Jewelry Blog

>Types of Australian Solid Opal
Australian opal is classified into five main types: black opal, light opal, crystal opal, boulder opal and common opal.

Black opal is opal with gem colour on a natural dark base. The dark base colour shows up the gem colours more brilliantly than in any other kind of opal. When the base colour is dark 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 in New South Wales.

Light opal contains gem colours sparkling from a white or pale-coloured body. Light opal is mined mainly at Coober Pedy, Mintabie and Andamooka in South Australia and at White Cliffs in New South Wales; some light opal is found at Lightning Ridge.

Crystal opal contains gem colours in a transparent or semi-transparent body. Crystal opal can be extremely beautiful, and is often used to make opal doublets or inlay jewellery. It is mined mainly at Andamooka in South Australia and at Lightning Ridge in New South Wales.

Boulder opal is gem-coloured opal found within a body of ironstone or iron-laden sandstone. It is named for the boulder-shaped lumps of ironstone in which it is often found. The dark-coloured stone gives some boulder opal a brilliance similar to that seen in black opal – but the gem colour usually occurs in thin, wavy sheets, so boulder opal is often cut with rock matrix showing in the face.

Common opal is opal that does not contain gem colours. Common opal has the same chemical composition as gem opal; but whereas gem opal contains microscopic spheres arranged in a regular array, in common opal the arrangement of spheres is irregular. The best-known kind of common opal is potch, which may be black, grey, white or amber-coloured. A natural backing or body of black potch is a defining characteristic of black opal (see ‘Black opal’ above).

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