Fox Turquoise
Fox Turquoise
A prized Nevada locality known for vivid blue colour and distinctive dark matrix
Fox turquoise is a variety of turquoise mined from the Fox Mine in Lander County, Nevada, and is regarded among collectors and the American Southwest jewellery trade as one of the finer Nevada locality materials. Characterised by a bright, saturated blue to blue-green body colour and a well-defined dark matrix — typically of black or dark brown chert or ironstone — Fox turquoise at its best combines visual clarity with the kind of hardness that allows a high, glassy polish. Though the mine's most productive period fell in the mid-twentieth century, material from the Fox locality continues to circulate in the secondary market and commands a premium among connoisseurs of American turquoise.
Geological Setting and Locality
Lander County, in the central Great Basin of Nevada, sits within a region of intense hydrothermal alteration associated with Palaeozoic and Mesozoic volcanic and sedimentary sequences. Turquoise forms in this environment through the percolation of copper-bearing groundwater through aluminium-rich host rock — typically rhyolite, tuff, or chert — depositing the hydrated copper aluminium phosphate mineral along fractures and in nodular masses. The Fox Mine exploits veins and seams within a chert-dominant host, which accounts for the characteristic dark, fine-grained matrix that threads through the blue material. This matrix is considered aesthetically desirable when it forms crisp, spider-web or irregular geometric patterns against the blue ground, and such specimens are among the most sought-after from the locality.
Nevada as a whole is the most significant turquoise-producing state in the United States, with dozens of named localities including Royston, Carico Lake, Pilot Mountain, and Lone Mountain, each with a recognisable colour and matrix signature. Fox turquoise occupies a respected position within this canon, distinguished from neighbouring localities by its particular shade of blue — leaning toward a pure, slightly greenish blue rather than the sky blue of some Sleeping Beauty material or the distinctly green hues of Carico Lake.
Physical and Optical Properties
Turquoise is a hydrated copper aluminium phosphate with the chemical formula CuAl₆(PO₄)₄(OH)₈·4H₂O. It crystallises in the triclinic system but is almost invariably found in cryptocrystalline, massive, or nodular form rather than as discrete crystals. The relevant properties for Fox turquoise fall within the standard ranges for the species:
- Colour: Bright blue to blue-green, often described as a medium to medium-dark tone with good saturation.
- Hardness: Approximately 5 to 6 on the Mohs scale; Fox material is generally considered to be on the harder end for Nevada turquoise, though this varies by individual piece.
- Lustre: Waxy to subvitreous; high-quality natural material takes a smooth, glassy polish.
- Specific gravity: Typically 2.60–2.85, depending on porosity and matrix content.
- Refractive index: Approximately 1.61–1.65 (spot reading, given the massive habit).
- Matrix: Dark chert or ironstone, ranging from sparse veining to dense spider-web patterning.
The colour of turquoise is primarily a function of copper content, with iron substitution shifting the hue toward green. Fox turquoise tends to maintain a blue dominance, suggesting relatively low iron substitution in the aluminium sites of its crystal structure.
Treatment and Stabilisation
A significant proportion of Fox Mine production — as with most American turquoise localities — was of insufficient hardness or structural integrity to be used in jewellery without enhancement. Stabilisation, the most common treatment applied to turquoise, involves impregnating porous rough with a colourless resin or polymer under vacuum and pressure. The process improves hardness, reduces susceptibility to discolouration from skin oils and cosmetics, and allows material that would otherwise be too friable to be cut and polished. Stabilised Fox turquoise retains the colour and matrix appearance of the natural material but is considered less valuable than untreated natural Fox turquoise of equivalent quality.
A smaller quantity of Fox Mine material was of sufficient quality to be used in its natural, untreated state — referred to in the trade as natural or natural hard turquoise. Such pieces are correspondingly rarer and more valuable, particularly when accompanied by documentation of provenance. Collectors and serious buyers are advised to seek laboratory verification, as the distinction between natural and stabilised turquoise requires infrared spectroscopy or similar analytical methods and cannot be reliably made by visual inspection alone. GIA's gemological laboratory and other accredited facilities offer turquoise testing that can identify resin impregnation and assess treatment status.
Dyed turquoise and simulants — including howlite and magnesite dyed to imitate turquoise — are also encountered in the market, though these are distinct from stabilised genuine turquoise and represent a more significant misrepresentation. Buyers of Fox turquoise specifically should be attentive to provenance claims, as the name carries market value and may be applied loosely.
History and Cultural Significance
The Fox Mine was active primarily during the mid-twentieth century, a period that coincided with a broader boom in the American turquoise trade and a sustained demand from Native American silversmiths — particularly Navajo, Zuni, and Pueblo artists — who incorporated turquoise into silverwork of enduring cultural and artistic importance. Fox turquoise, with its reliable colour and matrix character, was among the materials favoured by these craftspeople, and vintage pieces set with documented Fox material are collected both as jewellery and as works of ethnographic and artistic significance.
The American turquoise trade of the mid-twentieth century was also shaped by a network of traders, miners, and dealers who established the locality names and quality hierarchies still in use today. Fox turquoise's reputation was built during this period and has been sustained by the relative scarcity of new production and the continued desirability of its colour profile.
In the Trade
Fox turquoise is traded primarily as rough, cabochons, and finished jewellery in the American Southwest market, at specialist gem shows such as the Tucson Gem and Mineral Show, and through dealers specialising in American turquoise. Natural, untreated Fox turquoise of fine colour and spider-web matrix commands prices well above stabilised material and above generic Nevada turquoise without locality attribution. Collectors place particular value on documented rough or cut stones with clear provenance, and on vintage jewellery pieces where the Fox origin can be substantiated.
As with all turquoise localities where active mining has ceased or diminished, the supply of genuine Fox turquoise is finite. This scarcity, combined with the material's established reputation, supports its continued position as a collectible locality variety rather than a commodity gemstone.