Synthetic opal: how to spot it, and its value

Opal knowledge · Authenticity & synthesis

Grown, not formed

Synthetic opal is made of the same silica spheres as natural opal, but grows in about a year in the laboratory instead of over millions of years in rock. That makes it the most interesting and at the same time the most delicate stone in the opal trade: chemically genuine, optically startling, in value worlds apart. How a synthesis is made, how you recognise it for sure under the loupe, what it costs and when a grown stone is perfectly fine, we clarify step by step.

What is a synthetic opal?

A synthetic opal is a stone grown in the laboratory that matches natural opal in composition and inner structure: tiny spheres of silica, stacked densely and regularly, with a little water between them. Because those spheres diffract light, the synthesis too shows a genuine play of colour. How that diffraction works physically is explained in our article on the play of colour of opal.

The difference is not in the material, but in the origin. Natural opal grows over millions of years in cavities in rock; a synthesis forms in months in a tank. That is why gemmology classifies it as “synthetic”, not as “imitation”. An imitation only copies the look: opalite, for example, is coloured glass without a sphere structure and without genuine play of colour. And doublets and triplets are something else again: genuine natural opal in a thin layer on a backing.

Three terms, three worlds. So that you never again mix up grown and formed, the most important differences at a glance:

How is synthetic opal made?

Synthetic opal is grown by sedimentation: silica spheres of exactly the same size sink in a liquid so slowly that they order themselves into a dense, regular stack. The process copies what nature does in the cavities of old rock, only under control and in time-lapse. The natural process is described in the article How do opals form?.

From that construction follows the most important recognition feature. Because the spheres sink vertically in the tank, the ordered zones grow as narrow columns from the bottom up. In side view you later see exactly those columns, and their end faces form on the surface the scaly pattern that gemmologists call “lizard skin”. In nature, by contrast, the spheres fill irregular cavities, are disturbed, relocated and re-layered; there, zones form in all directions and never a forest of columns.

How long has synthetic opal existed?

Synthetic opal has been on the market since 1974, then introduced by the French chemist Pierre Gilson. Gilson opal is still the name that appears most often in listings, even though the process long ago changed hands and most synthetics now come from Japan and China.

How do you recognise synthetic opal?

You recognise synthetic opal most reliably under a ten-times loupe, and by three things: the lizard-skin structure inside the colour fields, the too-even size of those fields, and vertical columns in side view. With the naked eye, what stands out above all is the perfection: too much colour, too evenly distributed, in a size that as natural opal would cost a fortune.

You need no more than a loupe, good light and steady hands for the following check. Go through the five points in order:

1. Compare the colour fields

   At ten times magnification, look at the distribution of colour. Nature scatters: large and tiny patches side by side, soft edges. Synthesis sorts: fields of similar size, sharply bounded, often like mosaic tiles or a wire mesh.

2. Look into the field

   Focus on a single colour field. If it shows a fine, scaly pattern inside, as if you had lizard skin in front of you, it is with high probability a synthesis. Natural opal is smooth inside a colour patch.

3. Check from the side

   Tilt the stone into profile. In synthetics the colour zones run as vertical columns through the stone, like stalks in a bundle. In natural opal the zones lie at an angle, wavy or in layers, never as a forest of columns.

4. Weight and feel

   Resin-impregnated synthetics are noticeably lighter than a natural opal of the same size and, when rubbed with a fingernail, feel more like plastic. Under UV light they often react differently from natural opal; take that as a hint, not as proof.

5. Set price against size

   A large, flawless stone, loud red in every corner, the price of a dinner? Nature does not produce that. If size, colour and price do not fit together, it is not a lucky find, but a hint of laboratory or glass.

With synthetics the loupe is the most important checker. All further tests with which you also sort out glass, plastic and layered stones are in the guide Spotting a real opal. On a set piece of jewellery often only the view from above remains; then the lizard skin decides, and in doubt a gemmological laboratory.

What is synthetic opal worth?

A synthetic opal is worth exactly as much as its making and its cut cost, no more. Against a natural opal with comparable play of colour, body tone and size, the price sits roughly at one twentieth to one fiftieth, as of 2026 and to be read as a range, depending on the quality of the synthesis and the rarity of the natural opal. A synthesis has practically no resale value, because any number of identical stones can be produced again at any time.

For a natural opal the price is made up of body tone, brightness, pattern, colour, size and origin, and those factors are exactly what the synthesis lacks as carriers of value: its body tone is a recipe, its pattern a series product. How you assess the value of a natural stone is shown in the article How much is an opal worth?.

Does synthetic opal have to be labelled?

Yes. A synthetic opal must be named as such in the trade, and everywhere you buy it: in the title, in the description, on the invoice. The industry rules of the international jewellery associations require the word “synthetic” directly with the stone name, and competition law forbids deceiving about so essential a property. Usual formulations are “synthetic opal”, “opal, synthetic”, “lab-created opal” or “grown in the laboratory”. A bare “opal” or a fantasy name is not enough.

When is a synthetic opal fine?

A synthetic opal is always fine when you know what you are buying and the price reflects that. For fashion jewellery you wear for sport, for craft projects, dials or guitar inlays, the synthesis can even be the more sensible choice: even colour, no worry about a unique, robust in the cut.

Everything that makes an opal beyond the look, it cannot give you: the history of millions of years, the rarity, the feeling that this one stone does not exist twice, and a value that remains. Anyone giving an opal for an engagement, an anniversary or as an heirloom is looking for exactly that. That is why you find with us exclusively natural opal, every piece with a GSB certificate and five years of guarantee.

Frequently asked questions about synthetic opal

If you are unsure or have questions, you are welcome to contact us at any time, even if you did not buy the opal from us. Contact form, email cs@libertyangels.de or call +49 171 1603048.