How to identify Tourmalinated Quartz, Schorl in Quartz

To correctly identify Tourmalinated Quartz, Schorl in Quartz (Schorl (black tourmaline) in Quartz), 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

   Quartz matrix is typically colorless, white, or smoky gray. Schorl inclusions are opaque black.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz is vitreous (glassy). Schorl is vitreous to resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth to slightly rough, depending on the polish and the prominence of tourmaline crystals.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz typically forms hexagonal prisms with pyramidal terminations, though in massive form it can be anhedral. Schorl forms prismatic, often striated crystals, which can be acicular (needle-like) or columnar within the quartz.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz has no true cleavage, exhibiting conchoidal fracture. Schorl has very poor to indistinct cleavage parallel to the c-axis.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in granitic pegmatites, hydrothermal veins, and regionally metamorphosed rocks. It is often associated with other pegmatitic minerals like feldspar and mica.

Key Facts

Hardness

Quartz: 7 (Mohs); Schorl: 7-7.5 (Mohs). The aggregate will scratch steel.

Specific Gravity

Quartz: 2.65 g/cm³; Schorl: 3.06-3.26 g/cm³. The aggregate will have an intermediate specific gravity.

Crystal System

Quartz: Trigonal; Schorl: Trigonal.

Color

Colorless, white, or smoky quartz with opaque black schorl inclusions.

Luster

Vitreous (glassy).

Transparency

Quartz: Transparent to translucent; Schorl: Opaque.

Fracture

Conchoidal (for quartz); Uneven to conchoidal (for schorl).

Cleavage

None (for quartz); Very poor to indistinct (for schorl).

Composition

Quartz: SiO₂ (Silicon Dioxide); Schorl: NaFe₃Al₆(BO₃)₃Si₆O₁₈(OH)₄ (Sodium Iron Aluminum Borosilicate Hydroxide).

Physical characteristics

• Crystal Habit: Quartz: Massive, granular, or prismatic crystals. Schorl: Acicular, prismatic, columnar, or radiating aggregates within the quartz.
• Cleavage Type: Quartz: None; Schorl: Very poor to indistinct on {1011} and {1120}.
• Fracture Type: Quartz: Conchoidal; Schorl: Uneven to conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous (glassy).

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