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Andradite



Andradite

The black mineral is Andradite, (Melanite)
General
CategoryMineral
Chemical formulaCa3Fe2(SiO4)3
Identification
Coloryellow, green, brown, black
Crystal systemcubic [1]
Cleavagenone
Fractureconchoidal to uneven [1]
Mohs Scale hardness6.5 to 7 [1]
Lustervitreous
Polish lustervitreous to subadamantine [1]
Refractive index1.888 (+.007 -.033) [1]
Optical PropertiesSingle refractive, often anomalous double refractive [1]
Birefringencenone [1]
Dispersion.057 [1]
Pleochroismnone [1]
Ultraviolet fluorescenceinert [1]
Absorption spectrademantoid - 440nm band or complete absorption at 440nm and below, may also have lines at 618, 634, 685, 690nm [1]
Specific gravity3.84 (+/-.03); melanite - 3.90 (+/- .20) [1]
Major varieties
Demantoidtransparent light to dark green to yellow-green
Melaniteopaque black
Topazolitetransparent to translucent yellow, may show chatoyancy

Andradite is a species of the Garnet Group. It is a nesosilicate, with formula Ca3Fe2Si3O12. [1]

Additional recommended knowledge

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.

References

  1. ^ 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
  2. ^ Andradite Webmineral website, accessed January 23, 2007

 

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Andradite". A list of authors is available in Wikipedia.
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