Grossular
| Grossular | |
|---|---|
Grossular dodecahedron, .7 cm across, from Coahuila, Mexico
|
|
| General | |
| Category | Nesosilicate |
|
Formula (repeating unit) |
Ca3Al2(SiO4)3 |
| 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, occasionally translucent to opaque pink. It is also but rarely found in colorless form |
| Cleavage | none |
| Fracture | conchoidal to uneven |
| Mohs scale hardness | 7 to 7.5 |
| Luster | greasy to vitreous |
| 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 430nm |
| Major varieties | |
| Hessonite | yellow-red to reddish-orange |
| Tsavorite | intense green to yellowish green |
| Leuco-garnet | transparent and colorless |
| Xalostocite | translucent to opaque pink grossularite crystals in marble |
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 should not be called grossularite, grossularite was once a type of rock.
Hessonite or Cinnamon Stone, is a more common variety of grossular with the general formula: Ca3Al2Si3O12. The name comes from the Ancient Greek: ἣσσων (hēssōn), meaning inferior; an allusion to its lower hardness and lower density than most other garnet species varieties.
It has a characteristic red color, inclining to orange or yellow, much like that of zircon. It was shown many years ago, by Sir Arthur Herbert Church, that many gemstones, especially engraved gems (commonly regarded as zircon), were actually hessonite. The difference is readily detected by the specific gravity, that of hessonite being 3.64 to 3.69, while that of zircon is about 4.6. Hessonite has a similar hardness to that of quartz (being about 7 on the mohs scale), while the hardness of most garnet species is nearer 7.5.
Hessonite comes chiefly from Sri Lanka and India where it is found generally in placer deposits, though its occurrence in its native matrix is not unknown. It is also found in Brazil and California.
...
Wikipedia