**Gemstone Identification Chart — Colour, Hardness, Effects** > Free gemstone identification key covering 27 gems and their imitations. Filter by colour, hardness, transparency and optical effect, with simulants named. Source: https://orvik.app/tools/gemstone-identifier/ · updated: 2026-09-04 1. [Orvik](https://orvik.app/) 2. [Free tools](https://orvik.app/tools/) 3. Rocks & minerals Rocks & minerals # What gemstone is this? Colour alone identifies almost nothing — ruby, red spinel, garnet and glass all look the same across a room, and for two hundred years the most famous "ruby" in the British crown jewels was a spinel. Filter by **colour plus hardness plus any optical effect**, and check the look-alike line on every entry, because for gemstones the imitation is usually the answer. Entries **27** Filters **5** Updated **2026-09-04** Cost **Free, no account** Narrow it down Clear all Search gemstones by name Colour Red or pink Blue Green Yellow, orange or brown Purple Colourless or white Black or dark Multicoloured or banded Hardness Test on an unpolished spot such as the girdle, never a facet. Under 6 — a steel file marks it 6–7 — scratches glass 7.5–8.5 — scratches quartz 9 and above Transparency Transparent Translucent Opaque Optical effect None A star A cat's eye Flashes of colour that move A floating sheen or glow Changes colour under different light Category Natural gemstone Organic Simulant or synthetic Showing all 27 gemstones 1. ### Diamond C — carbon Extreme brilliance and hard, sharply defined facet edges that stay crisp because nothing abrades them. Singly refractive, so facet edges seen through the table are single, not doubled. Size Mohs 10; refractive index 2.42 Where Kimberlite pipes in southern Africa, Russia, Canada and Australia. Confused with Moissanite doubles the facet edges under magnification. Cubic zirconia is denser and has lower thermal conductivity, which is what a jeweller's pen tester measures. The old "scratches glass" test proves nothing — all three do. In the record Mohs 10 · C · isometric · adamantine lustre [check on Macrostrat](https://macrostrat.org/) 2. ### Ruby Corundum, Al₂O₃ Red corundum, from pinkish to deep pigeon's blood, with a strong red fluorescence under ultraviolet light in Burmese material. Star rubies show a six-rayed star from oriented rutile needles. Size Mohs 9 Where Myanmar, Mozambique, Thailand, Madagascar. Confused with Red spinel, which is softer at 8 and singly refractive; garnet, which is softer still; and glass. The Black Prince's Ruby in the Imperial State Crown is a spinel. In the record Mohs 9 · Al2O3 · trigonal · adamantine lustre [check on Macrostrat](https://macrostrat.org/) 3. ### Sapphire Corundum, Al₂O₃ Corundum in any colour except red, so there are yellow, pink, green and colourless sapphires as well as blue. Very hard, with a slightly oily lustre and often visible straight colour banding. Size Mohs 9 Where Sri Lanka, Madagascar, Kashmir, Montana, Australia. Confused with Tanzanite, which is much softer at 6 to 7 and shows different colours from different directions. Blue glass and synthetic sapphire are both common; synthetic material is chemically identical and needs a lab to detect. In the record Mohs 9 · Al2O3 · trigonal · adamantine lustre [check on Macrostrat](https://macrostrat.org/) 4. ### Emerald Handle with care Beryl, Be₃Al₂Si₆O₁₈ Deep green beryl, almost always heavily included — the internal fractures and crystals are called the jardin, the garden, and their absence in a clean stone is a warning rather than a virtue. Size Mohs 7.5–8 Where Colombia, Zambia, Brazil, Afghanistan. Confused with Green glass, synthetic emerald, and doublets glued from two pieces with green cement. Most natural emerald is oil- or resin-treated to fill the fractures, which is normal and disclosed but affects durability and cleaning. Risk Never clean an emerald ultrasonically or with steam. It strips the filling and can crack the stone along an existing fracture. In the record Mohs 7.5–8 · Be3Al2(Si6O18) · hexagonal · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 5. ### Aquamarine Beryl, Be₃Al₂Si₆O₁₈ Pale sea-blue to blue-green beryl, typically very clean, in large flawless crystals. Colour is usually