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Encyclopedia > Transparent alumina
Corundum

General
Category Mineral
Chemical formula aluminium oxide, Al2O3
Identification
Color Brown to grey, less often red, blue, white, yellow.
Crystal habit Steep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular
Crystal system Trigonal Hexagonal Scalenohedral bar32/m
Twinning Polysynthetic twinning common
Cleavage None - parting in 3 directions
Fracture Conchoidal to uneven
Mohs Scale hardness 9
Luster Adamantine to vitreous
Refractive index nω=1.768 - 1.772 nε=1.760 - 1.763, Biref 0.009
Pleochroism None
Streak White
Specific gravity 3.95-4.1
Fusibility Infusible
Solubility Insoluble
Major varieties
Sapphire Any color except red
Ruby Red
Emery Granular

Corundum (from Tamil kurundam) is a crystalline form of aluminium oxide and one of the rock-forming minerals. It is naturally clear, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red, while all other colors are called sapphire. In addition to its hardness, corundum is unusual for its high density of 4.02 g/cm³ which is very high for a transparent mineral composed of the low atomic mass elements aluminium and oxygen. Corundum File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Minerals are natural compounds formed through geological processes. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... Aluminium oxide is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In crystallography, the rhombohedral (or trigonal) crystal system is one of the 7 lattice point groups. ... It has been suggested that twin boundary be merged into this article or section. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... For fractures in geologic formations, see Rock fracture. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Lustre (American English: luster) is a description of the way light interacts with the surface of a crystal, rock or mineral. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... Minerals are natural compounds formed through geological processes. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Fusibility is the ease with which a material will melt. ... Solubility refers to the ability for a given substance, the solute, to dissolve in a solvent. ... Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... Ruby is a red gemstone. ... Emery is a very hard rock type used to make abrasive powder. ... Tamil (Thamizh) is a classical language of the Dravidian language family. ... Quartz crystal Copper(II) sulfate and iodine crystal Synthetic bismuth crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid... Aluminium oxide is a chemical compound of aluminium and oxygen with the chemical formula Al2O3. ... The rocky side of a mountain creek near Orosí, Costa Rica. ... Minerals are natural compounds formed through geological processes. ... Transparent glass ball In optics, transparency is the property of allowing light to pass. ... A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. ... Ruby is a red gemstone. ... Red may be any of a number of similar colours at the lowest frequencies of light discernible by the human eye. ... Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... In physics, Density is defined as mass m per unit volume V. Mathematically, it is expressed as where, in SI units: ρ (rho) is the density of the substance, measured in kg m-3 m is the mass of the substance, measured in kg v is the volume of the substance... The atomic mass of a chemical element is the mass of an atom at rest, most often expressed in unified atomic mass units. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ...


Due to corundum's hardness (typically 9.0 Mohs), it is commonly used as an abrasive in machining, from huge machines to sandpaper. Some emery is a mix of corundum and other substances, and the mix is less abrasive, with a lower average Mohs hardness near 8.0. An abrasive is a material that is used to smooth, machine, or, in some cases, roughen another softer material through extensive rubbing. ... sheets of sandpaper Sandpaper is a form of paper where an abrasive material has been fixed to its surface; it is part of the coated abrasives family of abrasive products. ... Emery is a very hard rock type used to make abrasive powder. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ...


Corundum occurs as a mineral in mica schist, gneiss, and some marbles in metamorphic terranes. It also occurs in low silica igneous syenite and nepheline syenite intrusives. Other occurrences are as masses adjacent to ultramafic intrusives, associated with lamprophyre dikes and as large crystals in pegmatites. Because of its hardness and resistance to weathering, it commonly occurs as a detrital mineral in stream and beach sands. Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... Gneiss Gneiss (IPA: ) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks. ... Venus de Milo, front. ... Metamorphic rock is the result of the transformation of a pre-existing rock type, the protolith, in a process called metamorphism, which means change in form, derived from the Greek words meta, change, and morphe, form. The protolith is subjected to extreme heat (>150 degrees Celsius) and pressure causing profound... Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Syenite leucocratic variety of nepheline syenite from Sweden (särnaite). ... Nephelene syenite is a holocrystalline plutonic rock that consists largely of nepheline and alkali feldspar. ... Pluton redirects here. ... Ultramafic (or ultrabasic) rocks are igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). ... Lamprophyres (Greek Lampros, bright, and the terminal part of the word porphyry, meaning rocks containing bright porphyritic crystals) are a group of rocks containing phenocrysts, usually of biotite and hornblende (with bright cleavage surfaces), often also of olivine and augite, but not of feldspar. ... A dike in geology refers to a tabular intrusive igneous body. ... This article or section does not cite its references or sources. ...


