Is Gilson opal a real opal?

In the 1970s a French ceramicist named Pierre Gilson discovered how to create or grow a number of simulated gemstones.  They are called synthetic in the trade but they aren't really as they don't share the properties of their natural counterparts, they are really simulants or imitation gemstones. These include lapis lazuli, turquoise, emerald and opal.

In the photo you can see a cube of ‘synthetic’ opal together with a cabochon of the same material. Differing to natural opal, you can very clearly see the columnar growth of the material by the stripes of colour along the side of the cube which can also be seen if you look at the side view of a cabochon from this material.

One of many different imitation opal materials found on the market, this one is described as having a ‘lizard skin’ or ‘chicken wire’ appearance. Keep a look out for this when buying your opals!