Garnet

This article's lead section may be too short to adequately summarize the key points. Please consider expanding the lead to provide an accessible overview of all important aspects of the article. (January 2024)

Garnet
General
Category	Nesosilicate
Formula (repeating unit)	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.

All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different species are pyrope, almandine, spessartine, grossular (varieties of which are hessonite or cinnamon-stone and tsavorite), uvarovite and andradite. The garnets make up two solid solution series: pyrope-almandine-spessartine (pyralspite), with the composition range [Mg,Fe,Mn]₃Al₂(SiO₄)₃; and uvarovite-grossular-andradite (ugrandite), with the composition range Ca₃[Cr,Al,Fe]₂(SiO₄)₃.