Corundum for abrasives is mined in Zimbabwe, Russia, and India. Historically it was mined from deposits associated with dunites in North Carolina and from a nepheline syenite in Craigmont, Ontario. Emery grade corundum is found on the Greek island of Naxos and near Peekskill, New York. Abrasive corundum is synthetically manufactured from bauxite. Dunite is an igneous, plutonic rock, of ultramafic composition, with coarse grained or phaneritic texture. ... Official language(s) English Capital Raleigh Largest city Charlotte Area  Ranked 28th  - Total 53,865 sq mi (139,509 km²)  - Width 150 miles (240 km)  - Length 560[1] miles (901 km)  - % water 9. ... The ghosttown of Craigmont is located at the base of Robillards Hill which rises 600ft. ... Emery may refer to: Emery (mineral), a rock used to make abrasives, largely consisting of the mineral corundum, but often containing other hard minerals such as hercynite (iron spinel) Emery Worldwide, a cargo airline Emery (band), a Christian post-hardcore band Emery board, nail filers Emery as a place name... The primary use of “Naxos” is as the name of a Greek island in the Cyclades. ... Peekskill, New York is a distinct scenic community along the Hudson River, located in an area where the river winds through the Bear Mountain highlands. ... Bauxite with penny Bauxite with core of unweathered rock Bauxite is an aluminium ore which consists largely of the Al minerals gibbsite Al(OH)3, boehmite and diaspore AlOOH, together with the iron oxides goethite and hematite, the clay mineral kaolinite and small amounts of anatase TiO2. ...


Synthetic Corundum

Gem-quality synthetic corundum is usually produced by the flame-fusion method (also called Verneuil process). This allows the production of large quantities of sapphire, rubies, and other corundum gems. It is also possible to grow gem-quality synthetic corundum by flux-growth and hydrothermal synthesis. Because of the simplicity of the methods involved in corundum synthesis, large quantities of these crystals became available on the market causing a significant reduction of price in recent years. Apart from ornamental use, synthetic corundum is also used to produce mechanical parts (tubes, rods, bearings, and other machined parts), watch crystals, and lasers. The Verneuil process, also called flame fusion, is a method of manufacturing synthetic gemstones, developed in 1902 by the French chemist Auguste Verneuil. ... Sapphire (from Hebrew: ספּיר Sapir) is the single-crystal form of aluminium oxide (Al2O3), a mineral known as corundum. ... Ruby is a red gemstone. ... Hydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high vapor pressures; also termed hydrothermal method. The term hydrothermal is of geologic origin. ... For alternative meanings see laser (disambiguation). ...


References


  Results from FactBites:
 
Glossary of Jewelry Related Terms: Amethyst Jewelry A (2283 words)
Albite: A common white feldspar composed of a silicate of alumina and soda.
Alumina is the base of aluminous salts, a constituent of feldspars, micas, etc., and the characterizing ingredient of common clay, in which it exists as an impure silicate with water, resulting from the erosion of other aluminous minerals.
It is transparent to translucent and can range in color from honey-colored to pale reds, blues and greens to clear or white.
Transparent alumina - Wikipedia, the free encyclopedia (280 words)
Transparent alumina is alumina (aluminum oxide, Al) that is transparent.
As a powder or solid formed by sintering (welding together small particles), alumina is opaque or translucent.
This sintered alumina is very hard, nearly transparent, and has a very high melting point (2303 kelvins), yet like other sintered materials it can be produced at temperatures much lower than its melting point.
  More results at FactBites »

 
 

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