Mineral - Corundum
Corundum
Chemical Properties
Mineral Class
Oxides and Hydrxides
Toxicity
none
Formula
Al₂O₃
Unit Cell
a=4.75 c=12.98 Z=6
Physical Properties
Hardness
9
Streak
white
Density
Heavy (3,5-6)
Cleavage
Fracture
conchoidal,
uneven
Tenacity
Brittle
Optical Properties
Color
whiteblackbrowngrayredorangeyellowgreenbluecolorless
Birefringence
0.009
Luster
Vitreous,
Greasy,
Adamantine
Transparency
translucent,
transparent,
opaque
Pleochroism
Geomineralogical Properties
Crystal System
trigonal
Point Group
ditrigonal-scalenohedral - 3 m
Space Group
R 3 c (167)
Habit
blocky, dipyramidal, prismatic, columnar, Scalenohedron, tabular, barrel-shaped
Formation
(1) Magmatic, through crystallization from SiO2-undersaturated melts (such as syenites or nepheline syenites) and as an accessory in Al-rich plutonites.
(2) Metamorphic, through contact or regional metamorphism of Al-rich protoliths (pelites, bauxites) under amphibolite to granulite facies P-T conditions.
(3) Metasomatic, through desilicification of aluminum-bearing rocks in contact with silica-poor intrusions or fluids.
Paragenesis
Twinning
Contact twins after {102}
Rarity
Common
Synonyms
Corundum, Ruby, Sapphire
Groups and Members
Hematite-Group