Turquoise has been valued as a gemstone for thousands of years, celebrated for its distinctive range of blue and green colors. This opaque mineral holds historical significance across various cultures. A recent surge in popularity has introduced stones marketed as “purple turquoise” into the jewelry market, raising questions about their authenticity. The direct answer is no: purple turquoise does not exist naturally, and its natural chemistry reveals why this color is outside the stone’s genuine color spectrum.
The Natural Chemistry of Turquoise Color
True turquoise is a hydrous phosphate of copper and aluminum, a secondary mineral formed under specific geological conditions in arid regions. The classic blue hue is a direct result of the copper ions present in the mineral’s structure. Color variation occurs based on trace elements that replace the main components. When iron substitutes some of the aluminum, the stone takes on a greenish tint. The natural colors of turquoise are therefore limited to shades spanning from a deep sky blue to a pale, yellowish-green. The combination of elements necessary to produce a purple color simply does not occur in the natural formation process of this mineral.
The Truth About Purple Turquoise Materials
Since natural purple turquoise does not form, the vibrant purple stones seen commercially are the result of human manipulation. These materials fall into two main categories: dyed substitutes and composite products.
The most common purple items are substitutes, where porous, inexpensive minerals like magnesite or howlite are soaked in purple dye. Howlite, a naturally white or light gray mineral, is easily dyed to imitate the color and matrix of turquoise.
The second category involves actual turquoise material that has been significantly altered. For example, “Mohave Purple Turquoise” is a proprietary composite material. It is made by taking fragments of low-grade turquoise, crushing them, and mixing them with a purple-colored resin or epoxy binder. This mixture is sometimes combined with bronze or copper shavings to create an artificial matrix with a metallic sheen. Similarly, “Oyster Turquoise” products often incorporate fragments of spiny oyster shell dyed purple and bound with resin.
Techniques Used to Achieve Purple Hues
The bright purple color is introduced through several processes. The simplest technique is dyeing, which involves immersing porous, light-colored minerals into a dye bath. This allows the dye to penetrate microscopic pores, permanently coloring the material purple.
A more complex method is stabilization, where low-grade turquoise is hardened and colored simultaneously. Since only a small percentage of mined turquoise is hard enough for jewelry, the majority is stabilized by injecting it with polymer resins under high pressure. For purple material, a purple pigment is mixed directly into the resin before infusion, hardening the stone and introducing the hue.
In the creation of composite materials, colored epoxy is used as a binder. Low-quality turquoise pieces are ground into a powder, mixed with the purple-colored resin, and then compressed into solid blocks. The resulting block is cut into cabochons, recognizable by their uniform purple color and often-artificial matrix.
How to Identify Treated and Synthetic Stones
Consumers can use several methods to assess whether a stone is natural, treated, or a substitute.
- Uniformity of color: Naturally occurring turquoise rarely displays a perfectly consistent, flat color. A perfectly saturated, vibrant purple stone without natural variation is highly likely to be dyed or synthetic.
- Price: Purple material is typically priced lower than high-grade, natural blue or green turquoise.
- Hardness and weight: Substitutes like dyed howlite or plastic feel lighter and softer than genuine turquoise, which has a Mohs hardness between 5 and 6.
- Matrix examination: Closely examining the matrix (the dark veins) can expose treatment, as an unnatural, painted-on appearance or dye pooling in surface cracks suggests the stone has been chemically altered.