Grenades (silicates): Andradite

Diagnostic card.
On the picture. Varieties of andradite are characteristic black crystals of melanite. Below: dark green demantoid (Val Malenko, Italy).

Ca ₃ Fe ₂ (SiO ₄ ) ₃
Cubic amount of cubic zirconia
Hardness 6,5-7
Specific weight 3.74-4.1
Cleavage is absent
Cracked shell
Color yellow, blue, brown, black
Color in powder white
Shine from glass to semi-diamond

Andradite, a grenade group. Actually, andradite is unsuitable for jewelry purposes, but its varieties demantoid and topolite refer to jewelry stones.

Demantoid got its name due to a strong brilliance and a game similar to the brilliance and play of diamond (diamond). This is the most valuable mineral of the granite group. Its deposit is known in the Urals. It looks like grossular, peridot (chrysolite), green spinel, tourmaline, vesuvian, sometimes an emerald.

Melanite, an opaque, black, titanic variety of andradite. The deposit is being developed in Kaisershtuls (Germany). Used as mourning ornaments.

Topolit is a lemon-yellow or pinkish-yellow variety of andradite, similar to topaz, hence the name of the stone. Usually it is represented by small crystals. It occurs in Switzerland (Zermatt) and in the Italian Alps.

Andradite crystals are of the same type as other representatives of the group. First of all, characteristic rhombododecahedral forms of different colors are present.

The most common are black (melanite), yellow (topolite) and green (demantoid) differences, from transparent to almost opaque, glossy from glass to resin and even semi-diamond.

Cleavage - usually not observed, only on crystals from Jacobsberg (Sweden) installed sp. By (110). Individuality is noted by (110). Harakt. Allotment. - well-formed crystals, granular aggregates, dense masses. There is a continuous isomorphic series of andradite-grossular and, apparently, a series of andradite-uvarovite. In zonal garnets, the neighboring zones differ in composition.

Andradite from skarns of the Kassiar district (Canada) contains 0.9% SnO2. Spectroscopically in andradite from Arendal (Norway) found 1.26% B2O3. The helium content allows the use of andradite to determine the absolute age. Sometimes it contains rare earths: 2.73%.

Andradite is very hard, brittle, with a semi-fractured fracture, devoid of cleavage. Light brown, dark brown, brown, red, reddish-brown, reddish-brown, copper-brown, wine-red, greyish-green, less often green, yellow, greenish-brown, black. Depending on the color, a number of varieties are distinguished.

Topolite is a transparent variety of andradite of yellow, lemon-golden or honey-yellow color. Looks like the yellow topaz, hence its name. Topolite is extremely rare in the form of individual small grains (processed stones weighing 2-3 car are considered unique). Known in Switzerland and Italy. The hardness is 6.5-7. The density is 3.75-3.85 g / cm3. The refractive index is 1.84-1.89. It has a purely mineralogical significance as a collection stone.

Melanite (from the Greek "melas" - black) is a variety of andradite of black color, containing titanium. Melanite is known in Italy, the USA (Colorado), Germany, France, Uzbekistan (Tashkent region). Sometimes this stone is used in mourning ornaments. Especially dark varieties of melanite are called shorlomite and ivarit.

Diagnostic signs.
Andradite is resistant to acids. Relatively easy to fuse into a magnetic corona (magnetic depends on the iron content). After calcination it is easy to decompose in HCl with liberation of gel-like silica; The demantoid is dissolved in HCl without prior calcination.

Origin.
Andradite is a fairly common mineral; Is found mainly in contact deposits together with other silicates of calcium and iron. Melanite is characteristic of alkaline rocks, is known in contacts of alkaline granites with limestones. Topolite and demantoid are present most often in serpentinite rocks together with asbestos.

Application.
A variety of demantoid is of interest for jewelry business.

Andradite (topolite). Moussa Alpe, Val di Aala, Piedmont, Italy. Photo: © А.А. Evseev.

Andradit. Nazi Mountains, to the NW of Zlatoust, Ural, Russia. Photo: © А.А. Evseev.

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