Garnet

Garnet
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
Optical properties	Single refractive, often anomalous double refractive
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.

Garnet Media

A sample showing the deep red color garnet can exhibit.
Almandine in metamorphic rock
Spessartine (the reddish mineral)
Grossular garnet from Quebec, collected by Dr John Hunter in the 18th century, Hunterian Museum, Glasgow
Grossular on display at the U.S. National Museum of Natural History. The green gem at right is a type of grossular known as tsavorite.
Main garnet producing countries
Garnet var. Spessartine, Putian City, Putian Prefecture, Fujian Province, China
c. 8th century AD, Anglo-Saxon sword hilt fitting – gold with gemstone inlay of garnet cloisonné. From the Staffordshire Hoard, found in 2009, and not fully cleaned
Pendant in uvarovite, a rare bright-green garnet
Crystal structure of pyrope garnet. White spheres are oxygen; black, silicon; blue, aluminium; and red, magnesium.