Almandine

ALMANDINE (Late Latin "alamandina", "alabandina", from the name of the "Alabanda" ancient city in the Asia Minor * EN: almandine; DE: Almandin; FR: almandine; ES: almandina; RU: альмандин) is the mineral of the group of the garnets, Fe3Al2[SiO4]3. It is associated by the continuous isomorphic series with pyrope and spessartine. The common admixtures are: MnO approximately 1.5%, MgO up to 5.3%, CaO approximately 2%. The size of the crystals is from 5.6 millimetres to 5 centimetres. The hardness is 7.0-7.5. The density is 3800-4300 kilograms per cubic metre. The colour is violet-red, less often dark brown, saturated red.

The types of the deposits are: the effusive rocks of the intermediate and acidic constitution, the granitic pegmatites of the muscovitic and rare metallic formations, the ultra-acidic granites, crystalline schists and gneisses. The almandine in the pegmatites and granites is usually enriched by Mn, in the metamorphic rocks is enriched by Mg.

The main industrial type of the deposits is the eluvial, alluvial, and littoral placer deposits, which have formed themselves as the result of the destruction of the garnet-containing crystalline schists (Sri Lanka, India, Brazil, USA; in the USSR, Karelia). The transparent crystals of almandine belong to the precious stones of the IV order, while fine-grained separations and opaque varieties are used as the abrasive raw materials.