Boulder Opal comes from multiple places in Australia. At one point much of Australia was a sea. It eventually dried up and formed rock and silica rich water infiltrated the stone and formed opal in the pockets.
The cabochon measures 31 x 22 x 5.5 mm. It has a girdle height approx. 2.8 mm and is sloped at 5 degrees for ease in setting. The back is also polished.
