Turquoise Buying Guide
Revered through the ages for its bright blue hue, turquoise jewelry has come to symbolize protection and hope. Used widely in antique jewelry and often incorporated into innovative modern pieces, this gem will fit into any collection. Better still, it enjoys affordable pricing. Thus, anyone can own a piece of this December birthstone. Although it’s one of the more abundant gemstones, it has a following of its own. Of course, connoisseurs seek rare and extraordinary specimens. Before you make a major turquoise purchase, learn the nuances of turquoise buying.
Turquoise Buying and the Four Cs
The IGS turquoise value listing has price guidelines for turquoise cabochons.
This copper mineral is famous for its blue hues, but shades of blue-green, green, and even yellowish green also occur. Ultimately, a bright blue with little green is the most highly valued color.
Green hues, arising from chromium or vanadium impurities, are less valuable but enjoy their own following. Turquoise with iron has yellow hues. While these hold less value, some artists seek out lime green turquoises for their projects.
If strontium is present, the stone can exhibit a rare secondary purple hue.
Ideally, color should be even and saturated with no visible color zoning. However, color zoning that creates a “bird’s eye” effect, with dark material surrounding light-colored nodules, is valued for its rarity. Arizona’s Turquoise Mountain mine once produced material with this quality.
Additionally, for the highest values, turquoise should have a medium-dark tone. Very dark stones appear dull and uninteresting, while a medium tone allows for the vivid hues coveted in this gem.
Normally a matrix-forming mineral, turquoise is generally opaque. Some high-quality material is translucent. Similarly, crystalline turquoise is extremely rare. In fact, it occurs in only one known locality: Lynch Station, Virginia.
Matrix is often present in turquoise. However, the most valued gems have no visible matrix and exhibit a pure, even color.
Still, the matrix sometimes forms a popular and attractive spider web pattern. Connoisseurs appreciate the variety of matrix and pay top dollar for rare patterns. Black and dark brown matrix is popular because of the intense contrast with the bright blue turquoise. Additionally, red or golden matrix can be quite stunning. However, an unattractive matrix will diminish the stone’s value significantly.
Turquoise stones exhibit different hardness values based on the matrix present. With clay minerals present in the matrix, the stone will be softer and more porous. However, with more silicate minerals, the turquoise is harder and less porous. The range in hardness is extraordinary, reaching as low as 3 and as high as 7.5 on the Mohs scale. Harder stones are more durable and better for setting in jewelry, while treatment to stabilize the stone may be necessary for softer stones. Thus, harder specimens are much more valuable than softer stones.
Cut and Form
Occasionally, fossil pseudomorphs of turquoise form. These are rare and valued for their bright colors and delightful shapes.
“Sea foam” formations arise from small nodules of turquoise without matrix between them. These are attractive in rough but uncommon in nature.
Turquoise geodes are another rare geologic form of turquoise. They make a great addition to a mineral collection.
Large sizes of turquoise are common, though finding a large piece without visible matrix is unusual. Prices don’t climb steeply for larger sizes, though a large matrix-free piece will hold some value for its rarity.
Because some specific mines produce rare, aesthetically pleasing material, a turquoise’s origin may add to its value.
Most of the commercially available turquoise in the United States originates in Chinese mines. While much of this material is low-grade and stabilized, some is high-quality. The Yungai and Zhuxi mines regularly produce high-grade material.
Iran (Persian Turquoise)
Considered the standard for high-quality turquoise, Persian (Iranian) material has a fine blue color. Though once common, these stones rarely appear in today’s market.
Antique Tibetan material turns green with age, due to absorption of skin oils. Fine blue material is rare but available.
Green to greenish blue stones occur in brecciated deposits with significant limonite. These deposits once produced turquoise for the pharaohs. Unfortunately, the color of some material can fade in the sun.
Some large nodules of high-grade turquoise occur in Australia. Their color quality rivals Iranian stones, but the material can shear and break.
The American Southwest is home to many mines, each with their own flavor of turquoise. Consequently, connoisseurs and collectors can sometimes identify the origin mine just by looking at a sample. High-quality stones from rare localities will fetch a good price.
Fox Mine, Nevada
Fox Mine is one of the main sources of American turquoise. Colors range from green to blue, and its hard matrix makes the material good quality.
Sleeping Beauty Mine, Nevada
If you’re looking for a pure blue with little matrix, try Nevada’s Sleeping Beauty Mine. Once heavily mined, material from this source is often found in antique jewelry. However, little modern material is produced.
Royston District, Nevada
For those who prefer stones with character, Royston turquoise may be your style. Shades of blue and green often occur in the same stone. Furthermore, the brown matrix can provide a stunning contrast. Unfortunately, modern production from this mine is small.
Bisbee Mine, Arizona
No turquoise collection is complete without a specimen from Bisbee, Arizona. With medium to intense blue hues that seem to glow from within and a “smoky” matrix, this material is truly stunning. Sadly, the Bisbee Mine is no longer operating, and material is very rare.
Kingman Area, Arizona
Once an important source of turquoise, Kingman now rarely produces high-quality gems. Material from this mine is a light to medium blue with white matrix. However, the white matrix is often dyed black to create contrast with the natural blue colors. In addition, quartz and pyrite crystals are sometimes present, adding a sparkle to the stone.
Carico Lake Mine, Nevada
On the other hand, those looking for green turquoise will delight in gems from Carico Lake, Nevada. Its popular spring green hues are paired with dark spider-webbed matrix. Although you may commonly encounter material from this locality, high-quality gems from here are rare.
Lander Blue Mine, Nevada
With bright blue turquoise and dark spider webbing, the Lander Blue material is striking. However, this deposit is deplorably small. About 100 pounds of material exists, so what is available is valuable and quite rare. Accordingly, buyer beware. Material advertised as Lander Blue may not be authentic.
Number Eight Mine, Nevada
Finally, the Number Eight Mine once produced beautiful specimens with fine red and black spider webbing. Known for its beautiful contrast and occasional large nuggets, Number Eight turquoise is a rare and highly prized gem.
Lower grades of turquoise often receive treatments to improve shine, stability, or color. When searching for a high-quality turquoise, be sure to ask about treatments.
Oil and Wax
Even high-grade turquoise is often coated with wax to protect the porous stone from skin oils that can darken it. Coating with oil or wax also improves the material’s luster and can darken the stone somewhat.
Dyes darken light-toned specimens or light-colored matrix. Sometimes, other minerals are dyed to look like turquoise.
Impregnation with wax, resin, or plastic hardens softer, more porous material. The addition of dyes to this process can simultaneously alter the stone’s color. Stabilization is often necessary to facilitate cutting and polishing. Material that has undergone stabilization is sometimes referred to as “chalk turquoise”.
This proprietary treatment involves soaking turquoise in a solution. The resulting product is less porous and has greater luster. Only detectable by spectroscopy, this method doesn’t involve polymers or dye.
Synthetics and Simulants
Due to turquoise’s popularity, many imitators are on the market.
A mixture of ground turquoise and plastic, this cheap material is easy to cut and readily available.
Though sometimes sold as reconstituted turquoise, this material contains none of the mineral.
Howlite and Magnesite
Dying turquoise is uncommon, but dyed howlite and magnesite are available on the market. Dyes in a variety of colors allow for cheap and vibrant jewelry, but buyer beware. Purple and bright yellow “turquoise” doesn’t contain turquoise. Similarly, “white turquoise” is actually howlite.