Andradite
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| Andradite | |
|---|---|
 The black mineral is Andradite, (Melanite)
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| General | |
| Category | Mineral |
| Chemical formula | Ca3Fe2Si3O12 |
| Identification | |
| Color | yellow, green, brown, black |
| Crystal system | cubic [1] |
| Cleavage | none |
| Fracture | conchoidal to uneven [1] |
| Mohs Scale hardness | 6.5 to 7 [1] |
| Luster | vitreous |
| Polish luster | vitreous to subadamantine [1] |
| Refractive index | 1.888 (+.007 -.033) [1] |
| Optical Properties | Single refractive, often anomalous double refractive [1] |
| Birefringence | none [1] |
| Dispersion | .057 [1] |
| Pleochroism | none [1] |
| Ultraviolet fluorescence | inert [1] |
| Absorption spectra | demantoid - 440nm band or complete absorption at 440nm and below, may also have lines at 618, 634, 685, 690nm [1] |
| Specific gravity | 3.84 (+/-.03); melanite - 3.90 (+/- .20) [1] |
| Major varieties | |
| Demantoid | transparent light to dark green to yellow-green |
| Melanite | opaque black |
| Topazolite | transparent to translucent yellow, may show chatoyancy |
Andradite is a species of the Garnet Group. It is a nesosilicate, with formula Ca3Fe2Si3O12. [1]
Andradite includes 3 varieties:
- Melanite: Black in color, usually not cut as a gemstone.
- Demantoid: Vivid green in color, one of the most valuable and rare stones in the gemological world.
- Topazolite: Yellow-green in color and sometimes of high enough quality to be cut into a faceted gemstone.
- Andradite also is found in rarely colorless.
Andradite was named after the Brazilian mineralogist José Bonifácio de Andrade e Silva (1763-1838). It has a hardness of 6.5 to 7.[2][1] Associated minerals are micas, diopside, chlorite, and serpentine. It is found in Italy, the Ural Mountains of Russia, Arizona and California.
[edit] External links
[edit] References
- ^ a b c d e f g h i j k l m n Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN:0-87311-019-6
- ^ Andradite Webmineral website, accessed January 23, 2007
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