pale in natural stones; a deep blue aquamarine has almost always been heat-treated. Size Mohs 7.5–8 Where Brazil, Pakistan, Nigeria, Madagascar. Confused with Blue topaz, which is denser and heavier for its size, and blue glass, which contains bubbles. In the record Mohs 7.5–8 · Be3Al2(Si6O18) · hexagonal · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 6. ### Amethyst Quartz, SiO₂ Purple quartz, often with visible colour zoning in angular bands or a paler zone towards the crystal base. Sold in geodes and clusters everywhere. Size Mohs 7 Where Brazil, Uruguay, Zambia, Russia. Confused with Purple glass and synthetic amethyst, which is chemically identical and cheap. Deep colour fades in prolonged sunlight, which is real and irreversible. In the record Mohs 7 · SiO2 · trigonal · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 7. ### Citrine Quartz, SiO₂ Yellow to orange-brown quartz. Natural citrine is a pale lemon; almost every deep orange-brown "citrine" on the market is heat-treated amethyst, which is legitimate and should be disclosed. Size Mohs 7 Where Brazil, Bolivia, Madagascar. In the record Mohs 7 · SiO2 · trigonal · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 8. ### Topaz Handle with care Al₂SiO₄(F,OH)₂ Hard, bright and noticeably heavy for its size, with a slippery slightly soapy feel. Almost all blue topaz on the market is irradiated and heated colourless material. Size Mohs 8 Where Brazil, Nigeria, Pakistan, Russia. Risk Perfect basal cleavage. Topaz resists scratching beautifully and splits from a single sharp knock, so it needs a protective setting in a ring. In the record Mohs 8 · Al2(SiO4)(F,OH)2 · orthorhombic · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 9. ### Garnet X₃Y₂(SiO₄)₃ group A whole family rather than one stone. Deep red almandine is the familiar one; there are also orange spessartine, green tsavorite, brilliant green demantoid and colour-change species. Singly refractive with no cleavage. Size Mohs 6.5–7.5 Where Worldwide; almandine in schist, demantoid in Russia, tsavorite in Kenya. Confused with Ruby, which is much harder and fluoresces red. Garnet is denser than most red stones and sinks fast in heavy liquids, which is how gemmologists separate them. In the record Mohs 6.5–7.5 · X3Z2(SiO4)3 · isometric · vitreous to resinous lustre [check on Macrostrat](https://macrostrat.org/) 10. ### Peridot Olivine, (Mg,Fe)₂SiO₄ A distinctive oily olive-green with a yellow undertone, and strong double refraction — look through the table with a loupe and the back facet edges appear doubled. Size Mohs 6.5–7 Where Arizona, Pakistan, Myanmar, and in meteorites. Confused with Emerald and green glass. The doubled facet edges are diagnostic and easy to see. In the record Mohs 6.5–7 · (Mg,Fe2+)2SiO4 · orthorhombic · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 11. ### Tourmaline Complex borosilicate Comes in more colours than any other gem species, often several in one crystal — watermelon tourmaline is pink-cored and green-rimmed. Rough crystals have a rounded-triangular cross-section with heavy lengthwise striations. Size Mohs 7–7.5 Where Brazil, Afghanistan, Nigeria, Maine, California. In the record Mohs 7 · A(D3)G6(T6O18)(BO3)3X3Z · trigonal [check on Macrostrat](https://macrostrat.org/) 12. ### Spinel MgAl₂O₄ Bright, singly refractive and often in octahedral crystals. Historically sold as ruby, and now increasingly valued in its own right for the vivid red and the cobalt blue. Size Mohs 8 Where Myanmar, Tanzania, Sri Lanka, Vietnam. Confused with Ruby. Spinel is singly refractive and ruby is doubly refractive — a polariscope or a loupe check for doubled facet edges settles it in seconds. In the record Mohs 7.5–8 · MgAl2O4 · isometric · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 13. ### Tanzanite Handle with care Zoisite, Ca₂Al₃(SiO₄)₃(OH) Violet-blue with strong pleochroism — it shows blue, violet and burgundy from three different directions, which is visible by rotating the stone in the hand. Nearly all material is heat-treated to remove the brown. Size Mohs 6–7 Where One hill in Tanzania and nowhere else on Earth. Risk Soft, with distinct cleavage and sensitivity to sudden temperature change. A poor