How to identify Schorl

To correctly identify Schorl (Black Tourmaline), 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 to brownish-black.

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 forms prismatic crystals, often with distinct vertical striations on crystal faces.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Elongated, often columnar or acicular crystals with a characteristic triangular cross-section (though often appearing hexagonal due to truncation). Terminations can be complex, often hemimorphic.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

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

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granitic pegmatites, high-temperature hydrothermal veins, greisens, and metamorphic rocks (schists, 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 brownish or bluish tint

Luster

Vitreous to resinous

Transparency

Opaque

Fracture

Conchoidal to uneven

Cleavage

Poor to indistinct (basal)

Composition

Complex borosilicate of aluminum, iron, and other elements

Physical characteristics

• Crystal Habit: Prismatic, columnar, acicular, often with vertical striations; massive, granular.
• Cleavage Type: Poor to indistinct on {1011} and {0001}.
• Fracture Type: Conchoidal to uneven.
• Tenacity: Brittle.
• Luster Type: Vitreous to resinous.

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