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Article: Corundum


General Information and Physical Properties of Corundum

  • Corundum is an oxide mineral belonging to the Hematite group.
  • Its chemical formula is represented by the repeating unit.
  • It is classified under the Strunz classification as 4.CB.05 and under the Dana classification as
  • Corundum has a trigonal crystal system with a hexagonal scalenohedral crystal class.
  • It has a space group of R3c and a density of 4.02g/cm.
  • Corundum is a mineral composed of aluminum oxide.
  • It has a hardness of 9 on the Mohs scale, making it one of the hardest minerals.
  • Corundum can occur in a variety of colors, including red (ruby) and blue (sapphire).
  • It has a high refractive index, giving it excellent brilliance and luster.
  • Corundum is chemically inert and resistant to most chemicals.
  • Corundum crystallizes with trigonal symmetry in the space group R3c.
  • Its lattice parameters are a = 4.75 Å and c = 12.982 Å at standard conditions.
  • The unit cell of corundum contains six formula units.
  • The toughness of corundum is influenced by surface roughness and crystallographic orientation.
  • In the corundum lattice, oxygen atoms form a slightly distorted hexagonal close packing, with aluminum ions occupying two-thirds of the octahedral sites.
  • Corundum is the second hardest natural mineral after diamond.

Gem Varieties of Corundum

  • Corundum has two primary gem varieties: ruby and sapphire.
  • Rubies are red due to the presence of chromium, while sapphires exhibit a range of colors depending on the transition metal present.
  • Padparadscha sapphire is a rare pink-orange variety of corundum.
  • The name 'corundum' is derived from the Tamil-Dravidian word 'kurundam' meaning ruby-sapphire.
  • Corundum is a naturally transparent material, but its color varies based on impurities in its crystalline structure.

Uses of Corundum

  • Corundum is commonly used as an abrasive on sandpaper and large tools in metal, plastic, and wood machining.
  • Emery, a variety of corundum, is used as an abrasive and is mixed with magnetite, hematite, or hercynite.
  • Corundum is used in the production of mechanical parts, scratch-resistant optics, watch crystals, and instrument windows for satellites and spacecraft.
  • It is also utilized in the manufacture of laser components and ceramic armor due to its high hardness.
  • The gravitational wave detectors KAGRA and Advanced LIGO use sapphire mirrors made from corundum.
  • Corundum is widely used as an abrasive due to its hardness.
  • It is used in the production of grinding wheels, sandpaper, and polishing compounds.
  • Corundum is also used in the manufacturing of refractory materials, such as bricks and crucibles.
  • It is a key component in the production of synthetic sapphires for various applications.
  • Corundum is used in the electronics industry for making insulating substrates.

Industrial and Technological Applications of Corundum

  • Corundum is used as a component in armor plating due to its high hardness and toughness.
  • It is used in the production of cutting tools, such as drill bits and saw blades.
  • Corundum is used in the manufacturing of high-temperature resistant ceramics.
  • It is used as a catalyst support in various chemical processes.
  • Corundum is used in the production of specialized lenses and windows for optical devices.
  • Corundum is used in the construction of mirrors for gravitational wave detectors.
  • It is used in the production of core optics components for advanced laser interferometers.
  • Corundum is used in the development of high-performance ceramic materials.

Geology, Occurrence, and Interesting Facts about Corundum

  • Corundum occurs in mica schist, gneiss, marbles, and low-silica igneous rocks like syenite and nepheline syenite.
  • It can be found adjacent to ultramafic intrusives, lamprophyre dikes, and as large crystals in pegmatites.
  • Corundum is commonly found in stream and beach sands as a detrital mineral due to its hardness and resistance to weathering.
  • Major corundum deposits are mined in countries like Zimbabwe, Pakistan, Afghanistan, Russia, Sri Lanka, and India.
  • Synthetic corundum is produced using various methods and is available on the market at a lower cost than natural stones.
  • Corundum has been used in jewelry for centuries and is highly valued for its beauty and durability.
  • The largest corundum crystal ever found weighed over 250 kilograms.
  • Corundum is often found in metamorphic rocks, such as marble and schist.
  • Synthetic corundum can be created through various processes, including flame fusion and flux growth.
  • Corundum has been used in the study of crystallography, fracture mechanics, and material strength.

Corundum Data Sources

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