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Grossular



Grossular

A grossular crystal group
General
CategoryMineral
Chemical formulaCa3Al2(SiO4)3
Identification
Colorlight to dark green, light to dark yellow to reddish brown, occasionally translucent to opaque pink. It is also but rarely found in colorless form [1]
Crystal systemcubic [1]
Cleavagenone
Fractureconchoidal to uneven [1]
Mohs Scale hardness7 to 7.5 [1]
Lustergreasy to vitreous [1]
Polish lustervitreous [1]
Refractive index1.740 (+.12 -.04) [1]
Optical PropertiesSingle refractive, often anomalous double refractive [1]
Birefringencenone
Dispersion.028
Pleochroismnone
Ultraviolet fluorescencenear 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 [1]
Absorption spectraHessonite sometimes shows bands at 407 and 430nm
Specific gravity3.61 (+.12 -.04)
Major varieties
Hessoniteyellow-orange to reddish-orange
Tsavoriteintense green to yellowish green
Leuco-garnettransparent and colorless [2]
Xalostocitetranslucent to opaque pink grossularite crystals in marble

Grossular, also incorrectly called grossularite, is a calcium-aluminium mineral species of the garnet group with the formula Ca3Al2(SiO4)3,[1] though 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.  

Additional recommended knowledge

The more common variety of grossular is called hessonite from the Greek meaning inferior, because of its inferior hardness to zircon, which the yellow crystals resemble. Grossular is found in contact metamorphosed limestones with vesuvianite, diopside, wollastonite and wernerite.

A highly sought after variety of gem garnet is the fine green Grossular garnet from Kenya and Tanzania called tsavorite. This garnet was discovered in the 1960s in the Tsavo area of Kenya, from which the gem takes its name.

 

Viluite is a variety name of grossular, that is not a recognized mineral species.[3] It is usually olive green though sometimes brownish or reddish, brought about by impurities in the crystal. Viluite is found associated with and is similar in appearance to vesuvianite, and there is confusion in terminology as viluite has long been used as a synonym for wiluite, a sorosilicate of the vesuvianite group. This confusion in nomenclature dates back to James Dwight Dana.[4] It comes from the Vilyuy river area in Siberia.

Grossular is known by many other names, and also some misnomers;[5] colophonite - coarse granules of garnet[6], ernite, gooseberry-garnet - light green colored and translucent,[7] kalkthongranat, kanelstein, olyntholite/olytholite, pechgranat, romanzovite, and tellemarkite. Misnomers include;[2] South African jade, garnet jade, Transvaal jade, and African jade.

References

  1. ^ a b c d e f g h i j Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. ^ a b Grossular The Mineral and Gemstone Kingdom, accessed online January 25, 2007
  3. ^ Viluite Mindat database
  4. ^ The System of Mineralogy of James Dwight Dana. Descriptive Mineralogy By James Dwight Dana, Edward Salisbury Dana, 1892, p. 479-80
  5. ^ Grossular Mindat mineral database, accessed January 25, 2007
  6. ^ Colophonite The Free Dictionary, accessed online January 25, 2007
  7. ^ Gooseberry Garnet WordWeb Online
  • Mineral Galleries grossular data
  • Webmineral data
  • Mindat grossular data
  • Mineral Data Publishing
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Grossular". A list of authors is available in Wikipedia.
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