Andradite

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Andradite Garnet
Chemical composition Ca3Fe2(SiO4)3

Calcium Iron Silicate

Crystal system Cubic
Habit Dodecahedra
Cleavage None
Hardness 6.5
Optic nature Isotropic
Refractive index 1.85-1.89
Birefringence None
Specific gravity 3.85
Lustre Vitreous to adamantine
Iridescent Andradite Garnet
Photo courtesty of The Gem Trader


Diagnostics

Color

Green, yellow-green and black.

Inclusions

  • Fine curving asbestos fibres in a radiating pattern ("horse-tail") in demantoid.

Refractometer

With an RI of about 1.89, the readings are outside the limit of the standard gemological refractometer.

Specific gravity

Sinks in all common heavy liquids.

Chelsea Color Filter

Demantoid appears reddish or pinkish.

Spectroscope

Demantoid has a specific pattern due to iron and chromium.

Dispersion

The dispersion in andradite garnets is high (0.057) and is partially masked by body color.

Varieties

Demantoid

Demantoid is the green variety of andradite.

Melanite

Melanite is the black, opaque variety which is mostly used in mourning jewelry.

Topazolite

Topazolite is the lemon yellow variety of andradite.

Grandite

Faceted Grandite
Photo courtesy of
Wild Fish Gems

Grandite is a brownish variety of grossular-andradite and has lower values compared to the other varieties of andradite. It's name is often used to indicate the whole grossular-andradite intermediate series. Refractive index: 1.780-1.82


Inclusion images

Horsetail inclusions in Russian demantoid garnet.
Photo courtesy of Apsara.co.uk
Horsetail inclusions in Russian demantoid garnet.
Photo courtesy of Apsara.co.uk
Horsetail inclusions in Russian demantoid garnet.
Photo courtesy of Apsara.co.uk

Horsetail inclusions in Russian demantoid garnet.
Photo courtesy of Apsara.co.uk
Horsetail inclusions in Russian demantoid garnet.
Photo courtesy of Apsara.co.uk
Horsetail inclusions in Russian demantoid garnet.
Photo courtesy of Apsara.co.uk