choice for an everyday ring and unsuited to ultrasonic cleaning. In the record Mohs 6–7 · {Ca2}{Al3}(Si2O7)(SiO4)O(OH) · orthorhombic · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 14. ### Opal Handle with care SiO₂·nH₂O Flashes of spectral colour that move as the stone moves — play of colour, produced by diffraction from a regular array of silica spheres. This is not the same as an overall body colour. Size Mohs 5.5–6.5 Where Australia, Ethiopia, Mexico, Brazil. Confused with Doublets and triplets, thin slices of opal backed with dark material and capped with quartz or glass. Look at the stone from the side: a straight-line junction means an assembled stone. Risk Contains up to 20% water and crazes into a network of fine cracks if dried by heat or low humidity. Never ultrasonic, never steam, never leave in a hot car. In the record Mohs 5.5–6.5 · SiO2·nH2O · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 15. ### Moonstone Orthoclase feldspar A soft blue or white glow that floats across the surface and moves as you tilt the stone — adularescence, caused by light scattering between microscopic layers of two feldspars. Size Mohs 6–6.5 Where Sri Lanka, India, Madagascar. Confused with Opalite, a manufactured glass sold widely as moonstone, which contains bubbles and has a flat orange glow in transmitted light. 16. ### Labradorite Plagioclase feldspar Dull grey until the angle is right, then a broad flash of peacock blue, green or gold across the whole surface — labradorescence, from light interference in internal lamellae. Size Mohs 6–6.5 Where Labrador, Finland, Madagascar. In the record Mohs 6–6.5 · (Ca,Na)[Al(Al,Si)Si2O8] · sub-vitreous lustre [check on Macrostrat](https://macrostrat.org/) 17. ### Turquoise CuAl₆(PO₄)₄(OH)₈·4H₂O Opaque sky-blue to green, usually with a web of dark host rock called matrix. Porous, so it absorbs oils and changes colour over years of wear. Size Mohs 5–6 Where Iran, the US Southwest, China. Confused with Dyed howlite and magnesite, which are extremely common and can be detected by rubbing an inconspicuous spot with acetone — the dye lifts. Most commercial turquoise is stabilised with resin, which is standard practice. In the record Mohs 5–6 · Cu(Al,Fe3+)6(PO4)4(OH)8·4H2O · triclinic · sub-vitreous lustre [check on Macrostrat](https://macrostrat.org/) 18. ### Lapis lazuli Lazurite in a rock matrix Deep ultramarine blue flecked with brassy specks of pyrite and often white streaks of calcite. It is a rock rather than a mineral, which is why the composition varies. Size Mohs 5–6 Where Afghanistan, principally the Sar-e-Sang mines, for over 6,000 years. Confused with Dyed jasper sold as lapis, which is uniformly blue with no pyrite. Ground lapis was the source of ultramarine pigment and was once worth more than gold. 19. ### Jade — jadeite and nephrite NaAlSi₂O₆ / Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂ Two different minerals sold under one name. Both are made of densely interlocked fibrous crystals, which makes jade extraordinarily tough — resistant to breaking rather than to scratching — and gives it a slightly greasy lustre and a solid ring when tapped. Size Mohs 6–7 Where Jadeite from Myanmar; nephrite from China, British Columbia, New Zealand. Confused with Serpentine, aventurine quartz and dyed quartzite are all sold as jade. Dyed jadeite, called B-jade, is bleached and resin-impregnated and degrades over years. 20. ### Agate, jasper and carnelian Chalcedony, SiO₂ Microcrystalline quartz. Agate is banded and translucent, jasper is opaque and patterned, carnelian is translucent orange-red. All are hard enough to scratch glass and all take a high polish. Size Mohs 6.5–7 Where Worldwide; abundant in Brazil, Uruguay, Oregon and Montana. Confused with Dyed agate is everywhere — the vivid blue, purple and green slices sold as bookends and coasters are dyed, and the colour is often obvious in the unnaturally even bands. 