Garnet

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Garnet
General
Category	Nesosilicate
Formula	The general formula X3Y2(SiO4)3
IMA symbol	Grt[1]
Crystal system	Isometric
Crystal class	${\displaystyle 4/m{\bar {3}}2/m}$
Space group	Ia3d
Identification
Color	virtually all colors, blue is 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
Diaphaneity	Can form with any diaphaneity, translucent is common
Specific gravity	3.1–4.3
Polish luster	vitreous to subadamantine[2]
Optical properties	Single refractive, often anomalous double refractive[2]
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

Garnets ( /ˈɡɑːrnɪt/) are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.

Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, defining distinct species. These species fall into two primary solid solution series: the pyralspite series (pyrope, almandine, spessartine), with the general formula [Mg,Fe,Mn]3Al2(SiO4)3; and the ugrandite series (uvarovite, grossular, andradite), with the general formula Ca3[Cr,Al,Fe]2(SiO4)3. Notable varieties of grossular include hessonite and tsavorite.