![A gemstone or gem (also called a precious or semi-precious stone) is a piece of attractive mineral, which—when cut and polished—is used to make jewelry or other adornments.[1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties th](http://web.archive.org./web/20110903072414im_/http://cdn9.wn.com/pd/74/df/1f726cdad2c44cfd30548d29949c_grande.jpg "A gemstone or gem (also called a precious or semi-precious stone) is a piece of attractive mineral, which—when cut and polished—is used to make jewelry or other adornments.[1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties th")
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| Name | Corundum |
|---|---|
| Category | Oxide mineral – Hematite group |
| Formula | Aluminium oxide, |
| Strunz | 04.CB.05 |
| Dana | 4.3.1.1 |
| Symmetry | Trigonal (2/m) |
| Unit cell | a = 4.75 Å, c = 12.982 Å; Z=6 |
| Color | Colorless, gray, brown; pink to pigeon-blood-red, orange, yellow, green, blue to cornflower blue, violet; may be color zoned, asteriated mainly grey and brown |
| Habit | Steep bipyramidal, tabular, prismatic, rhombohedral crystals, massive or granular |
| System | Trigonal (Hexagonal Scalenohedral) Symbol (2/m) Space group: Rc |
| Twinning | Polysynthetic twinning common |
| Cleavage | None – parting in 3 directions |
| Fracture | Conchoidal to uneven |
| Mohs | 9 (defining mineral) |
| Luster | Adamantine to vitreous |
| Refractive | nω = 1.767–1.772 nε = 1.759–1.763 |
| Opticalprop | Uniaxial (–) |
| Pleochroism | None |
| Streak | White |
| Diaphaneity | Transparent, translucent to opaque |
| Gravity | 3.95–4.10 |
| Melt | 2044 °C |
| Fusibility | Infusible |
| Solubility | Insoluble |
| Other | May fluoresce or phosphoresce under UV |
| Alteration | May alter to mica on surfaces causing a decrease in hardness |
| References | |
| Var1 | Sapphire|var1text = Any color except red |
| Var2 | Ruby |var2text = Red |
| Var3 | Emery |var3text = Black granular corundum intimately mixed with magnetite, hematite, or hercynite |
Corundum is a crystalline form of aluminium oxide () with traces of iron, titanium and chromium.
Corundum for abrasives is mined in Zimbabwe, Russia, and India. Historically it was mined from deposits associated with dunites in North Carolina, USA and from a nepheline syenite in Craigmont, Ontario.
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 from the UV to IR), and laser components.
Category:Aluminium minerals Category:Oxide minerals Category:Superhard materials Category:Tamil words and phrases Category:Hematite group Category:Abrasives Category:Trigonal minerals
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![A gemstone or gem (also called a precious or semi-precious stone) is a piece of attractive mineral, which—when cut and polished—is used to make jewelry or other adornments.[1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties th](http://web.archive.org./web/20110903072414im_/http://cdn8.wn.com/pd/74/df/1f726cdad2c44cfd30548d29949c_thumb.jpg "A gemstone or gem (also called a precious or semi-precious stone) is a piece of attractive mineral, which—when cut and polished—is used to make jewelry or other adornments.[1] However certain rocks, (such as lapis-lazuli) and organic materials (such as amber or jet) are not minerals, but are still used for jewelry, and are therefore often considered to be gemstones as well. Most gemstones are hard, but some soft minerals are used in jewelry because of their lustre or other physical properties th")
