Grossular

Grossular
Grossular dodecahedron, 7 mm across, from Coahuila, Mexico
General
Category	Nesosilicate
Formula (repeating unit)	Ca3Al2(SiO4)3
IMA symbol	Grs[1]
Strunz classification	9.AD.25
Crystal system	Cubic[2]
Crystal class	Hexoctahedral (m3m) H-M Symbol: (4/m 3 2/m)
Space group	Ia3d
Identification
Color	light to dark green, light to dark yellow to reddish brown, brown, orange, red, yellow, green, white, occasionally translucent to opaque pink. It is also but rarely found in colorless form[2]
Cleavage	none
Fracture	conchoidal to uneven[2]
Mohs scale hardness	6.5 to 7[2]
Luster	greasy to vitreous[2]
Streak	Brown
Specific gravity	3.61 (+.15/−.04)
Polish luster	vitreous[2]
Optical properties	Single refractive, often anomalous double refractive[2]
Refractive index	1.740 (+.12/−.04)[2]
Birefringence	none
Pleochroism	none
Dispersion	.028
Ultraviolet fluorescence	near colorless to light green – inert to weak orange in longwave and weak yellow-orange in shortwave; yellow – inert to weak orange in longwave and shortwave[2]
Absorption spectra	Hessonite sometimes shows bands at 407 and 430 nm
Major varieties
Hessonite	yellow-red to reddish-orange
Tsavorite	intense green to yellowish green
Leuco-garnet	transparent and colorless[3]
Rosolite	translucent to opaque pink grossularite crystals in marble from Mexico

Grossular is a calcium-aluminium species of the garnet group of minerals. It has the chemical formula of Ca₃Al₂(SiO₄)₃ but the calcium may, in part, be replaced by ferrous iron and the aluminium by ferric iron. The name grossular is derived from the botanical name for the gooseberry, grossularia, in reference to the green garnet of this composition that is found in Siberia. Other shades include cinnamon brown (cinnamon stone variety), red, and yellow. Grossular is a gemstone.

In geological literature, grossular has often been called grossularite. Since 1971, however, use of the term grossularite for the mineral has been discouraged by the International Mineralogical Association.^[4]