On the nature of turquoise
Dry, barren regions are home to the legendary turquoise gemstone -- places where acidic groundwater interacts with minerals containing elements of phosphorus and aluminum. This is the sedimentary process that gives birth to the opaque, blue to green mineral that mankind has loved for thousands of years... a compound of hydrated copper and aluminum phosphate... turquoise.
Did you know that copper is responsible for the blue shades in turquoise, while traces of iron result in green?
Popular as a gem since ancient times, turquoise is quite possibly one of the oldest decorative stones used by mankind. Egyptian mines were supplying turquoise more than 6,000 years ago. It was treasured by Aztecs and Incas and later by the Native Americans. Its name derives from Old French. Pierre Turquoise meaning “stone of Turkey” referred to the large piles of Persian turquoise sold in Turkish markets.
On finding turquoise and what to look for
Turquoise is usually found in arid climates. For example, major deposits of this sacred mineral have been mined in Iran (also known as Persia), northwest China, the Sinai Peninsula in Egypt, and the American Southwest.
In the American Southwest, there are approximately twenty mines that produce what is considered gem-quality turquoise. While most of these mines are located in Nevada, a few others are situated in Arizona, Colorado, and New Mexico. Over time, many deposits in the Southwest have been depleted and the mines closed. Restrictions imposed by the government and the high costs associated with mining have also interfered with the ability to discover high quality turquoise. Interestingly, much of the turquoise coming out the ground today is recovered as a byproduct of copper mining.
The value of a turquoise is determined by its color, texture, and the presence or absence of matrix.
Color. Turquoise gemstones can range from semi-translucent to opaque. Typically, they can be found in colors of light to medium blue or greenish-blue. Turquoise is often mottled or has dark splotches. These qualities do not bode well for the value of stone. Thus, in turquoise, an even, vivid, medium blue is generally considered the most valuable. That said, some people do prefer the stones with a greenish-blue cast. Heating turquoise can result in various shades of green such as avocado and lime -- and these unusual stones are actively sought by contemporary designers.
Matrix. Matrix is a remnant of a gemstone's surrounding rock and it is common for turquoise to have veins of matrix running through it. The specimens known as spider web turquoise exhibit delicate seams of matrix that form fascinating motifs reminiscent of a spider's web. Although these patterned stones are very attractive and quite desirable, the most valuable turquoise has no matrix at all.
Texture. Turquoise is an aggregate of microscopic crystals. When the crystals are densely packed, the stone tends to be less porous resulting in a finer texture that develops a pretty, waxy luster after polishing. Turquoise with a looser crystal structure is more porous and that means a coarser texture and a dull luster.
Another factor to keep in mind is that turquoise is a relatively soft gemstone. It registers 5 or 6 on the Mohs Scale of Hardness. Turquoise that has a coarser texture usually falls lower on the scale -- it is softer and less durable than a stone with a finer texture which ranks higher.
Historical notes and other interesting facts about turquoise
Ancient Egypt. Turquoise has been found in Egyptian tombs dating to 4000 B.C. The ancient Egyptians called turquoise mefkat, which also meant "joy" and "delight." Probably the most recognizable piece is the gold burial mask of Tutankhamen, which is inlaid with turquoise, lapis lazuli, carnelian and colored glass. It was also set into rings and great sweeping necklaces called pectorals -- and often carved in a scarab pattern.
Hathor. Her name means mansion of Horus and she is an ancient goddess of the Egyptians who symbolized joy, feminine love, and motherhood. She was one of the most important and popular deities in Ancient Egypt. She was also the patroness of Serabit el-Khadim, where turquoise was once mined. Her titles included "Lady of Turquoise" and "Mistress of Turquoise."
Chinese carvings. More than 3000 years ago, Chinese artisans were using turquoise in their carvings.
Quetzacoatl's favorite. When Montezuma, ruler of the Aztec Empire, first met the conquistador, Cortes, he thought he was the deity, Quetzalcoatl, and gifted him with the god’s favorite gem: turquoise.
Symbol of the American Southwest. We all probably know that turquoise was used by Native American tribes in jewelry and amulets but did you know that they also used it as a medium of exchange? And not only that! Apache Indians also attached turquoise to their bows and firearms to increase accuracy.
Persian Palaces. Turquoise was used to decorate the domes of palaces in Persia. Its vibrant blue color was considered a symbol of heaven on earth. It was also used to adorn all kinds of objects such as turbans and bridles.
Ceremonial masks. The Aztecs embellished masks, knives, and shields with inlaid turquoise as well as gold, quartz, malachite, jet, jade, coral, and shells.
Victorians. Turquoise was well loved by the Victorians and frequently used during this era in jewelry.
Lucky stone. Turquoise has long been Tibet's national gemstone. It is believed to ensure good health, good fortune, and to ward away evil.
Resources and further reading
The Gemological Institute of America's Gem Encyclopedia.
Gemstones of the World. By Walter Schuman. Our go to book at Grimballs.
Jewels: A Secret History. By Victoria Finlay. An non-fiction adventure through time and place exploring the history of gems.
Smithsonian Institution National Museum of Natural History's Gem Gallery.
Wikipedia's entry on Turquoise.