How to Tell a Genuine Stone from a Fake: A Practical Guide

You can recognise a genuine natural stone because it feels cool and warms slowly in your hand, reveals tiny inclusions rather than perfect clarity under a magnifying glass, and has a hardness consistent with the Mohs scale for that mineral. No single test provides certainty, so in this guide we combine several methods - from simple tests you can perform at home to questions worth asking the seller. You will also find specific tips for turquoise, tiger’s eye, emerald, topaz and amethyst.

Why are natural stones counterfeited?

Natural stones such as amethyst, amber and jadeite have commanded high prices for years - and that is precisely why the counterfeit market is thriving. The most common imitations are coloured glass, plastics and cheaper minerals dyed to resemble more expensive ones (a classic example: howlite dyed to look like turquoise). Reconstructed stones are also found; these are compressed mineral powder combined with resin.

Synthetics must be distinguished from imitations. A synthetic stone is created in a laboratory, but has the same chemical composition and structure as a natural one - so it is not “fake”; it simply does not come from the earth. An honest seller always states this in the description - including when their range contains materials that are not minerals. We do the same: in Brazi stone jewellery, the vast majority consists of natural stones, but you will also find opalite, or opalescent glass - and we say so openly, because confusing it with opal is one of the more common misunderstandings on the market.

How to identify a genuine stone? Five characteristics you can check right away

The same principles make it possible to identify natural stones of almost any kind. Before moving on to tests for specific minerals, assess five basic characteristics:

• Appearance and inclusions: genuine natural stones have unique inclusions, streaks and minor imperfections that are difficult to imitate. An imitation often looks “too perfect” - without inclusions, with a glassy, uniform surface.
• Touch and temperature: a mineral feels distinctly cool when first touched and slowly absorbs the warmth of your hand. Plastic becomes warm almost immediately, while glass heats up faster than stone.
• Weight: a natural stone is noticeably heavier than a plastic imitation. Note: glass has a density similar to quartz, so weight alone is not enough - combine it with other tests.
• Colour: natural colour is usually varied, with zoning and lighter and darker areas. A uniform, overly saturated colour, as well as dye collecting in cracks and hollows, are warning signs.
• Price and description: a gemstone-quality mineral has a market value. If an “emerald” costs as much as a cup of coffee and the description does not even state the mineral’s name, it is almost certainly an imitation.

Be careful with chemical tests. Some carbonate minerals (e.g., malachite) react with acids, but this is a destructive test - leave it to gemologists and never perform it on jewelry.

The Mohs scale, or a practical hardness test

Hardness is one of the most difficult mineral properties to counterfeit. The Mohs scale ranks minerals from 1 (talc) to 10 (diamond): each stone scratches materials softer than itself and remains resistant to them. In practice, everyday objects are enough: a fingernail has a hardness of about 2.5, a copper coin about 3, a knife blade and glass about 5.5, and a steel file about 6.5.

Stone	Mohs hardness scale	Practical tip
Amber	2–2,5	Very soft - even a copper coin can scratch it; it is also warm and light
Malachite	3,5–4	Easy to scratch with a knife; requires gentle handling
Obsidian	5–5,5	Natural volcanic glass with hardness similar to that of a knife blade
Turquoise	5–6	A knife may scratch it - its hardness is similar to that of glass
Onyx	6,5–7	A variety of chalcedony; a knife will not leave a mark on it
Amethyst, citrine, tiger's eye, rock crystal (quartz varieties)	7	They scratch glass, and a knife will not scratch them
Emerald	7,5–8	Harder than quartz; inclusions are normal in it, not a flaw
Topaz	8	Scratches quartz; a glass imitation will fail this test
Diamond	10	The hardest mineral - no other stone can scratch it

One caveat: the scratch test is invasive. Perform it only in an inconspicuous place on the stone, and preferably not at all on finished jewelry, to avoid damaging the polish or setting.

