How to identify Schorl

To correctly identify Schorl (Na(Fe2+3)Al6(Si6O18)(BO3)3(OH)3(OH)), 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 surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Typically forms elongated, prismatic crystals with characteristic vertical striations on the prism faces. Can also be massive or granular.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Hexagonal-like (trigonal) prisms, often terminated by rhombohedral or pedial faces. Cross-sections are typically rounded triangular.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to indistinct basal cleavage, often appearing to lack cleavage. Fracture is more common.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Granitic pegmatites, high-temperature hydrothermal veins, greisens, and regionally metamorphosed schists and gneisses. Often found in association with quartz, feldspar, mica, and other tourmaline varieties.

Key Facts

Hardness

7-7.5 on the Mohs scale

Specific Gravity

3.18-3.22

Crystal System

Trigonal

Color

Opaque black

Luster

Vitreous to resinous

Transparency

Opaque

Fracture

Conchoidal to uneven

Cleavage

Poor to indistinct basal cleavage {0001}

Composition

Sodium Iron Aluminum Borosilicate Hydroxide

Physical characteristics

• Crystal Habit: Prismatic, columnar, acicular, massive, granular. Prism faces typically show strong vertical striations.
• Cleavage Type: Poor to indistinct basal cleavage, often appearing absent.
• Fracture Type: Conchoidal to uneven, brittle.
• Tenacity: Brittle
• Luster Type: Vitreous to resinous, sometimes sub-metallic.

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