Do you know What is Turquoise?
Turquoise is an opaque mineral that occurs in beautiful hues of blue, bluish green, green, and yellowish green. It has been treasured as a gemstone for thousands of years. Isolated from one another, the ancient people of Africa, Asia, South America and North America independently made turquoise one of their preferred materials for producing gemstones, inlay, and small sculptures.
Chemically, turquoise is a hydrous phosphate of copper and aluminum (CuAl6(PO4)4(OH)8·5H2). Its only important use is in the manufacture of jewelry and ornamental objects. However, in that use it is extremely popular – so popular that the English language uses the word “turquoise” as the name of a slightly greenish blue color that is typical for high-quality turquoise.
Very few minerals have a color that is so well known, so characteristic, and so impressive that the name of the mineral becomes so commonly used. Only three other minerals – gold, silver, and copper – have a color that is used more often in common language than turquoise.
Blue minerals are rare, and that is why turquoise captures attention in the gemstone market. The most desirable color of turquoise is a sky blue or robin’s-egg blue. Some people inappropriately describe the color as “Persian blue” after the famous high-quality material mined in the area that is now known as Iraq. Using a geographic name with a gem material should only be done when the material was mined in that locality.
After blue, bluish green stones are preferred, with green and yellowish green material being less desirable. Departure from a nice blue color is caused by small amounts of iron substituting for aluminum in the turquoise structure. The iron imparts a green tint to the turquoise in proportion to its abundance. The color of turquoise might also be altered by small amounts of iron or zinc substituting for copper in the turquoise structure.
Some turquoise contains inclusions of its host rock (known as matrix) that appear as black or brown spider-webbing or patches within the material. Many cutters try to produce stones that exclude the matrix, but sometimes it is so uniformly or finely distributed through the stone that it cannot be avoided. Some people who purchase turquoise jewelry enjoy seeing the matrix within the stone, but as a general rule, turquoise with heavy matrix is less desirable.
Some turquoise localities produce material with a characteristic color and appearance. For example, the Sleeping Beauty Mine is known for its light blue turquoise without matrix. Much of the turquoise from the Kingman Mine is bright blue with a spider web of black matrix. The Morenci Mine produces a lot of dark blue turquoise with pyrite in the matrix. Much of the Bisbee turquoise has a bright blue color with a chocolate brown matrix. People who know turquoise can often, but not always, correctly associate a stone with a specific mine.
Protecting Turquoise Color with Proper Cleaning
The color of turquoise can be altered by improper care and cleaning. If you own turquoise jewelry with a nice color, you should be careful about exposing it to prolonged sunlight, heat, cosmetics, perspiration, and body oil. If it has been exposed to cosmetics, perspiration or body oil simply clean it gently with a soft cloth that is wet with a very mild soap solution, followed by cleaning with a soft cloth that has been dampened with plain water. Then after the turquoise is dry, store it in a jewelry box away from bright light or heat.
Turquoise is rarely found in well-formed crystals. Instead it is usually an aggregate of microcrystals. When the microcrystals are packed closely together, the turquoise has a lower porosity, greater durability, and polishes to a higher luster. This luster falls short of being “vitreous” or “glassy.” Instead many people describe it as “waxy” or “subvitreous.”
Turquoise forms best in an arid climate, and that determines the geography of turquoise sources. Most of the world’s turquoise rough is currently produced in the southwestern United States, China, Chile, Egypt, Iran, and Mexico.
In these areas, rainfall infiltrates downward through soil and rock, dissolving small amounts of copper. When this water is later evaporated, the copper combines with aluminum and phosphorus to deposit tiny amounts of turquoise on the walls of subsurface fractures.
Turquoise can also replace the rock in contact with these waters. If the replacement is complete, a solid mass of turquoise will be formed. When the replacement is less complete, the host rock will appear as a “matrix” within the turquoise. The matrix can form a “spider web,” “patchy” design, or other pattern within the stone.