Gem library
Turquoise
Desert blue, veined with matrix
Turquoise is a hydrated copper aluminium phosphate and one of humanity's first gems: the Sinai mines were already running under Egypt's first dynasty. Porous and sensitive, it is also one of the most treated stones on the market.
- Hardness (Mohs)
- 5 – 6
- Density
- 2.60 – 2.90
- Crystal system
- Triclinic
- Refractive index
- 1.610 – 1.650
- Cleavage
- Perfect but rarely observable (masses)
Mineralogical identity
- Family
- Phosphates
- Species
- Turquoise
- Chemical formula
- CuAl₆(PO₄)₄(OH)₈·4H₂O
- Crystal system
- Triclinic
- Classification
- Semi-precious stone
- Rarity
- Uncommon
- Indicative price
- €2 – 200/ct depending on quality and mine
Etymology
From the Old French pierre turquoise, «Turkish stone» — not because it was mined there, but because it reached Europe through Turkish merchants from Persia.
Physical & optical properties
- Hardness (Mohs)
- 5 – 6
- Density
- 2.60 – 2.90
- Refractive index
- 1.610 – 1.650
- Birefringence
- 0.040
- Cleavage
- Perfect but rarely observable (masses)
- Fracture
- Conchoidal to splintery
- Lustre
- Waxy to dull
- Diaphaneity
- Opaque
- UV fluorescence
- None
- Pleochroism
- None
- Colours
- sky blue, blue-green, green
Formation, geology & history
Formation in arid climates
Turquoise forms by alteration of aluminium-rich rocks in contact with copper-bearing solutions, in arid regions where water percolates slowly through fractures. It fills those cracks as crusts and nodules, often crossed by host rock: the matrix, brown, black or ochre, which draws the characteristic «spiderweb» networks. The colour depends on copper (blue) and iron (green): Persian turquoise, poor in iron, reaches a pure sky blue, while American and Chinese turquoise often leans green. Its water content explains the mineral's fragility: turquoise that dries out greens and cracks.
Stabilisation and treatments
More than 90 % of turquoise on the market is treated, and you need to know it to buy well. Stabilisation impregnates the porous stone with epoxy resin under vacuum: it hardens, fixes the colour and allows otherwise unusable material to be polished. Wax and oil, traditional treatments, deepen the colour but fade. Dyeing adds artificial blue. Finally, «reconstituted» material binds turquoise powder with resin, and «Neo-Lithe» or «Mojave» turquoise is entirely synthetic. Untreated natural turquoise of high colour is rare and expensive: Sleeping Beauty or Nishapur material can exceed €200/ct.
Five thousand years of use
The Egyptians worked the Sinai from 3000 BC — the inscriptions of Serabit el-Khadim attest to it — and turquoise adorns Tutankhamun's mask. In Persia it covers domes and mosaics and serves as an amulet against falling from horseback. In Mesoamerica the Aztecs inlaid ritual masks with it; in the American Southwest the Navajo and Zuni have made it the heart of their silverwork for centuries. Few stones have such cultural continuity across so many continents.
How to recognise it
- Irregular natural matrixMatrix veins follow real fractures, with random widths and orientations. A regular, drawn network betrays an imitation.
- Slightly porous feelUntreated natural turquoise sticks a little to a moist tongue (a test to perform discreetly). Resin and plastic slide.
- Hardness 5-6 and moderate densityIt is scratched by a steel file but resists a knife. A very light blue stone is howlite; a very dense, cold one is glass.
Imitations, treatments & confusions
- Dyed howliteThe most widespread imitation in the world. Originally white with very fine, regular cobweb black veins, it is dyed blue. Hardness 3.5: a knife scratches it, and the dye bleeds with acetone.
- Reconstituted or synthetic turquoiseTurquoise powder or pigment set in resin (Gilson, Mojave, Neo-Lithe). Over-uniform appearance, over-decorative matrix, lightness, plastic smell on the hot point.
- Dyed magnesite, marble and jasperSold in cheap beads. Test the deposit on cotton with acetone, and the hardness, which is lower than turquoise's.
Deposits & origins
Iran (Nishapur — «Persian» turquoise, the historic benchmark for pure blue), United States (Nevada, Arizona: Sleeping Beauty, Kingman, Bisbee), China (Hubei), Egypt (Sinai, worked for 5,000 years), Mexico, Tibet
Care & precautions
- Never water, never soap: porosity absorbs liquids and the colour turns green.
- No perfume, hairspray, cream or household product on the stone — it absorbs everything and stains permanently.
- Soft dry cloth. Remove turquoise jewellery before showering, swimming and sport.
- Ultrasonic cleaners, steam and heat are absolutely forbidden: turquoise loses its structural water and crazes.
Traditions & crystal healing
- Chakras
- Throat
- Zodiac signs
- Sagittarius · Pisces · Aquarius
- Element
- Air · Water
- Month
- December
A traveller's protective stone in almost every culture that has known it: Persian riders fixed it to the harness, the Navajo associate it with sky and water. Tradition credits it with soothing speech, protecting journeys and acting as an indicator — changing shade to warn its wearer.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Why is my turquoise turning green?
Because it is losing structural water or absorbing oils. The change is common, largely irreversible, and explains the green tone of much antique turquoise.
Turquoise or dyed howlite?
Howlite has very fine, regular cobweb-like black veins, is scratched by a knife, and leaves a blue deposit on cotton soaked in acetone. Turquoise has an irregular brown or ochre matrix.
Is stabilised turquoise a fake?
No. It is genuine turquoise impregnated with resin to make it usable in jewellery. The treatment must be declared, and the stone is worth less than an untreated natural one.