Corundum mining

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Corundum is a relatively common mineral that once found wide application as an Extensive British ruby and sapphire mining operations in southeast. Corundum Mining in Morogoro, Tanzania | MINING.com Video When the miners reach the gem rich gravel layer they start to collect it and wash it directly in the mine pit. They created in the deep of the pit a small w. Corundum deposits in placer claims of the American Gem Mining INTRODUCTION. CORUNDUM DEPOSITS OF MONTANA. CORUNDUM DEPOSITS OF MONTANA. CORUNDUM DEPOSITS OF.
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 chromium, sapphire its blue shades to the presence of iron and titanium; most corundum contains nearly 1 percent iron oxide. 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. Corundum is a relatively common mineral that once found wide application as an Extensive British ruby and sapphire mining operations in southeast. Corundum Mining in Morogoro, Tanzania | MINING.com Video When the miners reach the gem rich gravel layer they start to collect it and wash it directly in the mine pit. They created in the deep of the pit a small w. Corundum deposits in placer claims of the American Gem Mining INTRODUCTION. CORUNDUM DEPOSITS OF MONTANA. CORUNDUM DEPOSITS OF MONTANA. CORUNDUM DEPOSITS OF.

Corundum, corundum mining, naturally occurring aluminum oxide mineral (Al2O3) that is, after diamond, the hardest known natural substance. Its finer varieties are the gemstones corundum mining and ruby (qq.v.), and its mixtures with iron oxides and other minerals are called emery (q.v.).

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 chromium, sapphire its blue shades to the presence of iron and titanium; most corundum contains nearly 1 percent iron oxide, corundum mining. The mineral readily weathers to other aluminous minerals—e.g., margarite, zoisite, sillimanite, and kyanite. For detailed physical properties, seeoxide mineral.

Corundum crystallizes in the hexagonal system, forming pyramidal or rounded barrel shapes. It is widespread in nature, corundum mining, being found in igneous, metamorphic, and sedimentary rocks. Large deposits are rare, however. Some of the richest deposits occur in India, Myanmar (Burma), Russia, Zimbabwe, and South Africa. The largest corundum, found in Transvaal, S.Af., is 0.65 m (about 2 feet) long and 40 cm (about 1 foot) in diameter.

In addition to its use as a preciousgem, corundum finds some use as an abrasive, owing to corundum mining extreme hardness of corundum mining material (9 on the Mohs hardness scale). It is used for grinding optical glass and for polishing metals and has also been made corundum mining sandpapers and grinding wheels. Because of its high melting point (2,040° C, corundum mining, or 3,700° F), it has also been used in refractories.

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.v.).

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Corundum Ore | Elder Scrolls | FANDOM powered by Wikia

Corundum deposits in placer claims of the American Gem Mining INTRODUCTION. CORUNDUM DEPOSITS OF MONTANA. CORUNDUM DEPOSITS OF MONTANA. CORUNDUM DEPOSITS OF. Corundum mining products are most popular in Domestic Market, Africa, and Southeast Asia. You can ensure product safety by selecting from certified suppliers, including 243 with Other, 72 with ISO9001, and 8 with ISO14001 certification. 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. Corundum ore is worth as much as a steel ingot, so buying corundum and iron ores to smelt steel ingots is more costly than buying steel ingots directly. Ore veins of all types sometimes do not respawn normally (see mining bugs). Because of corundum's hardness (pure corundum is defined to have 9.0 on the Mohs scale), it can scratch almost every other mineral. It is commonly used as an abrasive on everything from sandpaper to large machines used in .

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 chromium, sapphire its blue shades to the presence of iron and titanium; most corundum contains nearly 1 percent iron oxide. Corundum deposits in placer claims of the American Gem Mining INTRODUCTION. CORUNDUM DEPOSITS OF MONTANA. CORUNDUM DEPOSITS OF MONTANA. CORUNDUM DEPOSITS OF. Because of corundum's hardness (pure corundum is defined to have 9.0 on the Mohs scale), it can scratch almost every other mineral. It is commonly used as an abrasive on everything from sandpaper to large machines used in .


Not to be confused with Carborundum.

Corundum
General
CategoryOxide mineral – Hematite group
Formula
(repeating unit)
Aluminium oxide, Al
2O
3
Strunz classification4.CB.05
Dana classification4.3.1.1
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space groupR3c
Unit cella = 4.75 Å, c = 12.982 Å; Z = 6
Identification
ColorColorless, gray, brown; pink to red, orange, yellow, green, blue, violet; may be color zoned, asteriated mainly grey and brown
Crystal habitSteep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular
TwinningPolysynthetic twinning common
CleavageNone – parting in 3 directions
FractureConchoidal to uneven
TenacityBrittle
Mohs scalehardness9 (defining mineral)[1]
LusterAdamantine to vitreous
StreakWhite
DiaphaneityTransparent, translucent to opaque
Specific gravity3.95–4.10
Optical propertiesUniaxial (–)
Refractive indexnω = 1.767–1.772
nε = 1.759–1.763
PleochroismNone
Melting point2044 °C
FusibilityInfusible
SolubilityInsoluble
Alters toMay alter to mica on surfaces causing a decrease in hardness
Other characteristicsMay fluoresce or phosphoresce under UV light
References[2][3][4][5]
Major varieties
SapphireAny color except red
RubyRed
EmeryBlack granular corundum intimately mixed with magnetite, hematite, or hercynite

Corundum is a crystalline form of aluminium oxide (Al
2O
3) typically containing traces of iron, titanium, vanadium and chromium.[2][3] It is a rock-forming mineral. It is a naturally transparent material, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red and padparadscha if pink-orange. All other colors are called sapphire, e.g., green sapphire for a green specimen.

