Real vs fake gemstones

Why fakes exist

Gemstones are sold by color, clarity, and name, and each of those can be faked. Glass imitations are cheap, widely produced, and often convincing at a glance. Plastic resins mimic amber. Dyed quartz stands in for higher-priced colored stones.

Lab-grown gems are not fakes (they are correctly classified, disclosed gems), but undisclosed lab-grown material sold as natural is a form of fraud. Treated stones (heat, irradiation, fracture-filling, oil) are real gems but should be disclosed; non-disclosure is the issue.

12 tests for spotting a fake at home

1. Visual inspection under bright natural light. Look for bubbles (glass), seams (molded plastic), color concentrations at cut edges (dyed), and unnatural uniformity. Most real gems have subtle inclusions.
2. Test with a loupe. A 10x jeweler's loupe reveals surface scratches, bubble trails, and swirl marks from molded glass. Real gemstones typically show crystal growth features, not flow patterns.
3. Check the heft. Real gems are typically denser than glass or plastic. A suspiciously light “ruby” or “sapphire” is often glass. Compare against a known piece when possible.
4. Temperature test. Glass and plastic warm quickly against the cheek; most gemstones stay cool longer. This is suggestive, not definitive.
5. Scratch test on a known surface. Real corundum (sapphire, ruby) at Mohs 9 will scratch a steel file or glass. Glass imitations will not scratch steel. Test on an inconspicuous area only.
6. Water displacement density check. Measure the stone's weight (grams), then its water displacement volume (mL). Density = weight / volume. Compare against published density (specific gravity) for the claimed gem species. Ruby: 4.0. Glass: 2.4 to 2.8.
7. UV fluorescence. Many natural gems fluoresce specific colors under shortwave and longwave UV. Ruby typically shows strong red fluorescence. Amber fluoresces pale blue. Dyed imitations often show no or wrong-color fluorescence.
8. Flashlight in dark room. Looking through a clear gem under backlight reveals color zoning, internal bubbles, or inclusion patterns that indicate natural origin or specific type.
9. Breath test on opal. Genuine opal does not fog with breath in the same way glass does. This is subtle and requires practice.
10. Needle-through-amber. Real amber (fossilized resin) will give off a pine-resin smell when a hot needle is touched to an inconspicuous spot. Plastic or copal smells like burning plastic. Use on back of bead only; this is a last-resort test.
11. Magnet test on hematite. Real hematite is only weakly paramagnetic. Most “magnetic hematite” jewelry is actually synthetic ceramic called hematine, which is strongly magnetic. This is a fake if labeled as real hematite.
12. Certificate check. For any stone over approximately $200, demand a grading report from an independent gemological laboratory. The cost of the report is a small fraction of the stone and protects your purchase.

Common fakes you will encounter

• Red glass sold as ruby (frequent at tourist markets worldwide)
• Blue glass sold as sapphire
• Howlite dyed blue and sold as turquoise
• Plastic copal sold as amber
• Dyed chalcedony sold as black onyx (legal when disclosed; fraud when not)
• Synthetic moissanite sold as diamond (undisclosed)
• Magnetic hematine sold as hematite
• Lead glass-filled corundum (“composite ruby”) sold as natural ruby at inflated prices
• Reconstituted turquoise (ground turquoise powder with resin binder) sold as solid turquoise

When to get professional testing

Labs that provide grading reports

• Gemological Institute of America (GIA) – US, global
• American Gemological Laboratories (AGL) – US
• Gübelin Gem Lab – Switzerland
• Swiss Gemmological Institute (SSEF) – Switzerland
• American Gem Society (AGS) – US

What a gemologist can tell you that you cannot

A certified gemologist uses a refractometer (measures refractive index to 0.001), a polariscope (tests for single vs double refraction and anomalous optical behavior), a microscope for inclusion analysis, UV-visible and FTIR spectroscopy, and sometimes Raman spectroscopy. These tools can distinguish natural ruby from flux-grown synthetic in ways no home test can.

Buying smarter

1. Buy from sellers with published return policies. If you can return the stone within 30 days for any reason, you can send it for independent testing.
2. Ask about treatment at the point of sale, in writing. Reputable sellers disclose heat, irradiation, and filling routinely.
3. Learn the price range for the stone you want. A “top-grade ruby” at $100 per carat is nearly certainly misrepresented.
4. Verify the lab report. An independent gemological lab reports have QR codes and scan into their online verification system. If a seller offers a lab report, scan it.
5. Trust mineral specimen shows and established jewelers over street vendors and auction-site sellers without history.

Frequently asked questions