Feature Gems & Gemology, Summer 1991, Vol. 27, No. 2

Treated Andamooka Matrix Opal

Matrix opal from Andamooka, in South Australia, is a precious opal-included porous rock that is commonly color enhanced (carbon impregnated) to imitate the highly prized black opal from Lightning Ridge in northern New South Wales, Australia. This material has been commercially available since the mid-1950s and is often referred to as “sugar treated." A basic sugar acid-carbonizing technique is used to carbonize, and thus darken, the cream-colored matrix of prepolished stones so that the play-of-color is more prominent. The carbon impregnator in treated Andamooka matrix opal can be readily identified with low-power magnification.