Opal Gemstone Identification
The majority of opal stone (almost 95%) comes from Australia. Mexico, Brazil, Ethiopia, and the USA are some of the other places from where it comes. This gem comprises tiny spheres of silica. It is formed when silica-rich water seeps into the Earth’s crust. From there, it is separated into two categories: common and noble opal.
Physical properties/chemical composition
The chemical composition of opal stone is SiO2 nH2O+aI, Fe, Ca, Mg, and Na in traces. Some contain small amounts of radioactive elements. Water percentage is a variable. Its hardness is 5.5–6.5 on the Mohs scale. The specific gravity (S.G.) ranges between 1.98 and 2.20, and the refractive index (R.I.) lies between 1.40 to 1.47.
Synthetic opal, Gilson created opal, Slocum glass, opalite (a plastic imitation with the play of color), composite (doublets and triplets), mother of pearl (some of it costly), and chalcedony.
Identification / How to check
Here are some tests for opal gemstone identification that you can do easily.
1. Origin Test
A major chunk of this comes from Australia (almost 95%). Therefore, check the country of origin or confirm it with the certification provider, dealer of stone, or shop owner from whom you are buying. This is because Russian and Hong Kong-produced fake give the appearance of being real.
2. Irregularities Test
Since it is a natural stone, it will retain some asymmetry in its shape even after cutting. This implies that if your opal stone is perfectly circular or oval, then you should consider inspecting it properly before buying it or buying it from a certified and authentic dealer.
3. White light test
Place the stone on a table and pass the white light over it. If it shows different layers of color, it is a sign of real and good quality. Be cautious when looking at color layers; if it appears just below the surface, it could be a fake.
Note: Do not use fluorescent lighting, as it may appear more fired than it is.
4. Look for pricing
Real opal stones are a little bit more costly. If you are getting this at an extremely lower price than usual, you need to doubt the fakeness of the stone. However, you should also consider checking the quality.
5. Observe patterns closely
Take your stone to the laboratory and carefully observe the large patches of color. If you find snaky patterns of colors that are very symmetrical and too perfect, it is possible that they are fake or synthetic, as the real ones do not have that much perfection in the rainbow effect.
Crystalline inclusions (needles), Flow structures, Cloud-like inclusions, and Dendritic inclusions.