Australian boulder opal split

An Australian boulder opal split is when an opal vein in a boulder opal has been split into 2 pieces.
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, it can be hit hard with a hammer, and the stone will split in two pieces.
If this does not work, a groove of about 2 millimeters deep is made around the stone into the opal seam with a diamond saw blade.
The stone is then split open.
It results in 2 opal instead of one, almost identical, fitting together.
Depending on the size of the original opal, a pair of earrings, or a full set of earrings, pendant and a ring can be obtained with matching opal colours.
Queensland Boulder opal matrix stone can also be split into 2 pieces by knapping ( require some expertise)