How to identify Black Tourmaline

To correctly identify Black Tourmaline (Schorl), 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

   Opaque black, sometimes with a very dark blue or brown tint.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to resinous, sometimes sub-metallic on fresh fracture surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically forms elongated, prismatic crystals. Can also be massive or granular.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal (trigonal) system, often forming long, slender to stout prismatic crystals with characteristic vertical striations parallel to the c-axis. Cross-sections are typically triangular with rounded edges.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to indistinct, exhibiting a conchoidal to uneven fracture rather than true cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granitic pegmatites, granites, aplites, high-temperature hydrothermal veins, and metamorphic rocks like schists and gneisses.

Key Facts

Hardness

7-7.5 (Mohs scale)

Specific Gravity

3.06-3.26 g/cm³

Crystal System

Trigonal

Color

Opaque black, sometimes with a very dark blue or brown tint

Luster

Vitreous to resinous

Transparency

Opaque

Fracture

Conchoidal to uneven

Cleavage

Poor to indistinct (no true cleavage)

Composition

Complex borosilicate of aluminum, iron, and other elements

Physical characteristics

• Crystal Habit: Prismatic, columnar, acicular, massive, granular. Crystals are typically elongated with vertical striations.
• Cleavage Type: None to very poor, parting may be observed along rhombohedral planes.
• Fracture Type: Conchoidal to uneven, brittle.
• Tenacity: Brittle
• Luster Type: Vitreous to resinous, sometimes sub-metallic.

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