phosphates
Turquoise
CuAl6(PO4)4(OH)8·4H2O
- Also known as
- Persian turquoisesleeping beauty turquoise
- Crystal system
- triclinic
- Hardness
- 5–6 on the Mohs scale
- Lustre
- waxy
- Colour
- Sky blue to green, often with dark matrix veining
- Where it forms
- In arid regions, where groundwater carrying copper reacts with aluminium-rich rock. It needs both a copper source and a dry climate, which is why the deposits are where they are.
- Chiefly from
- Nishapur, IranArizona and Nevada, United StatesHubei, ChinaSinai, Egypt
Why it is that colour
Copper gives the blue; iron substituting for aluminium pushes it green. The greener a turquoise, the more iron it contains, and the trade has historically valued blue over green — a preference with no basis beyond fashion.
Safety
Safe to handle. It is porous and reacts to oils, cosmetics and sweat, which is why old turquoise often turns green — a chemical change rather than dirt.
Where it comes from
Genuinely complicated. Most Arizona and Nevada mines are exhausted or closed, and the great majority of turquoise on the world market is now Chinese, chiefly from Hubei. A very large share of all commercial turquoise is stabilised with resin, and a further share is reconstituted from powder or is dyed howlite or magnesite. Genuinely untreated turquoise is a small fraction of what is sold under the name.
Historical use
Central to Persian, Egyptian, Tibetan and Mesoamerican traditions, and to Navajo, Zuni and Hopi silverwork in the American Southwest, where it carries specific cultural and ceremonial significance and where imitation material sold as Native American work is a long-running and legally actionable problem.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
What is attributed to it, and since when
One of the oldest documented gemstones, mined in Sinai by the Egyptians before 3000 BC and in Iran for at least as long. Persian tradition treats it as protective against misfortune, and the belief that it changes colour to warn its wearer of illness or danger appears in medieval European and Persian sources alike. That belief has a real basis: it genuinely does change colour, for chemical reasons.
Described, not endorsed. Dating a claim is not the same as assessing it — but an association that first appears in a book published in 1985 is not an ancient inheritance, whatever the label says. A sincere account of feeling better is compatible with the stone doing nothing — see the placebo effect.
Sold as this, but not
Worth knowing
The colour-changing belief is the most interesting thing here, because it is one of the very few old stone beliefs with a physical mechanism behind it. Turquoise is porous. It absorbs skin oils, soap, perfume and sweat, and the copper chemistry shifts as it does, so a stone worn against the skin for years genuinely turns from blue toward green. Someone whose turquoise changed had observed something real; the interpretation, that it was warning them, is the part that was added.
The authenticity problem is severe enough that the United States has federal legislation about it. The Indian Arts and Crafts Act makes it unlawful to sell goods as Native American-produced when they are not, and turquoise jewellery is one of the main categories it exists for.
Identity checked against IMA-CNMNC master list, June 2025.