Turquoise is one of the most important gemstones in the world, with a fascinating history going back almost 7500 years. This sky blue stone is thought to have first been discovered in Egypt and has since adorned the likes of Pharaohs and kings over the millennia. Valued not only for its beauty, but for its supernatural properties as well. It has been used by healers in many cultures around the world.
Turquoise formation is a rare occurrence around the world. It formed millions of years ago in arid climates such as Egypt or in the Southwest United States. Turquoise is a chemical mixture of copper and aluminum phosphates that forms through a process of hydro-thermal replacement. In other words, chemicals and minerals from nearby rocks are leached out by rain or other water and reformed in the crevices of other hosts, commonly rhyolite, limestone, quartz or chert. These other host minerals make up the stone’s matrix.
There are a lot of terms that get thrown around in the turquoise world. Natural, stabilized, treated, enhanced, reconstituted, block, and chalk are all used to describe the various types and qualities of turquoise.
Natural, gem quality turquoise is the most rare, and therefore most highly valued and desired type of turquoise. The term natural is used to describe turquoise which has been pulled from the ground and is hard enough to cut and polish without the need for any type of treatment. Estimates vary, but approximately only 30% of what is mined is hard enough to cut and polish in its natural state. Only around 3% of all turquoise mined is considered gem grade material.
Stabilized turquoise is the most common type of turquoise found on the market today. As most turquoise that is mined is unusable in its natural state, stabilizing adds a tremendous amount of value to otherwise worthless material. The process of stabilization involves injecting lower grade turquoise with epoxy under heat and pressure. This process not only hardens the stone, but it deepens the color as well. Stabilized turquoise is most commonly used in making beads and inlay jewelry. Stabilizing works with turquoise of all grades, from chalk and above.
Enhanced turquoise is natural turquoise that has undergone an electro-chemical process known as the Zachery method. Natural turquoise is placed in a bath of minerals that are naturally found in turquoise and an electrical current is then passed through the solution. This process reduces the porosity, deepens the natural color, and hardens the stone without introducing any unnatural elements like epoxy. In fact, typical lab tests will not show any treatment in Zachery treated turquoise other than a high level of potassium. Only mid to high grade turquoise rough can be treated using the Zachery method. It will not work on low grade chalk or material that crumbles too easily.
Chalk turquoise is low grade natural turquoise that is too soft to be cut and cut and polished in its natural state. It must be stabilized for use in jewelry.
Reconstituted turquoise is created by mixing crushed turquoise with epoxy and sometimes dye. Artists may use reconstituted turquoise to create very inexpensive jewelry, particularly heist necklaces. Reconstitution allows smaller pieces of turquoise to recombined into larger chunks which are useful in a variety of ways.
Block turquoise is created using only epoxy, dye and perhaps something like sand to create an artificial matrix. It is turquoise in color only.
Natural vs Treated
Collectors of turquoise often have deep rooted opinions regarding treatments. Some collectors avoid treated turquoise altogether, opting instead to buy only natural turquoise. Compared to stabilized or enhanced material, natural turquoise will usually be considered more valuable. However, the term natural should not be confused with gem grade turquoise. Much of the natural turquoise on the market is still a mid grade at best and would actually benefit greatly from being treated. Stabilized or enhanced turquoise can often be much prettier than natural turquoise, and in those cases can also be much more valuable. Natural turquoise also has a tendency to absorb skin oils over time which will eventually change the color of the stone. Much of the natural turquoise set in jewelry during the turquoise boom of the 1970s has turned from blue to green. Though in countries like China, this color change is actually desired as the turquoise “ages” with its wearer.
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