How to identify Turquoise

To correctly identify Turquoise (Turquoise (CuAl6(PO4)4(OH)8·4H2O)), 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

   Sky-blue, robin's egg blue, greenish-blue, apple-green. The color is often uniform but can be mottled or veined with matrix material. The most prized color is an intense, uniform sky-blue.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

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

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically cryptocrystalline, massive, or nodular. Can be porous. Often found as veinlets or crusts.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Rarely forms distinct crystals; typically occurs as cryptocrystalline masses, reniform (kidney-shaped), botryoidal (grape-like), stalactitic, or as vein fillings and incrustations. Microscopic crystals are triclinic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect on {001} and good on {100}, 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

   Forms as a secondary mineral in arid or semi-arid regions, typically in highly altered volcanic rocks (especially porphyry copper deposits) or sedimentary rocks (sandstones, shales) that have been intruded by igneous rocks. It is found in the oxidized zones of copper deposits, where acidic groundwater interacts with aluminum-rich minerals and phosphate-bearing solutions.

Key Facts

Hardness

5-6 on the Mohs scale

Specific Gravity

2.60-2.90

Crystal System

Triclinic

Color

Sky-blue, robin's egg blue, greenish-blue, apple-green

Luster

Waxy to subvitreous, dull, earthy

Transparency

Opaque

Fracture

Conchoidal to uneven

Cleavage

Perfect on {001}, good on {100} (rarely observed)

Composition

Hydrous copper aluminum phosphate

Physical characteristics

• Crystal Habit: Cryptocrystalline masses, nodules, reniform, botryoidal, stalactitic, vein fillings, incrustations. Rarely as minute, distinct triclinic crystals.
• Cleavage Type: Perfect on {001}, good on {100}. Due to its cryptocrystalline nature, cleavage is seldom observed in hand specimens.
• Fracture Type: Conchoidal to uneven, sometimes splintery.
• Tenacity: Brittle
• Luster Type: Waxy to subvitreous, sometimes dull or earthy.

Explore Turquoise