The physical properties of turquoise are valuable for its identification. They are also valuable information for the care of turquoise jewelry. Important properties are summarized in the accompanying table.
Weathering can significantly alter the physical properties of turquoise. Weathered turquoise might still have a desirable color, but its hardness and durability are reduced. This turquoise cannot be cut into useful cabochons or beads. Weathered turquoise is often crushed and used to make “composite” or “reconstituted” turquoise described in the “Natural Turquoise and Turquoise Treatments” section on the next page.
| Physical Properties of Turquoise | |
| Chemical Classification | Phosphate |
| Color | Sky blue (the most desirable as a gemstone), blue, bluish green, green, yellowish green; often with brown, gray, or black matrix, as spider-webbing or background color. |
| Streak | Bluish white to greenish white |
| Luster | Waxy to subvitreous. Dull or chalky when weathered. |
| Diaphaneity | Opaque |
| Cleavage | Perfect, but rarely seen because of the small grain size of most specimens |
| Mohs Hardness | 5 to 6 (often lower because of porosity or exposure to weathering) |
| Specific Gravity | 2.5 to 2.9 (variable because of porosity and other minerals included as matrix) |
| Diagnostic Properties | Color, refractive index |
| Chemical Composition | CuAl6(PO4)4(OH)8·4H2O |
| Crystal System | Triclinic |
| Uses | Gemstone, small sculptures, decorative stone |