and for the fact that it is sometimes found as beautiful transparent crystals in many different colors. Corundum is not a type of rock. It is a mineral. Minerals have a crystalline structure and a consistent chemical formula.

Corundumnaturally occurring aluminum oxide mineral Al 2 O 3 that is, after diamond, the hardest known natural substance. Its finer varieties are the gemstones sapphire and ruby qq. Corundum in its pure state is colourless, but the presence of small amounts of impurities can impart a broad range of hues to the mineral. Ruby owes its red colour to chromiumsapphire its blue shades to the presence of iron and titanium; most corundum contains nearly 1 percent iron oxide.

The mineral readily weathers to other aluminous minerals— e. For detailed physical properties, see oxide mineral. Corundum crystallizes in the hexagonal systemforming what is total health care or rounded barrel shapes. It is widespread in nature, being found in igneous, metamorphic, and sedimentary rocks.

Large deposits are rare, however. The largest corundum, found in Transvaal, S. In addition to its use as a precious gemcorundum finds some use as an abrasivewhat is the best type of dog for a family to the extreme hardness of the material 9 on the Mohs hardness scale. It is used for grinding optical glass and for polishing metals and has also been made into sandpapers and grinding wheels. In most industrial applications corundum has been replaced by synthetic materials such as alumina, an aluminum oxide made from bauxite.

Artificial corundum may be produced as a specialty product, as for gem use, by slow accretion and controlled growth on a boule in an oxyhydrogen flame. This procedure is known as the Verneuil process q. Additional Info. More About Contributors Article History. Print Cite verified Cite. While every effort how to read my cbc results been made to follow citation style rules, there may be some discrepancies.

Please refer to the appropriate style manual or other sources if you have any questions. Facebook Twitter. Give Feedback External Websites. Let us know if you have suggestions to improve this article requires login. External Websites. The Editors of Encyclopaedia Britannica Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree See Article History.

Alternative Title: crystalline aluminum oxide. Corundum of the variety sapphire from Ceylon. Get a Britannica Premium subscription and gain access to exclusive content. Subscribe Now. Learn More in these related Britannica articles:. Corundum and hematite share a common hexagonal architecture. In the ilmenite structure, iron and titanium occupy alternate Fe-O and Ti-O layers. Corundum is characterized by a high specific gravity 4.

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Distribution

Corundum is a crystalline form of aluminum oxide (Al2O3) with traces of iron, titanium and chromium. It is a rock-forming mineral. It is one of the naturally transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems such as sapphires and rubies. Corundum, naturally occurring aluminum oxide mineral (Al 2 O 3) that is, after diamond, the hardest known natural substance. Its finer varieties are the gemstones sapphire and ruby (qq.v.), and its mixtures with iron oxides and other minerals are called emery (q.v.). Corundum of the variety sapphire from Ceylon © Wendell E. Wilson. Corundum is found in a wide variety of rock types. It is characteristic of A-rich and silica poor environments, and appears in association with other aluminous and/or silica-poor minerals. Plutonic igneous rocks not containing quartz and poor in Fe and Mg usually contain corundum.

View All Videos View Minerals. The Mineral corundum. Corundum is best known for its gem varieties, Ruby and Sapphire. Ruby and Sapphire are scientifically the same mineral, but just differ in color. Ruby is the red variety, and Sapphire is the variety that encompasses all other colors, although the most popular and valued color of Sapphire is blue. Sapphire is also only used to describe the gem variety; otherwise it is simply called Corundum.

Corundum is a very hard, tough, and stable mineral. For all practical purposes, it is the hardest mineral after Diamond , making it the second hardest mineral. It is also unaffected by acid s and most environments. Translucent brown Corundum and Emery are the most common forms of Corundum. These are fairly common forms, and due to their great hardness and prevalence are the most favorable abrasive s.

The industrial term "emery" describing Corundum abrasives is derived from the variety Emery which is mined specifically for its use as an abrasive. Erosion may cause Emery to crumble and form sand, which are sometimes called "black sands. Synthetic gems are also easily created by adding traces of certain color producing elements to the Corundum solution, and letting the solution solidify into a boule , or synthetic, unprocessed "mineral" with a particular shape.

