How to identify Tourmaline

To correctly identify Tourmaline (Complex borosilicate mineral 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, including black (schorl), pink to red (rubellite), blue (indicolite), green (verdelite), yellow, brown (dravite), colorless (achroite), and multi-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 smooth on crystal faces, but can be rough if etched or weathered.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Prismatic crystals, often elongated, with characteristic rounded triangular cross-sections. Vertical striations are common on prism faces. Can also be massive or columnar.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Indistinct to poor, often appearing as conchoidal fracture rather than true cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granitic pegmatites, aplites, hydrothermal veins, metamorphic schists, gneisses, and quartzites. Also found in detrital sediments due to its resistance to weathering.

Key Facts

Hardness

7-7.5 on the Mohs scale

Specific Gravity

2.9-3.2 (varies with composition)

Crystal System

Trigonal

Color

Extremely variable, often pleochroic

Luster

Vitreous to resinous

Transparency

Transparent to opaque

Fracture

Conchoidal to uneven

Cleavage

Indistinct to poor (often appears as fracture)

Composition

Complex borosilicate of aluminum, iron, magnesium, sodium, lithium, and other elements

Physical characteristics

• Crystal Habit: Prismatic, columnar, acicular, massive, compact. Crystals often show a characteristic rounded triangular cross-section and vertical striations.
• Cleavage Type: Indistinct to poor, basal {0001} and rhombohedral {1011}. Fracture is more common than cleavage.
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Vitreous to resinous

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