Why This Matters
The opal market includes a wide spectrum of stones — from rare natural gems worth thousands of dollars per carat to synthetic laboratory-created opals that cost just a few dollars. Both can display dazzling play-of-color, which makes visual identification tricky. Knowing how to tell them apart protects you as a buyer and helps you understand what you already own.
What Are Synthetic Opals?
Synthetic (lab-created) opals have the same chemical composition as natural opals — they are silicon dioxide with water — but they are grown in a laboratory rather than formed over millions of years in the earth. Common brands include Gilson opals. There are also opal simulants, such as glass or plastic imitations, which don't even share the same chemistry.
Visual Clues: What to Look For
The "Snakeskin" or "Lizard Skin" Pattern
One of the most reliable visual giveaways of a synthetic opal is an unnaturally regular, geometric pattern in the play-of-color — sometimes described as a "snakeskin" or "lizard skin" pattern. Natural opals have organic, irregular color patterns. If the colors look too perfectly tiled or repetitive, be suspicious.
Color Under Different Lighting
View the stone under various light sources — daylight, incandescent, and fluorescent. Natural opals can behave quite differently across light types. Synthetic opals often display color that appears slightly flat or uniformly bright regardless of the angle or light source.
Transparency and Body
Many synthetic opals have a milky, plastic-like transparency that differs from the more complex translucency of natural crystal opals. Hold the stone up to a light source and look through it — a natural stone will often show depth and variation.
Physical and Practical Tests
Temperature
Natural gemstones feel cool to the touch, while plastic simulants warm up quickly in your hand. This won't distinguish a natural opal from a synthetic one (both are mineral), but it will help identify plastic fakes.
Magnification
Using a loupe (10x magnification) or a gemologist's microscope can reveal the internal structure. Synthetic opals often show a very regular, columnar or hexagonal microstructure, while natural opals display more chaotic, irregular patterns.
Weight (Specific Gravity)
Natural precious opal has a specific gravity of approximately 2.15. Plastic simulants are significantly lighter. If you have access to a precise scale and can perform a water displacement test, this can be a useful indicator.
Comparison Table
| Feature | Natural Opal | Synthetic Opal | Plastic Simulant |
|---|---|---|---|
| Color Pattern | Organic, irregular | Regular, geometric | Uniform or printed |
| Temperature | Cool to touch | Cool to touch | Warms quickly |
| Magnified structure | Chaotic/varied | Regular columns/hexagons | No structure |
| Value | High | Low | Very low |
When in Doubt, Get a Professional Opinion
If you're considering a significant purchase or have a stone whose identity you're unsure of, consult a certified gemologist or send the stone to a reputable gem-testing laboratory. Organizations such as the Gemological Institute of America (GIA) and the Australian Gemmological Laboratory (AGL) can issue certificates confirming a stone's natural origin. This certificate also adds resale value to your stone.
The Bottom Line
Synthetic opals aren't inherently bad — they're beautiful, affordable, and perfectly valid for jewelry. The problem arises when they're sold as natural stones at natural prices. Arm yourself with these identification skills, and don't hesitate to ask for provenance documentation on any significant purchase.