Garnet

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Garnet
General
Category	Nesosilicate
Formula (repeating unit)	The general formula X3Y2(SiO4)3
Identification
Color	virtually all colors, blue very rare
Crystal habit	Rhombic dodecahedron or cubic
Cleavage	Indistinct
Fracture	conchoidal to uneven
Mohs scale hardness	6.5–7.5
Luster	vitreous to resinous
Streak	White
Specific gravity	3.1–4.3
Polish luster	vitreous to subadamantine[1]
Optical properties	Single refractive, often anomalous double refractive[1]
Refractive index	1.72–1.94
Birefringence	None
Pleochroism	None
Ultraviolet fluorescence	variable
Other characteristics	variable magnetic attraction
Major varieties
Pyrope	Mg3Al2Si3O12
Almandine	Fe3Al2Si3O12
Spessartine	Mn3Al2Si3O12
Andradite	Ca3Fe2Si3O12
Grossular	Ca3Al2Si3O12
Uvarovite	Ca3Cr2Si3O12

A garnet /ˈɡɑːrnət/ is one kind of silicate mineral. There are many different kinds of garnets, containing different metals. Crystals of garnet are often large and pretty. Their most common color is red or purple, but they can be found in almost all colors and are often used in jewelry. In the United States, garnet is the birthstone for people born in the month of January.

1. ↑ ^{1.0 1.1} Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6