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A Field Guide to Southwest Jewelry · by Mateo James

What Is Turquoise? Geology, History, and Why the Southwest

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Turquoise is a secondary copper-aluminum phosphate mineral — chemical formula CuAl₆(PO₄)₄(OH)₈·4H₂O — that forms in arid, high-elevation terrain where copper-bearing and phosphate-bearing groundwater meet. Only about 15 percent of the world's mined turquoise is hard enough to use naturally. The American Southwest is among the planet's most productive and historically significant sources.

A 1915 colour plate of eight polished American turquoises, pale blue to deep blue, some laced with brown and black matrix
Eight American turquoises from named mines, pictured for the U.S. Geological Survey in 1915: pale blue from California (1), dark blue from New Mexico’s Azure mine (4), and matrix from Nevada and Arizona mines (2, 3, 5, 8). Pogue, The Turquois (1915), Frontispiece, figs. 1–8, public domain.

Mateo's Field Notes

The geology is specific: turquoise needs copper deposits, phosphate-bearing rock, arid climate, and altitude. The Basin and Range province delivers all four. Mines cluster between 3,000 and 8,500 feet elevation, where ancient water tables once carved the faulted zones that now yield gem-grade rough.

1915 photograph of a rock specimen with a pale turquoise vein running through it, from Los Cerrillos, New Mexico
A specimen showing a turquoise vein in its host rock, from Los Cerrillos, N. Mex. U.S. National Museum. Pogue, The Turquois (1915), Plate 1, Fig. 2, public domain.

What surprises most learners is how rare usable turquoise actually is. "Natural (untreated) high-grade turquoise is among the rarest of all gemstones, certainly far above diamonds." (Chambless, The Great American Turquoise Rush, p. 175.) The 85 percent of production that is "chalk" — too soft to grind and polish — rarely makes it to a jeweler's bench without treatment.

Native peoples had been mining turquoise in this region for over a thousand years before Anglo settlers identified these deposits in 1857. (Chambless & Ryan.) The mines that eventually made world headlines — Number Eight, Bisbee, Lander Blue, Lone Mountain, alongside the storied Persian fields — each produce material with a distinctive color signature and matrix pattern. Price reflects that rarity: cabochons range from seven cents per carat for low-grade treated material to $1,000 per carat for the finest documented gem-grade stones (Lowry, Turquoise: The World Story, p. 190).

Collector's Handbook

  • Know the formula. CuAl₆(PO₄)₄(OH)₈·4H₂O is not just chemistry — it tells you why turquoise needs copper country: no copper deposits, no turquoise.
  • Assume treatment unless proven otherwise. Because only 15% of production is naturally hard enough to use, stabilized and treated stone dominates the market. Ask for documentation.
  • Mine of origin matters. "Southwest turquoise" is not one material. Number Eight produces golden and black spiderweb; Bisbee is known for deep blue with hard matrix; Lander Blue is among the rarest. Each mine has a price tier.
  • Price anchors. Everyday commercial cabochons under $5/carat; documented gem-grade can reach $1,000/carat. A price claim above $50/carat without provenance documentation is a red flag.
  • Pre-contact history. The thousand-year Native mining tradition pre-dates the Anglo "discovery" by centuries. Jewelry set with named-mine Southwest turquoise by a known Native artist carries both material and cultural provenance.

Related Entries in the Directory

The T.Skies Co-Op Silversmith Directory lists artists who work with named-mine turquoise. Browse by material using the Silversmith Directory.

Primary Sources

  • Lowry, Joe Dan & Joe P. Lowry. Turquoise: The World Story of a Fascinating Gemstone. Gibbs Smith, 2010, p. 190 (price); p. 184 (named mines).
  • Chambless, Philip & Mike Ryan II. Turquoise in America, Part One: The Great American Turquoise Rush 1890–1910. Callais Press, 2021, pp. 80–81 (formation chemistry); p. 175 (rarity statement).

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