Chiastolite

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Description

Chiastolite

Mineral Species Andalusite
Mineral Group silicate
Composition Al2SiO5
Origin Hunan Province, China
dimension 3.5 x 3 x 1cm
weight 30g

Andalusite was named after the area where deposits were first found – in Andalusia (at Almeria on the southern coast of Spain). Before true andalusite was discovered, its variety, chiastolite (name derived from resemblance to the Greek letter khi) was already known from the city of Santiago de Compostella, to which pilgrimages were often made. This variety was used for the manufacture of memorial objects, the so-called ‘stone of the Cross’. Chiastolites are, basically, crystals of andalusite arranged in regular directions and filled with carbonaceous substances. Otherwise andalusite forms columnar or stalk-like crystals or stalky and leafy aggregates. It occurs in gneisses, in metamorphosed contact slates resembling phyllites (chiastolitic slates) and in pegmatites. In many deposits it is accompanied by staurolite or corundum. Industrially important deposits are in Kazakhstan and in California. The other most noted deposits are in Austria, at Murzinka in the Urals, in Brazil and in Bimbowrie in South Australia. Andalusite is used in the manufacture of refractory materials and special porcelains. The variety from Brazil is used as a less common precious gemstone.
The minerals disthene and sillimanite have the same chemical composition. Disthene is triclinic and sillimanite orthorhombic. Disthene received its name from the Greek di (`double’) and sthenos (`strength’), on account of its conspicuously different hardness in different directions. The hardness of its tabular crystals is 4 5 along the prism but 7 across. The blue variety is called kyanite, the white to grey variety rhaeticite. Sillimanite is commonly finely fibrous to acicular, and is coloured white. When mixed with quartz, it is called fibrolite.

Additional information

Weight 30 g
Dimensions 3.5 x 3 x 1 cm