21. ### Amber Fossilised tree resin Warm to the touch, very light — it floats in saturated salt water — and it takes a static charge when rubbed, picking up small pieces of paper. Often contains insects or plant fragments. Size Mohs 2–2.5 Where The Baltic coast, the Dominican Republic, Myanmar. Confused with Copal, which is young resin and dissolves in acetone, and plastic, which sinks in salt water and smells of burning plastic under a hot pin rather than of pine. 22. ### Pearl Handle with care Nacre — aragonite and conchiolin The tooth test: draw a pearl gently along the biting edge of a front tooth. A real pearl feels distinctly gritty from the microscopic aragonite platelets; an imitation feels perfectly smooth. Size Mohs 2.5–4.5 Where Cultured in Japan, China, Australia and French Polynesia. Risk Soft, porous and destroyed by perfume, hairspray, vinegar and even sweat. Put pearls on last and wipe them after wearing. 23. ### Alexandrite Chrysoberyl, BeAl₂O₄ Green in daylight and red under incandescent light, because its absorption spectrum happens to sit exactly between the two illuminants. Genuine strong-change material is one of the rarest and most valuable gems there is. Size Mohs 8.5 Where Originally the Urals; now Brazil, Sri Lanka, East Africa. Confused with Colour-change synthetic corundum and synthetic alexandrite are both common. Most "alexandrite" sold cheaply is one of these. In the record Mohs 8.5 · BeAl2O4 · orthorhombic · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 24. ### Zircon ZrSiO₄ Very high dispersion and extremely strong double refraction — the doubling of the back facet edges is obvious under a loupe. Heavy for its size. Size Mohs 6–7.5 Where Cambodia, Sri Lanka, Australia. Confused with Entirely unrelated to cubic zirconia despite the name. Zircon is a natural mineral, and the oldest known terrestrial material is a zircon crystal 4.4 billion years old. In the record Mohs 7.5 · Zr(SiO4) · tetragonal · adamantine lustre [check on Macrostrat](https://macrostrat.org/) 25. ### Moissanite SiC — silicon carbide Very close to diamond in hardness and brilliance, but strongly doubly refractive — look through the table with a loupe and the opposite facet edges are visibly doubled. Dispersion is higher, giving more coloured fire. Size Mohs 9.25 Where Almost all material is laboratory-grown. Confused with Sold both honestly as a diamond alternative and dishonestly as diamond. Old thermal-probe testers read it as diamond; modern combined thermal and electrical testers do not. In the record Mohs 9.5 · SiC · hexagonal · vitreous lustre [check on Macrostrat](https://macrostrat.org/) 26. ### Cubic zirconia ZrO₂ Denser than diamond, so a CZ of the same apparent size is noticeably heavier. Facet edges soften with wear because it is softer, and older stones look cloudy where a diamond would still be crisp. Size Mohs 8–8.5 Where Entirely laboratory-grown since the 1970s. In the record Mohs 8 · ZrO2 · isometric · sub-adamantine lustre [check on Macrostrat](https://macrostrat.org/) 27. ### Glass and paste Amorphous silica with additives Rounded rather than crisp facet edges from moulding, gas bubbles visible under a loupe, swirl marks, and warmth — glass reaches skin temperature faster than any crystalline gem. Softer than quartz, so a quartz point scratches it. Size Mohs 5–6 Where Everywhere, in every colour. Confused with Imitates every gem on this list. The bubble check under 10× magnification catches most of it. Nothing in this key matches every filter at once. That usually means one observation is off — a colour read in shade, or a size guessed rather than measured. Clear the filter you are least sure about and look again. ## Four tests you can do with no equipment Professional gem identification uses a refractometer, a polariscope, a spectroscope and a specific-gravity balance. Without any of those, four checks still eliminate most imitations. 1. **Look for gas bubbles under 10× magnification.** Round bubbles mean glass or a plastic. Natural stones contain crystals, fractures and needles, but not spherical bubbles. A cheap loupe is the single most useful gemmological purchase there is. 2. **Check for doubling.** Look through the table at the back facet edges with a loupe. If they appear doubled, the stone is strongly doubly refractive — peridot, zircon, moissanite, tourmaline. Diamond, spinel, garnet and glass never double. 3. **Feel the temperature.