Skip to Content


Home > Turquoise > Turquoise Story > Physical Properties of Turquoise CuAl6 [(OH)2/PO4]4

< Previous | Next >

Physical Properties of Turquoise CuAl6 [(OH)2/PO4]4

Most specimens are cryptocrystalline, meaning that the crystals can only be seen by a microscope In chemical terms, turquoise is a hydrated phosphate of copper and aluminum, and is formed as water trickles through a host stone for about 30 million years, gradually leaving a deposit. Turquoise is usually found in the "alteration zones" of arid or desert regions. These zones are areas where the native, original rocks have been altered through the intrusion of other rocks from some volcanic or other thermal influence. The hydrothermal alteration is created by magma solutions from deep in the earth being forced to the surface through fractures or pores which eventually change the original rocks.

Several steps and processes are necessary to create the unique properties of turquoise. First there must be a source of copper. This occurs in a rather limited number of areas in the world. There must be a source of phosphorus co-located with the copper, usually from the mineral Apatite, which is not always in rocks associated with copper.

There must also be feldspar for the aluminum, along with deep hydrothermal alteration, which breaks down the feldspars and frees the aluminum needed for the turquoise. The phosphorus usually comes from phosphoric acid leached from the Apatite, during the hydrothermal alteration.

The copper is usually introduced into the "host" rocks by the rising hot magma. The copper readily oxidizes near the surface when it is in the hot magma solution. It reacts freely with the aluminum and phosphoric acid to form turquoise. Another key geological activity is called silicafication; it too is an act of hydrothermal and intrusive alteration. Here silica, which is a common associate of turquoise, is introduced into the turquoise deposit. This addition combined with periods of intense heat are responsible for the hardness of the turquoise and frequently the matrix as well.

At this time other minerals enter into the turquoise structure and create color variations. The chemical formula of turquoise is: (CuAl6 (PO4)8 4H2O) this structure will vary greatly with the introduction of Iron, Calcium, Magnesium, Manganese, Silicon, and Zinc. These additional elements when incorporated in the molecular structure of turquoise influence its color and hardness. The color of turquoise can vary from a deep blue to a deep green, with every variation of color in-between. Generally, the more copper in the molecular structure the bluer the turquoise. The introduction of iron causes a greener cast to the stone.

To explain further, turquoise must consist of copper, aluminum and phosphorus. Other elements can replace various percentages of these and change the molecular structure. For example, two very rare minerals, Chalcasiderite (where iron replaces the aluminum, creating a yellow-green color), and Faustite (where zinc replaces the aluminum, creating a lime yellow-green color), do exist in turquoise environments. Usually there will only be a partial replacement of the aluminum with iron and zinc, thus leaving the turquoise properties altered only in color.

Turquoise is opaque and has a Mohs scale hardness that varies greatly. The deeply mined chalk-like turquoise may only have a mohs hardness slightly over 2, while a gem specimen mined closer to the surface may be up to 6. The hardness varies due to several factors, including both the environment and the matrix or host rock in which the turquoise is found.

In silica varieties of turquoise, quartz particles are present and the stone will be hard enough for use as a gem stone. Silicafication will strengthen some of the matrix as well. If some extent of silicification has not occurred, the turquoise properties will likely be chalky, porous, and soft. It will not be usable in jewelry without undergoing some form of treatment to harden or stabilize the stone. Stabilization may also be used because moisture will cause turquoise to turn toward green This can occur in the ground or in jewelry by absorbing moisture and oils. This is not unlike blue azurite changing to green malachite as its creation environment increases its water content.

Turquoise can be formed in many ways. It can appear as nuggets or it can be deposited in cracks in rocks, which then form vein turquoise. Turquoise can be formed in a cavity lined with quartz crystals and, most interesting, can take the place of another crystal when that crystal dissolves and become a "pseudo morph" or false form. This could give the impression that it is an actual turquoise crystal. Since turquoise is a mineral that is deposited by water solutions, turquoise can take the shape of cavities left when the stems and parts of fossil plants were dissolved out of harder rock or matrix, leaving turquoise in its place. Although this is sometimes referred to as "Fossil" turquoise, the term is incorrect, since "fossil" means the actual remains of plants or animals preserved in the rocks of the earth's crust.

If you believe, as Native Americans believe, that the earth is alive, then all things, no matter how small or apparently inanimate, are precious. To the Native American, Turquoise is Life. In the modern age, there is still this primal recognition of life-giving rock: the smooth stones that lie in streams, the clear quartz that juts from limestone, the humble stone found on a walk, the little black pebble lying mysteriously on the path to your door. There are stones medicine men keep in their sacred bundles because they possess powers of healing. There is the stone that comes to you in dreams and the magic ring you wear on your finger. These rocks and stones are alive and give forth energy to those who wear and hold them. Stones and crystals have unique attributes that support and heal us. The properties of Turquoise are especially known for positive healing energy, to aid in mental functions, communication and expression and as a protector...

Here in the United States, turquoise is synonymous with the Southwest. Native American jewelry featuring turquoise is found in the streets, plazas and in the middle of the desert. Turquoise jewelry is worn over plain dresses, velvet blouses, satin skirts, cowboy shirts and ceremonial costumes, Anglos as well as Pueblo and Navajo Indians wear turquoise necklaces, turquoise pendants, turquoise bracelets, belts and pins and as much as they can at one time. Elsewhere, turquoise may come and go with fashion. Here turquoise is more precious than gold, an enduring expression of Native American culture. It is the birthstone of December and signifies success. All pictures on this page are of untreated, beautiful, Natural Turquoise.

Turquoise, once a luxury intended only for the noble, is worn by every native of the Southwest as a sign of relative wealth. The rain gods and the kachinas wear it. The Earth Mother herself was once a little figure made of turquoise, before Talking God brought Changing Woman to life.

Today, turquoise can be found in many countries of the world, but high-grade turquoise is found mostly in China, Tibet, Persia and the Southwest.

The name is derived from "Turkish Stone" because it was brought to Europe through the ancient trade route, via Turkey. Pure blue is rare; with most stones either a blue-green hue or else containing matrix. Deposits are found in Iran, China, Australia, Israel and the southwest United States. The deposits in the Sinai were already worked out by 4000 BC. At that time turquoise was used for jewelry, amulets and the preparation of cosmetics by the Egyptians.

Considered precious by the Native Americans, turquoise evokes peace of the soul, as when we gaze at the immensity of the sky. By gazing at turquoise the same way, we eventually feel a peace that surpasses all analysis. Turquoise amplifies light blue and blue/green rays in the Divine Light spectrum. When handled or worn, turquoise often turns a darker green, which is said to be caused by the absorption of lotions and body oils.

< Previous | Next >

^Back to Top^