Australian Opal

Buying this stone

Where it came from, what its weight band is for, and what to check before any money changes hands.

The deposit

Lightning Ridge in New South Wales is the only significant source of black opal on earth, and black here refers to body tone rather than to the colours in the stone: a dark body is what makes play of colour read as vividly as it does, because the colour is seen against a dark ground instead of a milky one. Australia has supplied the great majority of the world’s precious opal for over a century, and the three fields produce three different materials, with Coober Pedy yielding light and white opal and the Queensland fields yielding boulder opal on ironstone.

This stone

This is a matched pair at 7.05 carats total, and a pair is a fundamentally different proposition from two stones of the same weight. Opal cannot be cut to order the way a faceted stone can, because the play of colour sits in a thin layer and the cutter follows it rather than a template. Two opals that agree on body tone, pattern, dominant colour and the direction the colour fires in are found rather than made, and pairs are consequently scarcer than single stones of the same quality. This one is destined for earrings, which is what a pair is almost always for.

Treatment

Unheated and untreated, and for opal the more important question is a structural one that sits alongside treatment: whether the stone is solid or assembled. A doublet is a slice of opal cemented onto a dark backing and a triplet adds a clear cap over that, and both are worth far less than solid opal while looking very similar face up. These are solid. Opal is also sometimes smoked or sugar treated to darken the body tone artificially, which neither of these has had.

The report

No report is held for this 7.05 cts (Pair) opal stone yet, and we would rather say that than name a laboratory that has not seen it. We will submit it to IGI or IIGJ before purchase on request.

Before you pay

• Look at each stone from the side, not the face. An assembled stone shows a dead straight join line that a solid one cannot have.
• Tilt both together through the full range and check the colour fires in the same direction. A pair that only matches at one angle is not a pair.
• Keep opal away from heat and very dry storage. It contains water and can craze.

Read next

Heera, the diamond covers the material itself and what gets sold in its place. How to buy a coloured stone covers pricing, treatment and reports.

Written by Kamal Kishore Agarwal, founder and gemmologist, Gem-A qualified, buying in Johari Bazaar since 2008.