** Glass and plastic warm to skin temperature quickly; crystalline gems stay cool because they conduct heat away. Amber is the exception among naturals — it feels warm, and that is diagnostic against glass, which feels cool by comparison. 4. **Heft it.** Density varies enormously and the hand is surprisingly good at it. Cubic zirconia is heavier than diamond, topaz is heavier than quartz, and garnet is heavier than almost anything else red. The one test to skip is scratching. It damages the stone, it is unreliable on a faceted gem, and the popular version of it — scratching glass — separates nothing, because everything from quartz upwards does it. ## Optical effects, and what causes each Several gems are identified by a phenomenon rather than by colour, and each has a specific mechanism. *Optical phenomena in gemstones and the structures that produce them.* | Effect | What you see | Cause | Typical gems | | --- | --- | --- | --- | | Play of colour | Flashes of spectral colour that shift as the stone moves | Diffraction from a regular array of silica spheres | Opal, and nothing else | | Asterism | A four- or six-rayed star | Reflection from oriented needle inclusions | Star ruby, star sapphire, star garnet | | Chatoyancy | A single bright band like a cat's eye | Parallel fibrous inclusions or channels | Chrysoberyl, tiger's eye, tourmaline | | Adularescence | A soft glow that floats under the surface | Light scattering between microscopic feldspar layers | Moonstone | | Labradorescence | A broad flash of peacock colour at one angle | Interference in internal lamellae | Labradorite, spectrolite | | Colour change | A different colour in daylight and lamplight | An absorption spectrum sitting between the two illuminants | Alexandrite, some garnet and sapphire | | Pleochroism | Different colours from different directions | Direction-dependent absorption in the crystal | Tanzanite, iolite, andalusite | The distinction that trips people up is between play of colour and iridescence. Opal's flashes come from a regular internal structure and move independently of the surface; the rainbow on a soap bubble or an oil film is thin-film interference and is a surface effect. Only opal does the first. ## Treated, synthetic, simulant: three different words These are constantly used interchangeably and they mean quite different things commercially and legally. **Treated** means a natural stone modified after mining — heated, irradiated, oiled, dyed or fracture-filled. Treatment is routine and mostly acceptable: essentially all blue topaz is irradiated, nearly all tanzanite is heated, and most emerald is oiled. It must be disclosed, and it affects both value and care instructions. **Synthetic** means grown in a laboratory with the same chemical composition and crystal structure as the natural stone. A synthetic ruby is a ruby by every physical and chemical test, and separating it from a mined one requires a laboratory looking at growth features. It is a real gem, worth far less, and must be disclosed. **Simulant** means a different material that looks like the gem. Cubic zirconia simulating diamond, glass simulating anything, dyed howlite simulating turquoise. These are cheap and identifiable with basic tests. In the United States the Federal Trade Commission requires all three to be disclosed, and a stone described simply as "ruby" must be natural and untreated beyond normal practice. Where a seller is vague, assume treatment. Where a price is far below the market, assume synthetic or simulant. ## Buying without getting caught - **Above a few hundred, get a laboratory report.** GIA, AGS, IGI and, in Europe, Gübelin and SSEF issue reports naming the species, origin where determinable, and every treatment detected. A seller unwilling to allow independent testing is telling you something. - **Ask three specific questions:** is it natural or laboratory-grown, what treatments has it had, and is the weight the total for the piece or for the main stone. Vague answers are the answer. - **Be suspicious of perfect.** Flawless emerald, uniformly perfect turquoise, and evenly coloured amber with a photogenic insect centred in it are all warnings. Natural material has character because it grew in the ground. - **Treat "certified" as meaningless on its own.