The stone marketed as “African Turquoise” often confuses jewelry buyers because its attractive blue-green coloration and dark matrix patterns closely resemble high-grade natural turquoise. However, the mineralogical identity of this material is distinct from the traditional gemstone. It is a case of a descriptive trade name rather than a true mineral classification, a difference rooted in the stone’s fundamental chemical composition and geological origin.
The True Mineral Identity
The material sold under the trade name “African Turquoise” is not a member of the turquoise mineral family. It is a variety of jasper, which is a form of chalcedony, a microcrystalline type of quartz. This places it firmly within the silicate mineral class, sharing its basic structure with other common stones like agate and amethyst.
Jasper is an opaque rock, often exhibiting a mottled or speckled appearance due to various mineral inclusions. For the stone to display its characteristic teal or greenish-blue color, it must contain trace amounts of copper minerals. The dark, web-like matrix, which is a significant part of its visual appeal, is typically formed by inclusions of iron compounds or other host rock fragments.
The stone is sourced primarily from deposits within Africa, which explains the geographical part of its commercial name. While the exact geological location can vary, the material is generally a naturally occurring jasper that is sometimes treated or dyed to enhance the blue-green color to better mimic genuine turquoise. Its inherent composition as a type of quartz makes it harder and more durable than true turquoise, rating between 6.5 and 7 on the Mohs scale.
Chemical Differences from Genuine Turquoise
The distinction between “African Turquoise” and true turquoise is confirmed by examining their unique chemical formulas. Genuine turquoise is scientifically classified as a hydrous copper aluminum phosphate. The presence of copper is responsible for the stone’s blue hue, while aluminum and phosphate form the bulk of its structure.
“African Turquoise” (jasper) is fundamentally composed of silicon dioxide (\(\text{SiO}_2\)). This composition is the basis of the silicate mineral group, a completely different class from the phosphate group that defines true turquoise. The color in this jasper results from copper and iron impurities within the \(\text{SiO}_2\) matrix, not from copper being a core structural element.
The hardness difference results from this chemical disparity, with the quartz-based jasper being tougher than the softer phosphate-based turquoise, which typically measures 5 to 6 on the Mohs scale. The two stones are not chemically related; they merely share a similar aesthetic due to the presence of copper in both, albeit in different structural roles.
Trade Names and Ethical Buying
The use of the name “African Turquoise” is an example of a descriptive trade name applied to a less-expensive stone to connect it visually to a more valuable one. This practice attracts consumers seeking the look and color of turquoise without the high cost. Jasper is significantly less valuable than high-grade, naturally blue turquoise, a difference that should be reflected in the final retail price.
Consumers should understand that while descriptive names are common, organizations like the Federal Trade Commission (FTC) in the United States have guidelines emphasizing transparency. These guidelines suggest that when a material is sold under a trade name, the seller must clearly disclose the true identity of the stone, often by using the term “African Turquoise Jasper” or by stating that it is a type of jasper.
To make informed purchases, consumers should ask sellers directly about the mineral identity, not just the trade name, and inquire about any treatments like dyeing. One physical clue is that the matrix in genuine turquoise is often a delicate spider-webbing, while the matrix in this jasper is often larger, more speckled, or linear. Knowing that the stone is a quartz-based jasper allows buyers to appreciate its own merits while ensuring they are paying a fair price for a durable and attractive stone.