Turquoise
Color: Light blue, sky blue, pale green, blue-green, turquoise-blue, apple green, greenish-gray.
Luster: Sub-vitreous, resinous, waxy, dull, earthy.
Hardness: 5 – 6 (Mohs scale)
Specific Gravity: 2.6 – 2.8
Crystal System: Triclinic
Classification: Turquoise Group
Turquoise
Etymology & Historical Context:
The name is derived from the French words turques or turquois, meaning “Turkish.” Historically, the raw material—primarily sourced from the southern slopes of the Alamdari (Almirsah) mountains in Iran—reached Europe through Turkey. The term has been recognized in its current context since at least the early 17th century.
Mineralogical Classification & Research:
- Modern Definition: Turquoise and its group members were redefined by Ford and Tuggert (1998), who established turquoise as the terminal member of the group.
- Compositional Heterogeneity: Ford and Tuggert (1998) noted that most gem-quality materials labeled as “turquoise” are actually heterogeneous. They identified Planerite as the most common constituent in commercial-grade turquoise.
- Structural Relationships:
- Isostructural with: Calcosiderite and Planerite.
- Group Relations: Part of the Turquoise Group, including the Calcosiderite–Turquoise series and the Planerite–Turquoise series.
- Analogues: Copper analogue of Faustite.
Geological Occurrence:
Turquoise is a secondary mineral typically found within the potassic alteration zones of hydrothermal copper porphyry deposits. It commonly forms through the interaction of meteoric waters with aluminous igneous or sedimentary rocks, typically in arid environments (e.g., as vein fillers in volcanic rocks or within phosphate sediments).
