Colour is the first thing anyone notices about a stone and the worst thing to identify it by. Ruby, spinel, garnet, tourmaline and glass can all be the same red; diamond, moissanite, cubic zirconia and white sapphire can all be the same white. What separates them is how they handle light, what’s trapped inside them, how they’ve worn, and how they’re made — and a surprising amount of that is visible with a 10× loupe and a bright window, without scratching or heating anything.
Start with the colour, then narrow it down
Pick the colour closest to your stone. The list shows the stones it’s most likely to be in a ring, their hardness on the Mohs scale, and the single observation that best tells each one apart.
- Ruby 9 Fine “silk” needles and colour zoning; almost always heat-treated.
- Lab-grown ruby 9 Flawless and vivid; curved growth lines under a loupe. Very common in old rings.
- Garnet 6.5–7.5 Darker, often brownish or wine red; no doubling. Classic in Victorian rings.
- Spinel 8 Bright, clean red; no doubling. Long mistaken for ruby, even in crown jewels.
- Rubellite tourmaline 7–7.5 Pinkish red; back facets look doubled through the top.
- Glass 5.5 Round bubbles, swirls, worn and rounded facet edges.
- Sapphire 9 Silk and straight, angular colour bands; crisp facets even after decades.
- Lab-grown sapphire or spinel 8–9 Perfectly clean and even; curved lines or tiny gas bubbles. Typical of class rings.
- Tanzanite 6–6.5 Violet-blue that shifts to purple as you turn it; facet edges wear.
- Blue topaz 8 Very clean, bright sky to steely blue; usually irradiated and heated.
- Aquamarine 7.5–8 Pale, sea-water blue; often long rectangular step cuts.
- Glass 5.5 Bubbles and swirls; often foil-backed in costume pieces.
- Emerald 7.5–8 Visible inclusions — the “jardin”; almost always oiled; edges chip.
- Peridot 6.5–7 Olive to lime green; strong doubling of the back facets.
- Tsavorite garnet 7–7.5 Vivid, clean, bright green; no doubling.
- Green tourmaline 7–7.5 Darker from the ends of the crystal; doubling.
- Doublet — A join line around the girdle; colour sits in a glue layer.
- Glass 5.5 Too clean for an emerald of that size; bubbles; rounded edges.
- Amethyst 7 Uneven colour, often deeper in bands or patches.
- Tanzanite 6–6.5 Turns from blue to violet as you rotate it.
- Purple sapphire 9 Silk and crisp facet edges; colour more even than amethyst.
- Spinel 8 Clean and bright; no doubling.
- Glass 5.5 Bubbles, swirls and scuffed facet junctions.
- Citrine 7 Often heated amethyst — a reddish-orange tint is the giveaway.
- Yellow sapphire 9 Silk, crisp edges, bright even colour.
- Topaz 8 Golden to sherry orange; slippery, glassy feel.
- Yellow diamond 10 Adamantine sparkle and fire; usually certified if valuable.
- Glass 5.5 Bubbles and swirls; costume settings.
- Diamond 10 Crisp facets, no doubling, grey-and-white sparkle with some colour.
- Moissanite 9.25 Strong rainbow fire; doubled facet edges seen through the side.
- Cubic zirconia 8–8.5 Flawless, heavy for its size, facet edges wear with time.
- White sapphire 9 Less fire than diamond; a slightly “glassy” look.
- Zircon 6–7.5 Strong doubling and worn facet edges. Natural — not cubic zirconia.
- Glass or quartz 5.5–7 Dull, rounded edges; little sparkle.
- Onyx 6.5–7 Opaque, glossy, flat-polished — the classic men’s signet stone.
- Black diamond 10 Metallic lustre, sharp facets; usually treated colour.
- Hematite 5.5–6.5 Silvery, mirror-like and heavy.
- Jet 2.5–4 Feather-light and warm to the touch. Victorian mourning jewelry.
- Black spinel 8 Faceted, bright, sharp edges.
Mohs hardness is a ranking, not a test to perform: it tells you how well a stone resists scratches, which is why soft stones show worn facet edges after years on a hand.
Six things you can check without harming the stone
1. Look for doubling
Look down through the top of the stone at the facet edges on the far side. Many gems split light into two rays — the effect is called double refraction — and in strongly doubling stones those back edges look fuzzy or doubled, like a slightly out-of-register print. Peridot, zircon, tourmaline and moissanite show it clearly; diamond, garnet, spinel, cubic zirconia and glass never do. Tilt the stone: in moissanite the effect is easiest to see looking through the side rather than straight down.
2. Look inside
Inclusions are a stone’s birth certificate. Natural gems carry crystals, feathery fractures, and in rubies and sapphires fine needles called silk, with colour arranged in straight, angular bands. Rubies and sapphires grown by the flame-fusion method — commercial since 1902, and very common in rings from the 1920s to the 1960s — show curved growth lines and occasional round gas bubbles. Glass shows round bubbles and flowing swirls. A big stone with nothing inside at all is more often lab-made or glass than a miracle.
