Antigorite from Rowland Flat, South Australia: asbestiform character

Asbestiform antigorite from Rowland Flat near Adelaide in South Australia is shown by scanning and transmission electron microscopy to consist of bundles of [010] fibres. Defects combine with grain boundaries to define flattened fibres from 20 nm to 10 mm in width. Splitting along these microstructures leads to the asbestiform character. Within any individual crystal there are commonly two or more polysomes, indicating slight compositional variation within the crystal. Intergrowths of different polysomes are also associated with characteristic microstructures including [100] modulation dislocations. Also, the antigorite structures are everywhere incommensurate with polysome M ranging from 13 to 17. The fibrous habit appears related to the replacement reaction through which the antigorite phase has grown.