Black Opal is opal formed with a bar of gem coloured opal
on a natural black/dark opal base. The dark opal base shows the gem colours more brilliantly than in any other kind of opal. When the base colour is grey rather than black, the opal may be referred to as ‘semi-black’ or ‘grey’. Black opal is the most rare and valuable opal type. Nearly all of the world’s supply
of black opal is mined at Lightning Ridge.