Andradite

Andradite is a species of the garnet group.

A nesosilicate.

Andradite includes three varieties: Melanite (black in color referred as titanian andradite), Demantoid (vivid green in color, one of the most valuable and rare stones), Topazolite (yellow-green, even rarer than demantoid)

Like other garnets, it crystallizes in cubic.

Andradite is named after the Brazilian mineralogist J.B. de Andrada e Silva (1763-1838).

Damantoid is named after its adamantine luster.

Andradite uses are in jewelry, making good gemstones.

Properties:

Category: Garnet

Formula: Ca3Fe2(SiO4)3

21,01% calcium; 19,52% iron; 14,73% silicon; 44,74% oxygen

33,11% CaO; 31,42% Fe2O3; 35,47% SiO2

Color: yellow, green-yellow to emerald green, dark green, brown, brownish red, brownish yellow ,gray black, black

Habit: commonly well-crystallized dodecahedra, trapezohedra or combinations, also granular to massive

Cleavage: none

Fracture: conchoidal to uneven

Tenacity: brittle

Density: 3,7-4,1; average 3,9

Hardness: 6,5-7,5 Mohs

Luster adamantine to resinous, dull

Streak: White

Transparent to translucent

Specific gravity: 3,859 calculated; measured 3,8-3,9

Forms in igneous and metamorphic rocks

Optical properties: isotropic, eakly anisotropic

Special properties: may show chatoyancy in Topazolite variety

Non-fluorescent

Common impurities: Ti, Cr, Al, Mg

Varieties:

Demantoid - transparent light to dark green to yellow green

Melanite - opaque black, Ti bearing (titanium)

Topazolite - transparent to translucent yellow, may show chatoyancy; resembling topaz

Bredbergite - green magnesian variety

Colophonite - a granular of brown, yellow-orange or redish garnet, usually andradite

Hydroandradite

Polyadelphite - a red brown, golden brown or yellow brown variety of manganoan andradite

Stanniferous andradite

Titanmelanite - black Ti bearing andradite also melanite, approaching schorlomite in composition

Titanoan andradite - brown coloured Ti bearing (titan)

Yttergranat - a rich Yttrium andradite

Mali garnet - garnet from Africa country of MAli, from green to yellow to brown (most often greenish-yellow)

Rainbow garnet - iridescent form of andradite garnet

Schorlomite - rare form of farnet rich in titanium, but scientifically classified as a individual mineral species

Associated minerals: Vesuvianite, Chlorite, Epidote, Spinel, Calcite, Dolomite, Magnetite, Sodalite.

Related minerals: Grossular, Uvarovite, Goldmanite, Hedenbergite, Pyroxferroite, Ferro-akermanite, Kirschsteinite, Tungusite, Ferro-actinolite, Ilvaite, Juigoldite.

Distinguishing similar minerals:

Almandine, Spessartine and Grossular - can be very difficult to distinguish but locality is often a good indicator.

Almandite can have a hardness of 7,5-8,5 and colorless streak; it is dark red, reddish-brown, black

Spessartine has hardness of 7; colorless streak, brown, orange, brownish-red, dark red, pink, yellow brown, yellow, gray black

Uvarovite - occurs in deeper colored green crystals as well in a different environment.

Colophonite, Polyadelphite

Andradite with brownish-red color on Sodalite