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Corundum

IMA-Approved Mineral Species


Properties and Data
Physical Properties
Composition
Al2O3
Chemical Name
Aluminium Oxide
Molecular Weight
101.96 g/mol
Density
3.95 - 4.1 g/cm3
Mohs Hardness
9
Melting Point
2044 °C (3711 °F)
Member of
Hematite Group
Crystal System
Trigonal
Optical Properties
Type
Uniaxial (-)
Refractive Index
nω = 1.762 - 1.788
nε = 1.759 - 1.763
Dispersion Factor
0.018
Birefringence
δ = 0.008 - 0.009
Additional Information
Otherwise known by Sapphire, Ruby, or Carbuncle

Material articles have temporarily been disabled for renewal and polishing.
Variants and Types
Intrinsic
Intrinsic
Color: Colorless
Used for Bearings, Clock Jewels, Specialty Optics
Ruby
Ruby
Color: Red, Pink, Magenta
Fluorescence: Red, Pink (UVC)
Cause: Chromium Ions
Used for Lasers, Bearings, Clock Jewels
Padparadscha
Padparadscha
Color: Purple, Pink, Salmon, Orange
Cause: Iron and Chromium Ions
Typical Sapphire
Typical Sapphire
Color: Blue
Cause: Iron and Titanium Ions
Used for Bearings, Clock Jewels
Unnamed Variant
Unnamed Variant
Color: Green, Yellow, Orange
Cause: Iron Ions
Laser Sapphire
Laser Sapphire
Color: Red, Pink, Orange
Cause: Titanium Ions
Used for Laser Rods, Specialty Optics
Unnamed Variant
Unnamed Variant
Color: Blue, Cyan, Green
Cause: Cobalt Ions
'Alexandrite' Sapphire
'Alexandrite' Sapphire
Color: Purple, Red, Green, Blue, etc
Cause: Vanadium Ions
Effect: Color Change
Star Sapphire / Ruby
Star Sapphire / Ruby
Cause: Rutile (TiO2) Inclusions
Effect: Asterism / Cat's Eye
Production and Synthesis
Czochralski Method
Czochralski Method
Involves pulling a crystal (boule) upward from a molten solution. Produces some of the purest crystals but requires a cleanroom environment.
Verneuil Method
Verneuil Method
Involves sputtering molten material onto a boule similarly to plasma coating. Produces gem-grade quickly and cheaply, but often with defects.
Flux Method
Flux Method
Involves suspending a seed crystal near or inside flux with ingredients. Allows lower-temperature production. Sometimes produces gem-grade crystals.
Hydrothermal Method
Hydrothermal Method
Involves suspending a seed crystal into a high pressure / high temperature autoclave with liquid ingredients. Sometimes produces optics-grade ingots.
Kyropoulos Method
Kyropoulos Method
Derivative of the Czochralski method. Crystal grows into the feed material instead of being pulled. Can change the output purity and may be preferred.
Sintering and Annealing
Sintering and Annealing
An umbrella of methods involving heat treatment or controlled heating / burning to form solids and crystals. Often used for making polycrystalline media or annealing monocrystalline media.
Edge-Defined Film-Fed Growth
EDFFG
A method that involves pulling a seed through a vertical channel, with a die that feeds a film of molten material upward.
Zone Melting
Zone Melting
Involves passing cold / hot zones over a melt / seed to concentrate impurities in specific regions, while forming a monocrystalline ingot at the end of the path.
References
REFERENCES





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