Rogue Gems, LLC carries a fine assortment of gem quality matrix boulder opal and vein boulder opal from Australia.
Opal has been found in many places, but today Australia is the primary source for gem quality opal. The stone was first discovered in Australia by a German mineralogist, Professor Johann Menge, in the 1840s.
Some of the most famous Australian fields are White Cliffs, Lightning Ridge, Coober Pedy, and Andamooka.
There are many different kinds of opal. The one we carry is boulder opal, which comes in two varieties: matrix boulder opal and vein boulder opal.
Matrix boulder opal consists of a porous sedimentary ironstone that contains minute cavities filled with precious opal. The dark brown ironstone polishes beautifully, and the opal sparkles as vivid pin flecks of color.
Vein boulder opal consists of ironstone, mudstone, or sandstone boulders that contain veins of opal from millimeters to centimeters thick.
Most of our boulder opal (both matrix and vein) comes from Winton in western Queensland. We also have a few pieces of opal from Koirot, which is southeast of Winton in Queensland.
Refractive Index: 1.44-1.46
Specific gravity: 1.98-2.20
Hardness: 5.5-6.5 (Mohs’s scale)
Crystal structure: opal is a non-crystalline form of silica