The name "corundum" is derived from the Tamil word Kurundam, which originates from the Sanskrit word Kuruvinda meaning ruby.[6]

Because of corundum's hardness (pure corundum is defined to have 9.0 on the Mohs scale), it can scratch almost every other mineral. It is commonly used as an abrasive on everything from sandpaper to large machines used in machining metals, plastics, and wood. Some emery is a mix of corundum and other substances, and the mix is less abrasive, with an average Mohs hardness of 8.0.

In addition to its hardness, corundum is unusual for its density of 4.02 g/cm3, which is very high for a transparent mineral composed of the low-atomic mass elements aluminium and oxygen.[7]

Geology and occurrence[edit]

Corundum occurs as a mineral in mica schist, gneiss, and some marbles in metamorphicterranes. It also occurs in low silica igneoussyenite and nepheline syeniteintrusives. Other occurrences are as masses adjacent to ultramafic intrusives, associated with lamprophyredikes and as large crystals in pegmatites.[5] It commonly occurs as a detrital mineral in stream and beach sands because of its hardness and resistance to weathering.[5] The largest documented single crystal of corundum measured about 65×40×40 cm (26×16×16 in), and weighed 152 kg (335 lb).[8] The record has since been surpassed by certain synthetic boules.[9]

Corundum for abrasives is mined in Zimbabwe, Russia, Sri Lanka, and India. Historically it was mined from deposits associated with dunites in North Carolina, US and from a nepheline syenite in Craigmont, Ontario.[5]Emery-grade corundum is found on the Greek island of Naxos and near Peekskill, New York, US. Abrasive corundum is synthetically manufactured from bauxite.[5] Four corundum axes dating back to 2500 BCE from the Liangzhou culture have been discovered in China.[10]

Synthetic corundum[edit]

In 1837, Marc Antoine Gaudin made the first synthetic rubies by fusing alumina at a high temperature with a small amount of chromium as a pigment.[11] In 1847, Ebelmen made white synthetic sapphires by fusing alumina in boric acid. In 1877 Frenic and Freil made crystal corundum from which small stones could be cut. Frimy and Auguste Verneuil manufactured artificial ruby by fusing BaF
2 and Al
2O
3 with a little chromium at temperatures above 2,000 °C (3,632 °F). In 1903, Verneuil announced he could produce synthetic rubies on a commercial scale using this flame fusion process.[12]

The Verneuil process allows the production of flawless single-crystal sapphires, rubies and other corundum gems of much larger size than normally found in nature. 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 have become available on the market causing a significant reduction of price in recent years. Apart from ornamental uses, synthetic corundum is also used to produce mechanical parts (tubes, rods, bearings, and other machined parts), scratch-resistant optics, scratch-resistant watch crystals, instrument windows for satellites and spacecraft (because of its transparency in the ultraviolet to infrared range), and laser components.

Structure and physical properties[edit]

Corundum crystallizes with trigonal symmetry in the space group R3c and has the lattice parameters a = 4.75 Å and c = 12.982 Å at standard conditions. The unit cell contains six formula units.

The toughness of corundum is sensitive to surface roughness[13][14] and crystallographic orientation.[15] It may be 6-7 MPa·m1/2 for synthetic crystals,[15] and ~4 for natural[16]

In the lattice of corundum, the oxygen atoms form a slightly distorted hexagonal close packing, in which two-thirds of the gaps between the octahedra are occupied by aluminum ions.

References[edit]

Wikimedia Commons has media related to Corundum.
  1. ^"Mohs' scale of hardness". Collector's corner. Mineralogical Society of America. Retrieved 10 January 2014. 
  2. ^ abAnthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (1997). "Corundum". Handbook of Mineralogy(PDF). III(Halides, Hydroxides, Oxides). Chantilly, VA, US: Mineralogical Society of America. ISBN 0962209724. 
  3. ^ abCorundum. Mindat.org
  4. ^Corundum. Webmineral
  5. ^ abcdeHurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., Wiley, pp. 300–302 ISBN 0-471-80580-7
  6. ^Harper, Douglas. "corundum". Online Etymology Dictionary. 
  7. ^The Mineral Corundum. galleries.com
  8. ^Rickwood, P. C. (1981). "The largest crystals"(PDF). American Mineralogist. 66: 885–907. 
  9. ^Rubicon Technology Grows 200kg "Super Boule", LED Inside, April 21, 2009
  10. ^"Chinese made first use of diamond". BBC. BBC. May 2005. 
  11. ^Duroc-Danner, J. M. (2011). "Untreated yellowish orange sapphire exhibiting its natural colour"(PDF). Journal of Gemmology. 32: 175–178. doi:10.15506/jog.2011.32.5.174. Archived from the original(PDF) on 2013-05-16. 
  12. ^"Bahadur: a Handbook of Precious Stones". 1943. Retrieved 2007-08-19. 
  13. ^Farzin-Nia, Farrokh; Sterrett, Terry; Sirney, Ron. "Effect of machining on fracture toughness of corundum". Journal of Materials Science. 25 (5): 2527–2531. doi:10.1007/bf00638054. 
  14. ^"Fracture-Strength Anisotropy of Sapphire". Journal of the American Ceramic Society. 59: 59–61. doi:10.1111/j.1151-2916.1976.tb09390.x. 
  15. ^ ab"Fracture of Sapphire". Journal of the American Ceramic Society. 52: 485–491. doi:10.1111/j.1151-2916.1969.tb09199.x. 
  16. ^"Corundum, Aluminum Oxide, Alumina, 99.9%, Al 2 O 3". www.matweb.com. 
Corundum from Brazil, size about 2 cm × 3 cm (0.8 in × 1 in).
Crystal structure of corundum
Molar volume vs. pressure at room temperature.
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