The company's quarry at Mt Sylvia exploits a partially altered very hard fine olivine basalt.This resource is unique in that it was created by lava flowing into a fresh water crater lake in which an underlying diatomaceous earth deposit had already been laid down within the crater of an older basalt intrusion. The interaction of the later lava inflow and water created volcanic glass at the lava-water interface. This glass devitrified over time to a smectite clay in combination with other amorphous minerals. This geological process is called palagonisation.