Azure sky, robin’s egg blue: Vivid shades of turquoise define the color that’s named after this gem.
Turquoise is found in only a few places on earth: dry and barren regions where acidic, copper-rich groundwater seeps downward and reacts with minerals that contain phosphorus and aluminum. The result of this sedimentary process is a porous, semitranslucent to opaque compound of hydrated copper and aluminum phosphate.
Turquoise is a prime example of an opaque colored stone that can be marketed both as a gem for jewelry and as an ornamental material.
Turquoise might lack the sparkle and clarity of transparent colored gemstones like ruby, emerald, and sapphire, but its multi-layered history and soul-satisfying color make it a desirable gem. Its color can range from dull greens to grass greens to a bright, medium-toned, sky blue. People value turquoise highly for its combination of ancient heritage and unforgettable color.
The traditional source for the top color, sometimes described as robin’s-egg blue or sky blue, is the Nishapur district of Iran, the country formerly known as Persia. So, quite often, you’ll hear people in the trade call turquoise of this beautiful color “Persian blue,” whether or not it was actually mined in Iran.
Top-quality turquoise has inspired designers to create elegant jewelry. It’s most often cut into cabochons, but it might also be cut into beads or flat pieces for inlays.
Although much turquoise jewelry is sleek and modern, many US consumers are familiar with the traditional jewelry of Native American peoples such as the Pueblo, Hopi, Zuni, and Navajo. People interested in Native American arts and crafts frequently collect this stylized silver jewelry.
Turquoise is relatively soft, so it’s ideal for carving. Artists in Europe, Asia, the Middle East, and the Americas choose turquoise as a medium for carved jewelry and art objects. It’s often fashioned into talismans with Native American significance, such as bird and animal carvings, called fetishes.
Turquoise owes its texture to its structure and composition. It’s an aggregate of microscopic crystals that form a solid mass. If the crystals are packed closely together, the material is less porous, so it has a finer texture. Fine-textured turquoise has an attractive, waxy luster when it’s polished. Turquoise with a less-dense crystal structure has higher porosity and coarser texture, resulting in a dull luster when it’s polished.
Porosity and texture don’t just affect appearance: They also affect durability. Turquoise is fairly soft—it ranks 5 to 6 on the Mohs scale. Turquoise with a coarse texture might have poor toughness, too. Samples with finer texture have fair to good toughness.
In turquoise, low porosity and fine texture are more valuable than high porosity and coarse texture. Coarse, porous stones are usually treated to make them smoother, shinier, and more marketable.
Turquoise deposits usually form in iron-rich limonite or sandstone. Limonite creates dark brown markings in turquoise, while sandstone creates tan markings. These markings are remnants of the host rock within the turquoise, and can resemble splotches or veins. They’re called matrix.
Manufacturers try to fashion turquoise so that no matrix is visible, but sometimes it’s unavoidable. Small amounts of turquoise might be scattered through the host rock in such a way that the rough material can’t yield any cut specimens large enough to fashion into gems without including some matrix.
The presence of matrix can lower the value of turquoise, but that doesn’t mean turquoise with matrix is worthless or unmarketable. Some buyers actually prefer the presence of matrix in fashioned turquoise if its effect is attractive and balanced.
This is especially true if it’s a type of turquoise known in the trade as spiderweb turquoise. It contains matrix in thin, delicate, web-like patterns across the face of the gemstone. The patterns provide a dark contrast to the gem’s bright blue.
In the market for top-quality turquoise, stones with no matrix at all command the highest prices. Gems with attractive spiderweb matrix rank second in value.
BIRTHSTONES & ANNIVERSARIES
Turquoise is the traditional birthstone for the month of December and the gem of the 11th anniversary.
CHEMISTRY: CuAl6(PO4)4 (OH)8.5H2O
COLOR: Blue to green
REFRACTIVE INDEX: 1.610 to 1.650
BIREFRINGENCE: Not detectable
SPECIFIC GRAVITY: 2.76 (+0.14, -0.36)
MOHS HARDNESS: 5 to 6
WHY WE LOVE THIS GEMSTONE
The spiderweb of veins that appear in turquoise are matrix: evidence of the surrounding rock.
A legacy of turquoise appreciation spans the globe, from ancient Egypt to Mesoamerica to China.
Turquoise is colored by copper, which creates some of the most vivid blues and greens in gems.