At-home tests step by step

How can you check whether a stone is genuine without a laboratory? In this order - from the simplest to the most demanding test:

1. Jeweler's loupe (10x magnification): a gemologist's basic tool. Look for natural inclusions and color zoning; round air bubbles are an almost certain sign of glass.
2. Temperature test: place the stone against the inside of your wrist. A mineral will feel cool and warm up slowly; plastic feels warm immediately.
3. Weight test: compare the stone with a similar-sized imitation. Plastics are noticeably lighter than minerals.
4. Hardness test: according to the table above - for example, quartz (amethyst, tiger's eye) will scratch glass, while topaz will scratch quartz.
5. Light: examine the stone in strong light from different angles. Natural minerals refract light unevenly; perfect clarity combined with a “dead” luster indicates an imitation.
6. Thermal conductivity tester: for diamonds, authenticity is determined by thermal conductivity, tested with a jeweler's tester - have this test performed by a professional.

How can you tell if a particular stone is genuine?

General tests are only the beginning - every mineral has its own distinctive features and typical imitations. Here are the stones you ask about most often.

How can you tell if turquoise is genuine?

The most common imitation of turquoise is dyed howlite or magnesite - a light-colored mineral with gray veins that, once dyed, deceptively resembles the original. Genuine turquoise has a hardness of 5-6, a waxy luster, and a price commensurate with its rarity - natural, gem-quality turquoise is never cheap. To identify genuine turquoise, rub it in an inconspicuous spot with a cotton swab soaked in acetone: if the swab picks up the color, you are dealing with a dyed imitation. Also ask whether it has been stabilized with resin - this is a common and accepted treatment, but a reputable seller should disclose it.

How can you tell if tiger's eye is genuine?

The distinguishing feature of tiger's eye is the cat's-eye effect: a silky band of light that moves across the surface as you rotate the stone. This is due to the mineral's fibrous structure - a glass or plastic imitation has a static pattern that looks printed on. Tiger's eye is a variety of quartz with a hardness of 7, so it scratches glass and feels distinctly cool when first touched.

How can you tell if an emerald is genuine?

Natural emeralds almost always have visible inclusions - gemologists call them “jardin,” meaning garden. An ideally clear, intensely green stone at a low price is most likely glass or synthetic; green glass also reveals itself through round air bubbles visible under a loupe. Emerald has a hardness of 7.5-8, so neither a knife nor glass will scratch it. For more expensive specimens, always ask for a certificate from a gemological laboratory.

How can you tell if topaz is genuine?

Topaz has a hardness of 8 - it will scratch quartz and glass while remaining unmarked itself. It feels very smooth to the touch, almost “slippery,” cold, and warms more slowly than glass imitations. A physical curiosity: when rubbed against wool, it becomes electrically charged and attracts small scraps of paper. Most blue topaz on the market gets its color through irradiation and heating - it is still a natural stone, but this information should be included in the description.

How can I identify genuine amethyst?

Hold the stone up to the light: natural amethyst is almost never perfectly uniform in color. Zoning - lighter and darker purple streaks - is characteristic, as are small inclusions within the mineral. A perfectly clear, intensely purple stone at a suspiciously low price is usually synthetic. As a variety of quartz, amethyst has a hardness of 7 and scratches glass.

How can I tell if rock crystal is genuine?

Rock crystal is most often imitated with ordinary glass, but the differences are easy to spot: natural quartz is harder (7 compared with approximately 5.5), feels cooler to the touch, and often contains subtle cloudiness or “veils.” Glass is warmer, softer, and full of round air bubbles. We have collected detailed tests in a separate guide: how to check whether rock crystal is genuine.

Certificate, stone description, and safe shopping

If you're looking for certified natural stone bracelets, keep your expectations realistic: full gemological certificates are issued mainly for expensive gemstones such as emeralds, sapphires, and diamonds. For jewelry made from popular minerals, a reliable statement from the seller is the market standard.

That's why the most important “certificate” is a good description. A reliable description of a natural stone should state the mineral name, information about any treatment (dyeing, stabilization, heating), and ideally its origin as well. Always ask the seller about these three things - avoiding an answer says more than many a label. Apply the same principles to every type of jewelry, from bracelets to natural stone necklaces.

Summary: a quick authenticity checklist

Here's how to check within a few minutes whether stones are genuine:

• a cool feel and slow warming in your hand,
• natural inclusions and color zoning instead of perfect clarity,
• a noticeably greater weight than plastic,
• hardness consistent with the Mohs scale (quartz scratches glass, topaz scratches quartz),
• no round air bubbles visible under a magnifying glass,
• a fair price and a description with the mineral name and information about treatment.

One positive result is not enough - certainty comes only from several consistent tests. And when buying finished jewelry, choose sellers who clearly state what their stones are made of.