TURQUOISE

GEMOLOGICAL PROPERTIES OF TURQUOISE

Chemical Composition:

Turquoise is a hydrous phosphate of copper and aluminum. Its chemical formula is (CuAl6(PO4)4(OH)8·4H2O). The blue color is attributed to copper, while the greenish hues come from iron.

Color:

Turquoise is famous for its blue to greenish-blue color. The most valuable turquoise often has an even, intense blue color with minimal matrix (vein-like patterns or host rock inclusions).

Matrix:

Turquoise is sometimes found with a matrix, which is the host rock in which the turquoise forms. The presence and appearance of the matrix can affect the overall aesthetics of the stone.

Stabilization:

Turquoise is commonly stabilized to enhance its durability and color. Stabilization involves impregnating the stone with a clear resin, wax, or other substances to reduce porosity and prevent color changes over time.

Cut:

Turquoise is cut into various shapes, including cabochons, beads, and carvings. The cut is chosen to maximize the stone’s color and minimize any visible inclusions.

Hardness:

Turquoise has a hardness ranging from 5 to 6 on the Mohs scale. While it is suitable for jewelry, care should be taken to avoid scratching.

Luster:

Turquoise exhibits a waxy to subvitreous luster, giving it a smooth and somewhat shiny appearance.

Transparency:

Turquoise is typically opaque, but some higher-grade specimens may exhibit slight translucency.

Specific Gravity:

The specific gravity of turquoise ranges from 2.60 to 2.85.

Cleavage:

Turquoise has no cleavage, which means it does not break along specific planes.

Reactivity:

Turquoise can be sensitive to chemicals, heat, and prolonged exposure to sunlight. It is advised to avoid exposing turquoise jewelry to harsh chemicals and high temperatures.

Origin:

Turquoise is found in various locations globally, including the United States (Southwestern regions like Arizona and New Mexico), Iran, China, Mexico, and Egypt. The origin can influence the color and specific features of the stone.

Treatments: Besides stabilization, turquoise may undergo other treatments, such as dyeing or impregnation with polymers, to enhance color or fill fractures. These treatments should be disclosed by sellers.

Imitations:

Due to its popularity, turquoise is sometimes imitated using various materials, including dyed howlite or magnesite. Gemological testing can help distinguish genuine turquoise from imitations.

Understanding these gemological properties is essential for gemologists and buyers when assessing the quality and authenticity of turquoise gemstones.