Andalusite - Encyclopedia

    Class : Silicates
    Subclass : Nesosilicates
    Crystal System : Orthorhombic
    Chemistry : Al2SiO5
    Rarity : Very common

Andalusite is the polymorph of kyanite and sillimanite. It is a common mineral, typical of aluminous rocks affected by regional metamorphism of low pressure or by contact metamorphism (cordierite-andalusite schists, hornfels, etc...) more rare in very aluminous granites and leucogranites and their pegmatites. It owes its name to its region of discovery : Andalusia, in Spain. It is presented in very coarse prisms with square sections, up to 20 cm long. Sometimes massive or with a radiated texture, most often stony and altered superficially in sericite, andalusite has a vitreous luster and is white to pink in color, sometimes greenish to purple or red. It can present a strong purple-green to green dichroism. Chiastolite is a variety with charcoal inclusions arranged in a cross pattern (main photo). Andalusite is the raw material and "ore" of mullite, the mineral at the base of the refractory products industry, in particular bricks, ceramics and porcelains resistant to high temperatures. The gemmy and strongly dichroic (green-red) varieties from California and Brazil are frequently cut as gemstones and used in jewelry.

0.90 ct faceted andalusite from Brazil
Dichroism of an andalusite of 0.63 ct from Brazil
21.60 ct chiastolite cabochon from China
36,00 ct chiastolite cabochon from China

Andalusite in the World

Giant andalusite crystals (1 m by 30 cm) are extracted from pegmatites from Mottlesrivier in South Africa, while large American andalusite crystals (30 cm) come from Maine (Standish, which also supplied pink gemmy ones) and Pennsylvania (Leiperville). Gemmy andalusite are typical of Brazil and Sri Lanka, where many deposits have produced magnificent centimetric gemmy crystals with red-purple to green dichroism : Santa Teresa, Chapada Diamantina, Novo Cruzeiro (Brazil), Ratnapura (Sri Lanka). Good crystals also come from the Cordoba region of Spain.

Andalusite in France

In France, andalusite is found in the Alps and also in Brittany (Glomel, Côte d'Armor) where this mineral (chiastolite variety), extraordinarily abundant, is exploited for the manufacture of refractories ; this site is currently the second largest producer of andalusite in the world with 60,000 tons per year extracted.

Faux et arnaques

No fake identified for this species.

Hardness : 6.5 to 7.5
Density : 3.13 to 3.21
Fracture : Uneven to sub-conchoidal

Streak : White

TP : Translucent to transparent
IR : 1.629 to 1.650
Birefringence : 0.009 to 0.010
Optical character : Biaxial -
Pleochroism : Green to red
Fluorescence : Green to yellow

Solubility : Hydrofluoric acid

Magnetism : None
Radioactivity : None


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