Wollastonite is calcium silicate (CaSiO₃) which forms as aggregates of needle-shaped crystals. Crystals with high aspect ratio (long needle shapes) are used as an asbestos fibre substitute, and for reinforcing in thermoplastics and thermoset polymers. Wollastonite with a low aspect ratio is used as a general filler, and in some ceramic bodies where its low coefficient of thermal expansion reduces shrinkage, cracking, and crazing. Estimated world production is ~300 000 t/year, with consumption roughly equally divided between USA, Europe and Asia. USA and India supply ~90% of total sales of high aspect ratio product. China and Finland are also major wollastonite producers. There is no production in Australia and all requirements are imported.

At the Ethiudna deposit, 20 km north-northwest of Manna Hill in the State’s northeast, wollastonite occurs in deformed diopside marble within metasediments of the Willyama Supergroup. The marble formed from impure limestone during contact metamorphism caused by 1579 Ma granite which crops out at Crockers Well, 2 km to the north. A resource of ~1 Mt containing 40% wollastonite has been identified in three orebodies in the keel of a tightly refolded syncline. Several other minor occurrences occur in this stratigraphic unit nearby. The deposit is held under lease by Minerals Corporation Ltd, but there has been no commercial production.

Deformed wollastonite marble, Ethiudna

Additional Reading

Crooks, A.F., 1999. Wollastonite in South Australia. South Australia. Department of Primary Industries and Resources. Report Book, 99/16.