3. Read the facet edges
You should never scratch a stone to test it, but daily wear has already done the test for you. Hard stones — diamond, sapphire, ruby — keep sharp facet junctions for generations. Softer ones — glass, tanzanite, zircon, opal, peridot, and even cubic zirconia over time — show rounded, nicked or “paper-worn” edges, most of all on the top of the stone and the corners that stick out.
4. Turn it in the light
Some stones change colour depending on the direction you look through them. Tanzanite flips between blue and violet; iolite between violet-blue and an almost colourless grey. Glass, garnet and spinel look the same from every angle. Watch the sparkle too: diamond throws white and grey flashes with some colour, moissanite throws obvious rainbows, and glass mostly just shines.
5. Check the side for a seam
A doublet is two pieces glued or fused together — often a thin slice of real garnet on top of coloured glass, a common trick in older jewelry, or two pieces of colourless material with green cement between them to fake emerald. Look at the girdle, the stone’s widest edge, from the side: a join line, a layer of different lustre or a red rim that doesn’t match the body colour gives it away. Closed-back settings make this harder, which is one reason they were used.
6. Diamonds: use the right tester
Thermal diamond testers read how fast a stone conducts heat. Diamond conducts it extremely well — but so does moissanite, which is why a thermal-only pen will call moissanite a diamond. A combined thermal-and-electrical tester separates them. Our full guide to telling a real diamond and moissanite versus diamond covers the home tests that work and the ones that don’t.
Want a quick read first? Ring Identifier looks at the whole ring — setting, metal colour and the stones together — and gives a likely description with a ballpark value, while Diamond Identifier focuses on a diamond’s cut and colour. Use them to decide which stone is worth sending to a gemmologist; a photo can’t separate natural from lab-grown.
What only a lab can tell you
Some questions don’t have a home answer. Natural or lab-grown is the big one: chemically and physically the stones are the same, and telling them apart needs spectroscopy and specialist microscopes. Treatments — heating, oiling, filling, irradiation, coating — are the other. Most sapphires and rubies are heated and most emeralds are oiled, which is accepted when it’s disclosed and changes the price when it isn’t. If a stone might be valuable, a report from an independent laboratory such as GIA settles species, origin of growth and treatment in one document.
- Don’t
- Scratch, heat or acid-test a stone
- Doubling
- Peridot, zircon, tourmaline, moissanite — not diamond, garnet, spinel, CZ
- Curved growth lines
- Flame-fusion lab ruby or sapphire
- Round bubbles, swirls
- Glass
- Worn facet edges
- A softer stone — not diamond, sapphire or ruby
- Needs a lab
- Natural vs lab-grown, and treatments
The takeaway
Narrow the colour to a shortlist, then let the loupe do the work: doubling, inclusions, facet wear, colour shift and the side view eliminate most candidates without harming anything. What’s left is usually two or three possibilities, and a jeweler with a refractometer — or a lab, for a stone that matters — can finish the job. To place the ring around the stone in time, see how to date a vintage ring; to read the metal, how to identify a ring.
At a glance
| Observation | Points to |
|---|---|
| Doubled back facets | Peridot, zircon, tourmaline, moissanite |
| No doubling | Diamond, garnet, spinel, cubic zirconia, glass |
| Curved growth lines | Flame-fusion lab ruby or sapphire |
| Silk and straight colour bands | Natural ruby or sapphire |
| Round bubbles, swirls | Glass |
| Join line at the girdle | Doublet or triplet |
| Colour shifts as you turn it | Tanzanite, iolite |
Frequently asked questions
How can I tell a ruby from a garnet?
Rubies are usually brighter, purer red with fine silk inclusions and very sharp facet edges; garnets tend toward darker wine or brownish red. A gemmologist’s refractometer separates them in seconds.
Is my sapphire real or glass?
Look for round bubbles and swirls (glass) versus silk and straight colour banding (natural sapphire). Glass also shows worn, rounded facet edges; sapphire stays sharp.
Can I tell if a gemstone is lab-grown at home?
Sometimes: flame-fusion rubies and sapphires show curved growth lines. Modern lab-grown stones can be inclusion-free and identical in properties, and need a gem lab.
Should I do a scratch test?
No. Scratching damages the stone and the result is unreliable. Read the wear the stone already has instead.
Sources and further reading
- Gem Encyclopedia — GIA
- Mohs scale — Wikipedia
- Birefringence — Wikipedia
- Verneuil method — Wikipedia
- Doublet (lapidary) — Wikipedia
- Moissanite — Wikipedia
Links checked October 4, 2026.
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