How to identify Turquoise

To correctly identify Turquoise (CuAl6(PO4)4(OH)8 H2O), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Ranges from sky-blue to greenish-blue, apple-green, and yellowish-green. The most prized color is an intense, uniform sky-blue. Greenish hues are often due to iron impurities or dehydration.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Waxy to subvitreous, sometimes dull in lower quality or weathered specimens.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically massive, cryptocrystalline, or nodular. Can be porous. Often exhibits a fine-grained, compact texture.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Rarely forms distinct crystals; when it does, they are usually minute triclinic prisms. Most commonly found as botryoidal, reniform, stalactitic, or encrusting masses, or as vein fillings.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect on {001} and good on {010}, but rarely observed due to its cryptocrystalline nature. Fracture is typically conchoidal to uneven.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in arid regions as a secondary mineral in altered volcanic or sedimentary rocks, particularly those associated with copper deposits. It forms in the oxidation zone of copper sulfide deposits, where acidic waters react with aluminum-rich minerals and phosphates.

Key Facts

Hardness

5-6 on the Mohs scale

Specific Gravity

2.60-2.90 (typically 2.76)

Crystal System

Triclinic

Color

Blue, greenish-blue, green, yellowish-green

Luster

Waxy, subvitreous, dull

Transparency

Opaque, rarely semi-translucent in thin sections

Fracture

Conchoidal to uneven

Cleavage

Perfect on {001}, good on {010}, but rarely observed due to cryptocrystalline nature

Composition

Hydrous copper aluminum phosphate

Physical characteristics

• Crystal Habit: Cryptocrystalline masses, nodules, vein fillings, botryoidal, reniform, stalactitic, encrusting. Rarely as minute, tabular triclinic crystals.
• Cleavage Type: Perfect {001}, good {010} (rarely seen)
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Waxy to subvitreous

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