** Certificates issued by the seller are marketing. The issuing laboratory is the whole content of the claim. - **Do not buy loose stones on holiday.** Gem scams targeting tourists are a well-established industry in several countries, and the recourse afterwards is nil. ## Wearing and cleaning without damaging the stone Hardness governs scratching, and three other properties govern everything else. **Cleavage.** Topaz, tanzanite, fluorite and diamond all have cleavage planes and can split from a single well-placed knock regardless of hardness. This is why an 8-hardness topaz needs a protective setting in a ring. **Porosity.** Turquoise, pearl, opal, coral and amber absorb liquids. Perfume, hairspray, cleaning products and sweat all damage them, and the rule is to put them on last and wipe them after wearing. **Heat and water sensitivity.** Opal holds up to 20% water and crazes if it dries. Emerald is oil-filled. Pearl is a soft organic material. **Never put opal, emerald, pearl, turquoise, amber, tanzanite or coral in an ultrasonic or steam cleaner.** Warm water, mild soap and a soft brush is the right treatment for nearly everything. Storage matters too: harder stones scratch softer ones in a shared box, so a diamond loose in a jewellery box will mark every other stone in it. Individual soft pouches solve it entirely. 27 entries here cover the gems and imitations that come up in practice. There are several thousand mineral species with gem-quality material, and any collection of unusual cut stones will contain things not on this list. For anything that matters financially, the answer is a laboratory report rather than a chart. ## Hardness, formula and crystal system Colour is the least reliable thing about a mineral and hardness is the most reliable, because hardness is a measurement rather than an impression. Every entry in this key that has a formal mineral name is matched against - [Macrostrat](https://macrostrat.org/)'s mineral definitions, which gives 20 of the 27 entries a published Mohs range, a chemical formula, a crystal system and a lustre. The snapshot was taken on 2026-09-04. *Published Mohs ranges for the 20 gemstones in this key, softest at the top. A steel knife blade sits at about 5.5, and it splits the list almost in half: 0 of 20 can be scratched by one, the rest cannot. Turquoise is the softest here and Diamond the hardest. Source: Macrostrat mineral definitions, CC BY 4.0, snapshot 2026-09-04.* Read that figure as a sequence of tests rather than a list of facts. A fingernail is about 2.5 on the Mohs scale and will mark 0 of these 20. A steel knife blade is about 5.5 and splits the rest: 0 can be scratched by one and the remainder cannot, which is a single test that removes most of the list. A piece of quartz at 7 will scratch everything below it. Do the test on a fresh surface and on the specimen rather than the crust, and scratch the mineral with the tool — a streak of metal left on the rock looks like a scratch and is not one. Crystal system is the other free character: 5 of these are trigonal, so the habit you can see in a good specimen narrows the field before any test at all. ### The reference table Formula, hardness range, crystal system and lustre for every named mineral in this key, as published. Where a hardness is given as a range, the mineral genuinely varies — usually with the direction of the scratch or the exact composition. *Published mineral properties for the 20 named entries in this key. Source: Macrostrat mineral definitions, CC BY 4.0, snapshot 2026-09-04. Free to reuse with a link to this page.* | Entry | Formula | Mohs | Crystal system | Lustre | | --- | --- | --- | --- | --- | | Turquoise | Cu(Al,Fe3+)6(PO4)4(OH)8 · 4H2 | 5–6 | Triclinic | Sub-Vitreous, Resinous, Waxy, Dull, Earthy | | Opal | SiO2 · nH2O | 5.5–6.5 | — | Vitreous, Waxy, Greasy, Dull | | Tanzanite | {Ca2}{Al3}(Si2O7)(SiO4)O(OH) | 6–7 | Orthorhombic | Vitreous | | Labradorite | (Ca,Na)[Al(Al,Si)Si2O8] | 6–6.5 | — | Sub-Vitreous | | Garnet | X3Z2(SiO4)3 | 6.5–7.5 | Isometric | vitreous to resinous | | Peridot | (Mg,Fe2+)2SiO4 | 6.5–7 | Orthorhombic | Vitreous | | Amethyst | SiO2 | 7 | Trigonal | Vitreous | | Citrine | SiO2 | 7 | Trigonal | Vitreous | | Tourmaline | A(D3)G6(T6O18)(BO3)3X