Turquoise

Turquoise has been used for jewelry and decoration for thousands of years. The turquoise on the right is typical turquoise, while the sample on the left has had the copper replaced by iron. Iron can also cause yellow turquoise. Turquoise is usually altered to improve either its color or hardness, as it is a porous mineral and easy to alter. Unaltered turquoise is hard to find.

Color: Sky-blue, blue-green, apple-green

Color of streak: White

Moh’s hardness: 5-6

Density: 2.31-2.84 grams/cubic centimeter

Cleavage: None

Fracture: Conchoidal, uneven

Crystal system: (Triclinic) seldom; grape-shaped aggregates

Chemical composition: CuAl6(PO4)4(OH)8•5(H2O); a copper containing basic aluminum phosphate

Transparency: Translucent, opaque

Refractive index: 1.610-1.650

Double refraction: +0.040

Dispersion: None

Pleochroism: Absent

Absorption spectrum: (460), 432, (422)

Fluorescence: Week, green-yellow, light blue