Key properties
| Chemical formula | CuAl6(PO4)4(OH)8·4H2O |
| Crystal system | Triclinic |
| Mohs hardness | 5-6 |
| Toughness | Fair to good in gem grades; poor in chalky untreated material |
| Refractive index | 1.610-1.650 |
| Optic character | Aggregate (AGG) of a doubly refractive triclinic mineral — reads as a single spot about 1.61-1.62 |
| Specific gravity | 2.40-2.90 |
| Cleavage | Perfect to good in two directions — never seen in the massive gem material |
| Fracture | Conchoidal to granular depending on porosity; chalky material crumbles |
| Habit | Massive nodules, veins, seams and crusts; microcrystals rare |
| Lustre | Waxy to subvitreous; polish: Waxy to vitreous in low-porosity gem grades |
| UV fluorescence | Inert to weak greenish yellow in LW UV; inert in SW UV |
| Pleochroism | None |
| Cause of colour | Blue from copper (Cu2+); green tones where iron (Fe3+) substitutes for aluminium in the same structure |
| Typical inclusions | Dark brown to black matrix (limonite, sandstone, shale) as blotches and 'spiderweb' vein networks; pyrite in some Iranian material |
| Stability | Stable to light, but heat makes it decrepitate, brown and even flake apart. Slowly soluble in hydrochloric acid. Perspiration, skin oils, cosmetics and even heavy liquids can discolour it |
| Heat sensitivity | Extreme — never steam, torch or hot ultrasonic |
| Care and cleaning | Wipe with a soft cloth after wear; brief warm soapy water only; never ultrasonic or steam. Put turquoise jewellery on last, remove first |
| Birthstones | December (with zircon and tanzanite); 11th wedding anniversary in traditional US lists |
| Availability | Plentiful as stabilised and treated material; fine natural untreated turquoise scarce and mine-named |
| Recognition | Well known — a household name with 5,000+ years of history from Egypt to the American Southwest |
Varieties
Turquoise
| Colour | light to medium sky blue, greenish blue to green; often mottled or veined with dark matrix |
| Transparency | opaque |
| Clarity type | Opaque — graded by colour, matrix pattern and degree of treatment, not clarity |
| Phenomena | None |
| Appearance | Robin's-egg to sea-green with waxy polish; matrix runs from clean even blue (Sleeping Beauty) to dense brown-black spiderweb (Number 8, Lander Blue) |
| Trade names | Persian (even medium blue, the historic finest) • Sleeping Beauty (Globe, Arizona — matrix-free sky blue, mine closed 2012) • Kingman (Arizona) • Bisbee (Arizona, historic) • Morenci (Arizona) • Royston • Carico Lake • Number 8 • Lander Blue (Nevada mine names, collectors' grades) • spiderweb (matrix pattern grade) |
| Misnomers | 'Persian' applied loosely to any even blue • reconstructed/block turquoise sold as natural (powder plus binder) • 'Persian/Sleeping Beauty' labels on stabilised or reconstituted stone |
| Typical sizes | Cabochons from a fraction of a carat to very large; beads; inlay strips; nugget strands |
| Cutting styles | Cabochons • beads • carvings • inlay • nuggets • tablets |
| Key separations | Spot RI about 1.61-1.62, waxy lustre, SG about 2.4-2.9. vs dyed howlite/magnesite: white body shows at chips and drill holes, dye in surface pits, howlite RI about 1.586. vs variscite: RI about 1.57, greener, yellow-brown matrix, 688 nm line. vs Gilson synthetic: speckled blue-white under magnification, no natural matrix. vs odontolite (fossil bone): organic texture. vs prosopite: different locality pattern and RI |
| Sources (localities) | Iran (Nishapur/Neyshabur, Khorasan) • USA: Arizona (Kingman, Sleeping Beauty/Globe, Morenci, Bisbee) and Nevada (Lander County: Carico Lake, Lander Blue; Royston, Number 8) • China (Hubei — main mine reportedly closed 2019) • Egypt (Sinai: Wadi Maghareh, Serabit el-Khadim — historic) • Mexico • Chile • Australia • Tibet • Afghanistan |
| Availability | Plentiful (largely treated); natural fine material mine-named and scarce |
| Market notes | Treatment disclosure drives value: natural American mine-run stones can outprice per-carat many transparent gems, while stabilised commercial turquoise sells for dollars. Sleeping Beauty stock appreciated after the 2012 closure |
| Care notes | Cosmetics, perspiration and pool chlorine turn blue material green; wipe after wear, string beads with knots; avoid all chemicals and heat |
| In short | The December birthstone: copper-blue, waxy, porous and endlessly treated. Bench identification is easy (spot RI about 1.61), but the professional value question is which treatment, which mine, and what disclosure. |
| Size (ct) | USD per carat | Tier | As of |
|---|---|---|---|
| 1.00–10.00 | $1.00 – $10.00 | stabilised/dyed commercial cabs and beads | 2026-10-26 |
| 1.00–10.00 | $20.00 – $200.00 | natural untreated gem grades (Kingman, Sleeping Beauty stock) | 2026-10-26 |
| 1.00–10.00 | $200.00 – $1000.00 | collectors' mines: Bisbee, Lander Blue, Number 8 | 2026-10-26 |
Retail market survey, per carat unless noted. Ranges describe what commercial to fine stones trade at; exceptional stones and provenance premiums sit above them.
Sources
GIA gem encyclopedia · mindat.org · Wikipedia
Data compiled and fact-checked against gemmological literature, October 2026 (JDMIS gem reference). Properties are ranges accepted in gemmological practice; individual stones vary.
See also
Gemstone reference entries: gem #56 · gem #89
Related materials: Variscite
Identification wizard · All 83 materials · Singapore gem labs