Hydrogrossular

Big Photo

Tasmania, Australia
21.30 carats
© Giovanni Scapin 2015

An aggregate variety of grossular containing hydroxyl (OH), essentially the same as hibschite.

Colours vary from green to bluish green, sometimes pink, white or grey, translucent to opaque. The stones may have black spots or blotches.

Green varieties are often used as jade alternatives. It is also known as "Transvaal jade" or "African jade".
General Information
A variety or type of:Grossular, which is a variety of Garnet Group
Chemical Formula
Ca
 
3
Al
 
2
(SiO
 
4
)
 
3-x
(OH)
 
4x
- where 0 < x < 1.5
Gemdat.org, Management Team (2012)
Physical Properties of Hydrogrossular
Mohs Hardness7.5 to 8
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Specific Gravity3.25 to 3.40
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Optical Properties of Hydrogrossular
Refractive Index1.680 to 1.712
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004) Rose-redMore from other references
Optical CharacterIsotropic
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Colour
Colour (General)Rose-red, green
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Causes of ColourGreen ("Transvaal jade"), Cr3+ in octahedral coordination. Pink, Mn3+ in octahedral coordination
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyTranslucent,Opaque
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Crystallography of Hydrogrossular
Crystal SystemIsometric
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Further Information
Mineral information:Hydrogrossular information at mindat.org
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