How to identify Tourmaline

To correctly identify Tourmaline (Tourmaline Group), 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

   Extremely variable; black (Schorl), pink to red (Rubellite), blue (Indicolite), green (Verdelite), yellow, brown (Dravite), colorless (Achroite), bi-colored, tri-colored (Watermelon Tourmaline).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically prismatic crystals, often with a triangular cross-section and prominent vertical striations.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Elongated prismatic crystals, often terminated by rhombohedral or pedion faces. Cross-sections are typically rounded triangular.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to indistinct, often appearing absent. Fracture is conchoidal to uneven.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granitic pegmatites, high-temperature hydrothermal veins, greisens, metamorphic schists, gneisses, and quartzites. Also found in detrital sediments.

Key Facts

Hardness

7-7.5 on the Mohs scale

Specific Gravity

2.90-3.26 (varies with composition)

Crystal System

Trigonal

Color

Extremely variable (black, pink, green, blue, brown, colorless, multi-colored)

Luster

Vitreous to resinous

Transparency

Transparent to opaque

Fracture

Conchoidal to uneven

Cleavage

Poor to indistinct (often appears absent)

Composition

Complex borosilicate, (Na,Ca)(Li,Mg,Fe,Mn,Al)3Al6(BO3)3Si6O18(OH,F)4. The general formula is XY3Z6(T6O18)(BO3)3V3W, where X, Y, Z, T, V, W represent various cation and anion sites.

Physical characteristics

• Crystal Habit: Prismatic, often elongated, with vertical striations on prism faces; typically terminated by rhombohedral or pedion faces. Cross-section often rounded triangular.
• Cleavage Type: Poor to indistinct, typically not observed.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous to resinous.

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