Andalusite (Al2O(SiO4))

Chemical Properties

gray, greenish, reddish, or bluish; hardness 7–7.5; used in dental cements and the glass industry, in enamels, ceramics, and as a paint filler [MER06] [HAW93]

Physical properties

Habit: acicular, blocky, prismatic, euhedral crystals.
Color: usually pink, white, rose, dark green, gray, brown, red, or green or with clouded inclusions.
Luster: vitreous (i.e., glassy).
Diaphaneity: transparent to translucent.
Cleavage: (110) distinct, (100) indistinct, (010) poor.
Fracture: uneven, splintery, brittle.
Streak: white.
Chemical: insoluble in strong mineral acids but attacked by molten alkali-metal hydroxides (e.g., NaOH) and carbonates (e.g., Na2CO3). Heated in Co(NO3 )2 give the Thénard blue color. Non fusible but transforms to sillimanite on heating.
Other properties: Unfusible but when heated above 1200°C transforms to a mixture of silica and mullite (Al6Si2O13). Dielectric constant of 8.28. Diamagnetic with a specific magnetic susceptibility of –10^–10 m³.kg^–1.
Occurrence: metamorphosed peri-aluminous sedimetary rocks.

Production Methods

It was estimated that in 1987, 90% of the kyanite produced in the United States was used in refractories, 55% of this for smelting and processing iron, 20% for smelting and processing nonferrous metals, and15% for refractories in glassmaking and ceramics.

Raw materials

Preparation Products