Andamooka

Andamooka, South Australia and its opal

Andamooka is about 520 kilometres north of Adelaide in South Australia. The name itself means large waterhole in the local Aboriginal language.

The host rock for opal in this area is highly weathered Cretaceous claystone, called "kopi" by the miners. At the base of the kopi is a stratum of sand, pebbles and boulders.

The opal is found where this band meets the underlying band of grey-brown claystone, known as "mud." Andamooka opal is also found as matrix in cavities in the surrounding rock.

It is this porous matrix opal that is susceptible to colour enhancement by darkening of the background.

Crystal Opal