Sillimanite, kyanite and andalusite, known collectively as the sillimanite minerals, are anhydrous aluminium silicates with the general formula Al2SiO5. All three minerals are transparent to opaque, have a vitreous lustre, and are highly refractory. Their main industrial use is in the manufacture of refractories, which accounts for 90% of all consumption. When calcined, all three minerals alter to silica glass and mullite (3Al2O3.2SiO2 or 2Al2O3SiO2).
Kyanite, sillimanite and andalusite are widespread products of metamorphism, typically found in aluminous metamorphic rocks and their weathered products. All three are commonly found in schist and gneiss along with biotite, muscovite, feldspar, garnet and occasionally hornblende. Their presence is often used as an indicator of metamorphic facies.
Geological environments favourable to the occurrence of andalusite and sillimanite in Victoria are:
- the Omeo Metamorphic Complex and the Kuark Metamorphics, in eastern Victoria
- the Glenelg River Metamorphic Complex, in western Victoria.
Recorded occurrences of kyanite in Victoria are rare and, although rocks containing sillimanite and andalusite are more extensive, there are no records of economic deposits of any of these minerals.
- Industrial minerals and rocks of Victoria - Geological Survey of Victoria Report 102
- Geological History of Victoria
- Victoria's Minerals, Petroleum and Extractives Industries - Statistical Review
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