Andalusite

What is Andalusite?
Andalusite is a rock-forming mineral that is mined for use in high-temperature refractories. Gem-quality specimens are cut into faceted gems and cabochons.

Andalusite forms during the regional metamorphism of shale. It is found in schist and gneiss at some present and ancient convergent plate boundaries where the rocks have been exposed to the temperatures and pressures needed for its formation. In these rocks, andalusite is often associated with kyanite and sillimanite.

Andalusite also forms during the contact metamorphism of argillaceous rocks. In this situation, it can form within the metamorphosed rock or in veins and cavities within the igneous rock. It can be associated with cordierite in hornfels, granite, and granitic pegmatite.

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Physical Properties of Andalusite

 * Chemical Classification
 * Silicate
 * Color
 * Reddish brown, olive green, white to gray
 * Streak
 * White
 * Luster
 * Vitreous
 * Diaphaneity
 * Transparent to nearly opaque
 * Cleavage
 * Good
 * Mohs Hardness
 * 6.5 to 7.5
 * Specific Gravity
 * 3.17
 * Diagnostic Properties
 * Crystal form, associated minerals, strongly pleochroic, symmetrical inclusions
 * Chemical Composition
 * Al2SiO5
 * Crystal System
 * Orthorhombic
 * Uses
 * Used to manufacture high-temperature porcelain of spark plugs; used to make high-temperature ceramics used in furnaces, kilns, incinerators; high-quality crystals are often used as gemstones.
 * }
 * Diagnostic Properties
 * Crystal form, associated minerals, strongly pleochroic, symmetrical inclusions
 * Chemical Composition
 * Al2SiO5
 * Crystal System
 * Orthorhombic
 * Uses
 * Used to manufacture high-temperature porcelain of spark plugs; used to make high-temperature ceramics used in furnaces, kilns, incinerators; high-quality crystals are often used as gemstones.
 * }
 * Uses
 * Used to manufacture high-temperature porcelain of spark plugs; used to make high-temperature ceramics used in furnaces, kilns, incinerators; high-quality crystals are often used as gemstones.
 * }