Hydrogrossular (Garnet)

     Hydrogrossular is just a calcium aluminum variety of Grossular Garnet with hydroxide (OH) partially replacing silica (SiO4). The identity of this member of the family that is hydro-garnetGrossular, Hydrogrossular, Hibschite and Katoite) depend regarding the level of replacement of hydroxide for silica.  Hydrogrossular is typically translucent to opaque, rarely clear, and found in different tones of green to bluish green, red, gray and white. The color that is green as a result of the presence of chromium and/or possibly iron. Pink Hydrogrossular is colored by the existence of manganese. Green Hydrogrossular may contain small dark gray to inclusions that are black. Opaque to Hydrogrossular that is translucent may similar to Jade but does not have any relationship to Jade. Hydrogrossular has been incorrectly referred to as Transvaal Jade or African Jade. 

      Hydrogrossular is found in massive practice that is crystal often intergrown in with Idocrase. Hydrogrossular is occasionally available as cabochons but seldom available as clean, transparent, faceted gemstones. These uncommon, clear gems are a beautiful yellowish green with small sleepiness similar to fine Prehnite gems. The supply that is primarily of beautiful gems is Achtaragda River mouth, Wilui River Basin, Saha Republic, Eastern-Siberian Region, Russia.  Sources for pink and green hydrogrossular are Canada, Russia, South Africa, and the United States. White Hydrogrossular is available in Burma and China.

Category:	Nesosilicate
Chemical Formula:	Ca3Al2(SiO4)3-x(OH)4x + Cr, Fe
	Calcium Aluminum Silicate Hydroxide + traces of chromium and/or iron
Crystallography:	Cubic – rhombic dodecahedron, icositetrahedron

 

Cleavage:	Indistinct
Fracture:	conchoidal
Hardness (Mohs):	7–7.5
Density:	3.57 to 3.73

 

Color:	green to bluish green, pink, white, gray
Transparency:	Transparent to opaque
Luster:	vitreous
Refractive Index:	1.734 to 1.759
Birefringence:	none
Pleochroism:	none