Why Fake Gemstones Are a Real Problem
The gemstone market ranges from small street vendors to high-end auction houses — and at every level, synthetic, treated, or outright fake stones make their way to unsuspecting buyers. Understanding how to identify and avoid these stones can save you significant money and disappointment.
It's important to distinguish between three categories of "non-genuine" stones:
- Simulants – Stones that look like a gem but have a completely different composition (e.g., glass sold as sapphire)
- Synthetics – Lab-grown stones with the same chemical composition as natural gems (e.g., lab-created ruby)
- Treated naturals – Real gems that have been heated, oiled, irradiated, or filled to improve appearance
Synthetics and treated stones are not inherently dishonest — but they must be disclosed. The problem arises when they're sold as untreated, natural stones at natural-stone prices.
Simple At-Home Tests
The Breath Test (Fogging)
Breathe on the stone as you would on glass. Natural gemstones like sapphire, ruby, and diamond dissipate heat quickly — fog clears in 1–2 seconds. Glass retains warmth longer and stays foggy for several seconds. This is a rough indicator only, not definitive proof.
The Weight Test
Genuine gemstones have specific gravities quite different from glass. Topaz, for example, is noticeably heavier than glass of the same size. If a "gemstone" feels unusually light, be suspicious.
Scratch Testing
Using the Mohs hardness scale as a guide:
- A genuine diamond (Mohs 10) will scratch everything
- Topaz (Mohs 8) will scratch quartz (Mohs 7) but not corundum
- Glass (Mohs ~5.5) is easily scratched by most genuine gems
Be careful: scratch tests can damage both the test stone and the gem. Use this method only on inconspicuous areas of loose stones.
Bubble Inclusions
Look through a loupe or magnifying glass. Rounded, bubble-like inclusions are a hallmark of glass imitations. Natural gemstones contain inclusions too, but they are typically irregular — crystals, needles, fingerprints, and fractures — not perfect bubbles.
Red Flags When Shopping
- Prices that seem too good to be true — A "natural ruby" selling for the same price as a semi-precious stone is almost certainly treated, synthetic, or fake.
- No paperwork or certification — Reputable sellers of valuable stones provide laboratory certificates (GIA, AGL, Gübelin, GRS).
- Vague descriptions — Terms like "ruby-colored," "sapphire-style," or "topaz glass" are red flags for imitations.
- Perfect clarity in emeralds — Nearly all natural emeralds have visible inclusions. An eye-clean emerald at a low price should be questioned.
- Pressure to buy quickly — Legitimate gem dealers welcome scrutiny and questions.
Professional Tools That Help
| Tool | What It Detects | Accessibility |
|---|---|---|
| 10x Loupe | Inclusions, bubbles, surface wear | Affordable, widely available |
| Refractometer | Refractive index (identifies mineral type) | Mid-range, requires practice |
| Spectroscope | Absorption spectrum (detects treatments) | Intermediate cost |
| UV Lamp | Fluorescence patterns (reveals some synthetics) | Affordable |
| Lab Certificate | Full gem identification and treatment disclosure | Paid service (GIA, AGL, etc.) |
The Bottom Line
No single at-home test is conclusive. For any purchase over a few hundred dollars, always request a laboratory certificate from a recognized gemological institution. The cost of a lab report is a small fraction of a gem's value and provides real peace of mind. When in doubt, consult a certified gemologist before committing to a purchase.