Grossular

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Grossular Garnet
Chemical composition Ca3Al2(SiO4)3

Calcium aluminum silicate

Crystal system Cubic
Habit Dodecahedra
Cleavage None
Hardness 7.0-7.5
Optic nature Isotropic
Refractive index 1.738-1.745
Birefringence None
Specific gravity 3.60-3.68
Lustre Vitreous

Diagnostics

Color

Green, yellowish-green, yellow-orange and pastel.

Inclusions

Hessonite: granular internal structure from numerous crystal inclusions, giving it an oily appearance.
Green grossular: rod-like or needle-like crystals.
Hydrogrossular: granular structure often with irregular black inclusions.

Refractometer

Hessonite and green grossular: 1.73-1.76 (singly refractive)
Hydrogrossular garnet: 1.70-1.73 (singly refractive)

Specific gravity

Grossular garnets sink in all common heavy liquids. Hydrogrossular garnet may sink slowly in methylene iodide.

Hessonite and green grossular garnet: 3.60-3.70
Hydrogrossular garnet: 3.35-3.55

Chelsea Colour Filter

Green stones may appear pinkish to red.

Varieties

Hessonite

Faceted Hessonite Garnet
Photo courtesy of Rick Martin, Art Cut Gems

Hessonite is the brownish-red to yellowish-orange variety.

Green grossular garnet

Faceted Mint Garnet
Photo courtesy of Ben Pfeiffer

Green grossular garnet is the bluish-green to yellowish-green variety. Within this group, Merelani Mint garnet is a grossular variety that is found in the Merelani Hills of Tanzania. It has emerged in the last few years with a bright pastel mint green color. Due to its limited availability it has remained mainly as a collector stone. The difference of it and Tsavorite is simply a matter of a lighter tone and saturation.

Hydrogrossular garnet

Hydrogrossular garnet cabochon
Photo courtesy of Rick Martin, Art Cut Gems

Hydrogrossular garnet is the green, pink, grayish-white to bluish variety of grossular.

Chrome grossular

Chrome grossular is a green variety of grossular.

Tsavorite

Faceted Tsavorite Garnet
Photo courtesy of Rick Martin, Art Cut Gems

Tsavorite (or tsavolite) is another green variety of chrome grossular.

Mali

Faceted Mali Garnet
Photo courtesy of Rick Martin,Art Cut Gems

Mali garnet is a yellow-green variety of grossular with a slight overlap in the grossular-andradite series.