Turquoise

Hardness: 5-6 on Mohs scale. Color: Blue, bluish-green, green. Luster: Waxy to subvitreous. Crystal structure: Triclinic, typically opaque massive, nodular or reniform habits, rarely as small crystals. Cleavage: Good to distinct on {001}. Specific Gravity: 2.6-2.9.

Turquoise forms as a secondary mineral in arid regions, primarily in weathered igneous rocks (especially those rich in aluminum) that contain copper minerals. It precipitates from circulating groundwater that carries copper, aluminum, and phosphorus. Its formation is typically associated with hydrothermal processes and the alteration of pre-existing minerals. Geological age can vary, but many significant deposits are relatively young, forming in the Cenozoic era.

Turquoise has been highly prized as a gemstone for thousands of years, used extensively in jewelry, ornamental carvings, and as a decorative stone. It is often cut into cabochons, beads (as seen in the image), and inlays. Its distinctive color makes it popular in Native American jewelry, particularly from the Southwestern United States. It has spiritual and cultural significance in many societies.

The name 'turquoise' dates from the 17th century and is derived from 'French turquois', meaning 'Turkish', because the gem was first brought to Europe from Turkey, through which it arrived from Persia (modern-day Iran) and Afghanistan. Ancient Egyptians and Mesoamerican cultures treasured turquoise. It's one of the birthstones for December.

In the field, turquoise is identified by its characteristic blue to green color, waxy luster, and its occurrence in arid regions, often in veins or nodules within altered host rocks. It can be distinguished from similar-looking minerals like amazonite or chrysocolla by its slightly lower hardness and specific gravity. The presence of 'matrix' (remnants of the host rock, often dark brown or black) is a common identifying feature. Major deposits are found in Iran (formerly Persia), the Southwestern United States (Arizona, Nevada, New Mexico), China, Egypt, Mexico, and Chile. Collectors look for vibrant, uniform color and the presence of interesting matrix patterns.