The perlite occurrence is located at the headwaters of Coates Creek, 10 kilometres west of Port Louis.

The area is underlain by sub-aerial dacitic to rhyolitic flows/domes, breccias and pyroclastics of the Upper Oligocene to Lower Pliocene Masset Formation, which form a plateau volcanic sequence up to 5 kilometres thick dipping gently to the east.

Perlite occurs as a flow-like mass in rhyolite units of the Tartu Facies. The perlite is a "pearly" lustered acidic to sub- acidic volcanic glass with a deep blue "serpentinitic" appearance on fresh surface and grey to brown-black on weathered surface.

The perlite forms two possibly unconnected bodies. The southern body strikes north-south for 400 metres and is 100 metres thick and 50 metres wide. The northern body, 250 metres long, 100 metres wide, and about 100 metres thick, strikes east-west.