This process is called the Verneuil process. Natural Ruby and Sapphire gemstone s may have their color artificially enhanced or deepened through heat treatment when used as gems. Some dark blue stones from certain localities may also be made a bright blue desirable color. Padparadschah is a very rare and sought after variety. See the gemstone section on Ruby for complete details. In the gem trade, it refers specifically to the blue gem variety of Corundum, unless a color is mentioned as a prefix to sapphire i.

Green Sapphire. Sapphire with a color other than blue is often called a "fancy" in the gem trade. See the gemstone section on Sapphire for complete details. Star Ruby. Star Sapphire. Ruby with a brownish tint comes from Thailand, in the Chantaburi District. Gem quality Sapphire is well-known at Pailin, Cambodia.

Translucent to opaque Ruby, sometimes with asterism , is very abundant at Mysore Mysuru and Subramanium, in Karnataka, India. Africa has recently become a significant producer of Corundum, especially in Madagascar, where it is found in the Zazafotsy Quarry, Ambahatraso; and in Andranondambo, Amboasary District. A famous African locality in which opaque rubies are found in green Zoisite is is in Longido, Kilimanjaro Region, Tanzania.

Another important Tanzanian Ruby mine is Winza, in Arusha. In the U. Montana is also the claim to a few other localities: the Gallatin Gateway and Salesville, Gallatin Co. Large deposits of Emery were once worked near Peekskill, Westchester Co. Let us know how we can update this page Click for more details. We strive for accurate content and locality information. If you feel any of the content is incorrect, or if you feel we are missing vital locality information, please fill out the form below so we can update the site.

If you are requesting a locality be added, please only include significant locality occurences for the mineral. About Minerals. Link Directory Donations Mobile Site. Chemical Formula.

Aluminum oxide. Many colors, including blue, red, violet, pink, green, yellow, orange, gray, white, colorless, and black. Occasionally also multicolored or striped. Crystal System. Crystal Forms and Aggregates. Crystals occur as hexagon ally shaped prismatic and tabular crystals, and as bipyramidal hexagon s that are wider in the center and taper thinly on the ends. Crystals are usually elongated and striated crosswise, and sometimes occur in thin plate s. Crystals are commonly smooth or rounded on the edges due to alluvial action.

Also as barrel-shaped hexagonal crystals, modified octahedron s, massive , and as rounded, waterworn alluvial pebbles. Crystals are sometimes striated or etched.

Transparent to opaque. Specific Gravity. Vitreous to adamantine. None, but commonly exhibits rhombohedral and basal parting. Other ID Marks.

Complex Tests. Insoluble in acid s. In Group. Oxides ; Simple Oxides. Striking Features. Immense hardness , high specific gravity , distinctive crystal shape. In altered metamorphic rocks such as marble and hornfels , in nepheline syenite pegmatite s, and in placer deposit s. Rock Type. Igneous , Sedimentary , Metamorphic. Popularity Prevalence Demand Emery - Black, massive variety of Corundum , with color caused by mixture of Magnetite , Hematite , and Spinel. Padparadschah - Orange-pink gem variety of Sapphire.

Ruby - Pink to red variety of Corundum. Sapphire - Sapphire refers to all gem varieties of Corundum , excluding the red variety of Corundum which is classified as Ruby. Star Ruby - Ruby displaying asterism in the form of a six-rayed star. Star Sapphire - Sapphire displaying asterism in the form of a six-rayed star.

Ultralite - Incorrect term in the gem trade occasionally used to describe blue Sapphire. Ruby and Sapphire are the most famous gemstones after Diamond. They have retained their high value throughout the centuries and are continuously and vigorously mined throughout the world.

Red rubies and blue Sapphires are the most popular Corundum gemstones, though other Sapphire colors such as orange, yellow, and green are becoming increasingly popular in gemstone use.

Corundum has some electrical uses, and non gem material, such as Emery , is used as an abrasive because of its high hardness. The gemstone applications of the Corundum varieties are discussed in greater detail in their own dedicated gemstones pages. Make sure to also see the gemstone section on Ruby and Sapphire. The area of Mogok, Burma Myanmar is the source of some of the best gem -quality Ruby. Another significant Burmese deposit is Mong Hsu, which is currently a major Ruby producer, though its color isn't as fine as the Mogok material.

Sri Lanka, especially the area of Ratnapura, Bibile, and Rakwana, is an excellent source of gem quality Corundum of all colors. The finest and largest crystallized specimens and aggregate s of gem-quality Sapphire are from Sri Lanka. 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.

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