Turquoise
Cyan sky, reddish blue: Vivid shades of turquoise define the color that is named after this gemstone.
Turquoise is found in only a few places on Earth: in arid and barren areas, where acidic groundwater rich in copper seeps downwards and reacts with minerals that contain phosphorus and aluminum. The result of this sedimentation process is a porous, semi-transparent to opaque compound of hydrated copper and aluminum phosphate.
Turquoise is a prime example of an opaque colored stone that can be sold as a jewelry gem and as a decorative material.
Turquoise may lack the sparkle and clarity of transparent colored gemstones such as ruby, emerald and sapphire, but its multi-layered history and soul-satisfying color make it a sought-after gemstone. Its color can range from matte green through grass to light, medium toned, sky blue. People highly value turquoise for its combination of ancient heritage and unforgettable color.
The traditional source of the highest color, sometimes referred to as blush blue or sky blue, is Nishapur District in Iran, a country formerly known as Persia. So quite often you hear people in the store call the turquoise of this beautiful color “Persian blue”, whether or not it was actually mined in Iran.
Top turquoise has inspired designers to create elegant jewelry. It is most often cut into cabochons, but it can also be cut into balls or flat pieces for unloading.
Although many turquoise jewelry is elegant and modern, many consumers in the United States are familiar with traditional Indian jewelry such as Pueblo, Hopi, Zuni and Navajo. People who are interested in Native American arts and crafts often collect these stylized silver jewelry.
Turquoise is relatively soft, so it is ideal for carving. Artists in Europe, Asia, the Middle East and America choose turquoise as a medium for carved jewelry and art objects. It is often used to make talismans of Native American importance, such as carved birds and animals called fetishes.
Turquoise owes its texture to its structure and composition. It is a collection of microscopic crystals that form a solid. If the crystals are packed close together, the material is less porous, so it has a finer structure. Turquoise with a fine texture has an attractive wax luster after polishing. Turquoise with a less dense crystal structure has a higher porosity and a coarser texture, which results in a matte gloss when polished.
Porosity and texture not only affect appearance: they also affect durability. Turquoise is relatively soft – on the Mohs scale it is 5 to 6. Turquoise with a rough texture can also have weak toughness. Samples with a finer texture have adequate 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 be smoother, shinier and more marketable.
Turquoise deposits usually form in limonite or iron-rich sandstone. Limonite produces dark brown characters in turquoise, while sandstone produces light brown characters. These marks are remnants of the host rock in turquoise and may resemble spots or veins. They are called matrices.
Manufacturers try to shape the turquoise so that the matrix is not visible, but sometimes this cannot be avoided. Small amounts of turquoise can be dispersed across the host rock in such a way that the coarse material cannot provide any cut samples large enough to produce gemstones without the inclusion of any matrix.
The presence of a matrix can reduce the value of turquoise, but this does not mean that turquoise with a matrix is worthless or unsaleable. Some buyers actually prefer the presence of a matrix in fashionable turquoise if its effect is attractive and balanced.
This is especially true when it comes to the type of turquoise known in the store as cobweb turquoise. It contains a matrix in thin, fine, reticulated patterns over the entire surface of the gemstone. The patterns provide a dark contrast to the bright blue color of the gemstone.
In the market with the highest quality turquoise, the highest prices are achieved by non-matrix stones. Gems with an attractive cobweb matrix are in second place in value.
