The central part of Hawkesbury Island is underlain by amphi- bolite, biotite schist, kyanite-staurolite-almandine mica schist, sericite-epidote schist, fine-grained sillimanite-quartz-plagioclase gneiss, graphitic plagioclase schists, quartzite, and crystalline limestone.

On Hawkesbury Island the kyanite-staurolite-almandine schists exposed contain up to 20 per cent almandine garnet and up to 20 per cent kyanite (Money, 1959). The kyanite may be extremely coarse with blades that reach 20 centimetres by 1 centimetre in size. The indi- vidual kyanite-staurolite-almandine schist units vary from a metre to over 30 metres in thickness and are traceable along strike for up to 2 kilometres (refer to Hawkesbury Island Garnet, 103H 057).

Sillimanite is reported from only one locality on Hawkesbury Island near Fishtrap Bay (refer to Area 2, Figure 10, Open File 1988- 26). At this locality, the sillmanite is present as rounded knots in gneiss and comprises up to 15 per cent of the rock (Money, 1959).