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Chemical Composition : Al2SiO5
Hardness : 6.5 – 7.5
Specific Gravity (Density) : 3.13 – 3.17 (g/cm3)
Refractive Index : 1.629 – 1.650 Biaxial ( – ) or ( + )
Andalusite is strongly pleochroic showing colors of olive green to brick red. Its strong pleochroism is very distinctive and extremely attractive as a faceted gem. Andalusite trimorphous with Kyanite and Sillimanite. Trimorphous refers to a mineral that shares the same chemistry but a different crystal structure with two other minerals. Andalusite has two other interesting varieties. One is called Chiastolite. It is usually opaque and contains black carbon inclusions which are arranged in regular symmetrical shapes, usually in the form of a cross or X. Chiastolite cut in cross section and polished makes for very unique and attractive cabochons, beads or pendants showing a well-formed black cross on a gray or brown background. The name Chiastolite is from the Greek chiastos meaning arranged diagonally, because the pattern of carbon inclusions resembles the Greek letter Chi, which is written X. The other variety of Andalusite is Viridine which is a rich, grass green color due to its manganese content. Viridine gets its name from the Latin word viridis for green. A current source of fine Andalusite crystals is the Santa Teresa district, Espirito Santo, Brazil. Chiastolite and Viridine are also found in Brazil.
Andalusite is widespread. Some localities for good crystals follow. From Hornachuelos, near Córdoba, Córdoba Province, Spain. On the Lisens Alp, Selraintal, Tirol, Austria. At Gefrees, Bodenmais, and elsewhere in Bavaria, Germany. From the Claggau quarry, County Galway, Ireland. In the USA, from Lancaster, Worcester County, Massachusetts; Leiperville, Delaware County, Pennsylvania; around Custer, Custer County, South Dakota; in California, from Fresno, Fresno County, near Ogilby, Cargo Muchacho Mountains, Imperial County, and near Daltons Ranch, Madera County. From Mt. Howden, Bimbowrie, South Australia. At Nawalapitiya, Sri Lanka. Gem crystals from the Santa Teresa district, Espírito Santo, Brazil.