Black Matrix Opal

Black matrix opal is a trade name for precious opal finely distributed through a host rock (matrix) with a dark background. The best-documented material is Andamooka matrix opal from South Australia: a cream to grayish white porous rock with specks of precious opal that is usually blackened by sugar-acid carbon treatment. Such stones are therefore commonly a treated natural material, not natural black opal; naturally dark matrix opal in black volcanic rock is also reported from Honduras and Nicaragua.