Grossular
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.
| Grossular | |
|---|---|
Grossular dodecahedron, 7 mm across, from Coahuila, Mexico | |
| General | |
| Category | Nesosilicate |
| Formula (repeating unit) | Ca3Al2(SiO4)3 |
| IMA symbol | Grs |
| Strunz classification | 9.AD.25 |
| Crystal system | Cubic |
| 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 |
| Cleavage | none |
| Fracture | conchoidal to uneven |
| Mohs scale hardness | 6.5 to 7 |
| Luster | greasy to vitreous |
| Streak | Brown |
| Specific gravity | 3.61 (+.15/−.04) |
| Polish luster | vitreous |
| Optical properties | Single refractive, often anomalous double refractive |
| Refractive index | 1.740 (+.12/−.04) |
| 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 |
| 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 |
| Rosolite | translucent to opaque pink grossularite crystals in marble from Mexico |
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.
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