An Australian boulder opal split is a boulder opal vein split
into 2 pieces through the vein of opal.
Australian boulder opal is precious opal found in cracks or cavities in an ironstone rock.
When an opal vein in a boulder is thick enough, a groove of about one millimeter deep is done around the stone into the opal seam with a diamond saw blade.
The stone is then split open.
It results in 2 stones instead of one, with almost identical colour play, fitting together.
Depending on the size of the original stone, a pair of earrings, or a full set of earrings, pendant and a ring can be obtained with matching opal colours.