Dyed howlite is a white-to-cream calcium borosilicate mineral, Ca₂B₅SiO₉(OH)₅, that has been artificially coloured — most commonly in shades of sky blue, turquoise, or teal — to simulate natural turquoise. The treatment exploits howlite's unusually high porosity, which allows dye to penetrate deeply and evenly, and its naturally occurring grey-to-black veining, which closely mimics the matrix patterns characteristic of genuine turquoise. The result is a material that, to the untrained eye and in casual retail settings, can be convincingly mistaken for one of the most historically significant gemstones in the world. Dyed howlite is not inherently fraudulent — it is a legitimate, inexpensive decorative material — but its widespread mis-labelling and mis-selling as natural turquoise make it one of the most consequential identification challenges in the trade for stones at the lower end of the market.

Howlite: The Host Material

Howlite was first described in 1868 by the Canadian geologist Henry How, who identified it in gypsum deposits in Nova Scotia. It belongs to no major mineral group and is classified as a borate mineral with a monoclinic crystal system, though it almost invariably occurs in massive, nodular, or cauliflower-like aggregates rather than distinct crystals. In its natural state it is white or very pale grey, with irregular grey or black veining produced by inclusions of other minerals. Its hardness on the Mohs scale is approximately 3 to 3.5 — considerably softer than turquoise, which registers 5 to 6 — and its specific gravity ranges from approximately 2.53 to 2.59, notably lower than turquoise's 2.60 to 2.90. These physical differences are among the primary diagnostic tools used to distinguish dyed howlite from its target simulant.

The mineral's porosity — a consequence of its fine-grained, chalky microstructure — is the property that makes it so receptive to dyeing. Dye solutions penetrate the material readily and, once set, produce a colour that is stable under normal handling and ambient conditions. Commercially significant deposits are found in the United States (notably California and Nevada), Canada, Germany, Mexico, and Turkey.

The Dyeing Process

The dyeing of howlite is a straightforward industrial process. Rough or pre-cut material is typically immersed in an aqueous or alcohol-based dye solution — most often a blue or blue-green organic or synthetic dye — for a period ranging from hours to several days, depending on the depth of colour desired and the porosity of the particular batch. The material may be gently heated to encourage dye uptake. After dyeing, the surface is sometimes sealed with a wax, resin, or lacquer coating to stabilise the colour, reduce surface abrasion, and impart a more polished appearance. This secondary coating, when present, adds another layer of treatment that should be disclosed.

The resulting colour can range from pale robin's-egg blue to deep teal, and the grey veining of the host material reads convincingly as the dark matrix of turquoise from localities such as the Nishapur mines of Iran or the Sleeping Beauty mine of Arizona. Some dyed howlite is also coloured red or orange to simulate coral, or black to simulate jet or onyx, though the turquoise simulant application is by far the most commercially prevalent.

Identification

Gemmological identification of dyed howlite relies on a combination of physical testing, chemical analysis, and microscopic examination. No single test is definitive in isolation, but the following battery of observations is reliable:

• Specific gravity: Dyed howlite measures approximately 2.53–2.59, falling below the typical range for natural turquoise (2.60–2.90). Hydrostatic weighing or heavy-liquid testing will reveal this discrepancy.
• Hardness: At 3 to 3.5 on the Mohs scale, howlite is noticeably softer than turquoise. A careful scratch test on an inconspicuous area will distinguish the two, though this is a destructive method and should be used judiciously.
• Dye concentration under magnification: Examination under a loupe or gemological microscope typically reveals dye pooling in surface fractures, grain boundaries, and porous zones. The colour distribution is uneven at the microscopic level in a way that natural colouration is not. Dye may also bleed slightly onto a cotton swab moistened with acetone or alcohol — a simple and non-destructive spot test that can indicate the presence of an organic dye.
• Chemical testing for copper: Natural turquoise owes its colour to copper (and sometimes iron) in its chemical composition — it is a hydrated copper aluminium phosphate. Howlite contains no copper. A spot test using ammonia or other copper-detecting reagents will yield a negative result for dyed howlite. Advanced laboratories use energy-dispersive X-ray fluorescence (EDXRF) or other spectroscopic methods to confirm the absence of copper definitively.
• Refractive index: Turquoise has a refractive index of approximately 1.61–1.65. Howlite's RI is lower, around 1.583–1.608, though the massive habit of both materials makes precise RI measurement difficult on polished cabochons.
• Infrared spectroscopy: FTIR analysis readily distinguishes howlite from turquoise on the basis of their differing molecular structures and can also identify the presence of wax or resin coatings.

GIA's gem identification laboratory and other major gemmological laboratories — including Gübelin Gem Lab, SSEF, and Lotus Gemology — routinely identify dyed howlite through combinations of the above methods. The material does not present a serious identification challenge for a trained gemmologist equipped with standard instruments.

Market Context and Disclosure

Dyed howlite occupies a peculiar position in the gem trade. As a dyed simulant sold honestly and at appropriate price points, it is entirely legitimate: inexpensive beaded bracelets, necklaces, and decorative objects made from dyed howlite are sold openly and legally throughout the world. The material has genuine decorative appeal and serves a market that desires the aesthetic of turquoise without the cost of the genuine article.

The problem arises when dyed howlite is sold — whether through ignorance or deliberate misrepresentation — as natural turquoise. This occurs with particular frequency in tourist markets, street stalls, and online marketplaces, where buyers lack the means to test the material and sellers may themselves be unaware of what they are handling. The price differential is substantial: fine natural turquoise, particularly material from Nishapur (Iran), the Lander Blue mine (Nevada), or Bisbee (Arizona), commands prices per carat that are orders of magnitude higher than dyed howlite, which is available in wholesale quantities for a few dollars per kilogram.

Industry bodies including the International Colored Gemstone Association (ICA) and the American Gem Trade Association (AGTA) require disclosure of all treatments, including dyeing, as a condition of membership and ethical trading. The AGTA's Gemological Testing Center explicitly lists dyed simulants as a category requiring full disclosure at point of sale. In many jurisdictions, selling dyed howlite as natural turquoise without disclosure constitutes consumer fraud under applicable trade description or consumer protection legislation.

It is worth noting that howlite is not the only material dyed to simulate turquoise. Magnesite, a magnesium carbonate mineral with similarly porous structure and white colouration, is also widely dyed for this purpose, as are certain chalcedony and jasper varieties. Stabilised turquoise — genuine turquoise impregnated with resin to improve durability and colour — occupies a further intermediate category. The full spectrum of turquoise simulants and treatments is a subject of ongoing attention in gemmological literature.

A Note on Value and Collecting

Dyed howlite, properly identified and sold as such, is not without merit as a decorative material. Its even colour, workability, and low cost make it suitable for high-volume jewellery production, craft applications, and educational purposes. Gemmology students frequently use dyed howlite as a reference specimen precisely because it is so commonly encountered and because distinguishing it from turquoise is a foundational identification exercise. The material should be assessed and priced on its own terms — not disparaged for failing to be something it was never claimed to be, and not misrepresented as something it is not.

Further Reading

• GIA — Turquoise Simulants and Identification
• AGTA Gemological Testing Center — Treatment Disclosure Policy
• International Colored Gemstone Association — Turquoise