Report on Alumino Silcate: Sillimanite

Essay by ChewyWookUniversity, Master'sA+, April 2005

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Aluminosilicate Mineral Profile

Mineral Name: Sillimanite

Chemical Formula: Al2SiO5

Silicate Structural Class: Nesosilicate

Diagnostics Properties:

Colour: White, Brown and Green

Transparency: Transparent to Translucent

Lustre: Silky or Vitreous

Specific Gravity: 3.2

Streak: White

Mohs Hardness: 7.5 in large crystals

Mineral Cleavage: Perfect. Good in 1 direction lengthwise


Type of Rock: Aluminium-rich metamorphic rocks

Temperature: Forms at temperatures greater than 550oC(2)

Pressure Field: Sillimanite is a polymorph with two other minerals: Kyanite and Andalusite. Sillimanite forms at high pressure (about 2.5 kilobars), Andalusite forms at higher temperatures but lower pressure (less than 2.5 kilobars) and Kyanite at high pressure (higher than 2.5 kilobars) but lower temperatures(3)

Geographic Localities: Brazil, England and other European sites

Main Uses: Sillimanite is mainly used in the manufacture of spark plugs and other forms of ceramic insulation. It can be used as a gemstone although this is rare and is more often used as mineral specimens.

Sillimanite: A compact chunk with obvious crystalline tendencies. Fibres are slightly curved and have a pearly lustre. (