Opalised Serpentine occurs in the Pilbara region of Western Australia near the town of Newman which is approximately 1,100 kms north of the capital, Perth.
The geological setting of the occurrence is that of an ultramafic intrusion into an area of granite-greenstone of Archaean age(>2500Ma)
The intrusion consists of serpentinite that has also produced chrysoprase, chalcedony & common opal. These rock types along with the opalised serpentine occur in the weathered , silicified cap rock.
It is believed that original weathered serpentinite has been replaced through processes of silica deposition and the areas of chrome chalcedony within the opalised serpentine represents a whole-rock replacement or psuedomorph.
Chromium which is responsible for the green colouration, has originated from the existence of chromite within the serpentinite.