The rocks at Catpund were originally lavas rich in the mineral olivine that were erupted onto the floor of the Iapetus Ocean about 580 million years ago. They were metamorphosed when hot fluids circulated through them as the ocean closed, altering the olivine to serpentine and ultimately to talc. Rock composed mainly of talc is often referred to as soapstone or steatite. In Shetland the old Norse word kleber is used. Soapstone feels soapy to the touch and is easy to carve because talc is the softest mineral known to man. When heated the rock becomes stronger and non-porous. These properties made kleber an important resource throughout Shetland's history and it was of particular value to the Norse inhabitants of the islands. They quarried it extensively to produce domestic items including bake plates, loom weights, fishing weights, oil lamps and spindle whorls, which have been found at many sites throughout the islands. Catpund is the largest soapstone quarry in Shetland and is a Scheduled Archaeological Monument. Chisel marks and numerous hollows where bowls were fashioned and extracted can be seen within the fenced area. The hillside is dotted with further workings and mounds that represent former spoil heaps.