Turquoise

Turquoise typically has a hardness of 5 to 6 on the Mohs scale. Its characteristic color ranges from sky blue to green, often with dark matrix veins (limonite or other iron oxides/shales). The luster is waxy to subvitreous, and it is usually opaque. Crystal structure is triclinic, though well-formed crystals are rare; it commonly occurs in massive, botryoidal, reniform, or stalactitic habits. Cleavage is poor, and its specific gravity is around 2.6-2.9.

Turquoise is a secondary mineral usually found in arid regions, forming as a result of the alteration of aluminum-rich igneous rocks, particularly volcanics, that contain disseminated copper sulfides. It forms near the surface, typically in fractures and cavities, as precipitation from downward-percolating waters. The copper provides the blue color, and iron can lead to greener hues. It is generally considered a relatively young mineral, forming in the Cenozoic era, though exact age depends on the specific deposit.

Turquoise has been highly prized as a gemstone and ornamental stone for thousands of years. It is widely used in jewelry (necklaces, rings, earrings, bracelets) and for carvings and inlays. Due to its attractive color and cultural significance in many societies, it also holds value for collectors. It has limited industrial use.

Turquoise is one of the oldest known gemstones, used by ancient Egyptians, Persians, Native Americans, and other cultures. The name 'turquoise' comes from the French expression 'pierre turquoise' meaning 'Turkish stone,' likely because it first arrived in Europe from Persia through Turkey. Some of the most valuable turquoise comes from Iran (Persian Turquoise) and the American Southwest, particularly Arizona and Nevada. It is often treated or stabilized to enhance its color and durability.

In the field, turquoise can be identified by its distinctive blue-to-green color, often with brown or black matrix. Its relative softness (scratchable with a knife, but harder than common calcite) and waxy luster are also good indicators. It is found in dry, barren regions, typically in association with limonite, kaolinite, and other copper minerals. Major deposits are found in Iran, the Sinai Peninsula (Egypt), China, and the southwestern United States (Arizona, Nevada, New Mexico, Colorado). Look for it in weathered zones of copper-rich hydrothermal deposits.