How to identify Tourmaline in Quartz with Pyrite

To correctly identify Tourmaline in Quartz with Pyrite (Schorl (black tourmaline) in Quartz (SiO2) with Pyrite (FeS2)), 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

   Black (schorl), colorless to white/milky/smoky (quartz), brassy yellow (pyrite).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (quartz), sub-vitreous to resinous (schorl), metallic (pyrite).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Crystalline, often with distinct euhedral to subhedral crystals of tourmaline and pyrite within a granular or massive quartz matrix.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Schorl: Prismatic, typically elongated, often with characteristic triangular cross-sections and vertical striations. Quartz: Hexagonal prisms terminating in rhombohedra, or massive/anhedral. Pyrite: Cubes, octahedra, pyritohedra, or massive.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Schorl: Indistinct to poor prismatic cleavage. Pyrite: Indistinct to poor cubic cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, pegmatites, greisens, and contact metamorphic zones associated with granitic intrusions. Often found in areas of significant tectonic activity and fluid flow.

Key Facts

Hardness

Quartz: 7 (Mohs). Schorl: 7-7.5 (Mohs). Pyrite: 6-6.5 (Mohs).

Specific Gravity

Quartz: 2.65. Schorl: 3.1-3.2. Pyrite: 4.95-5.10.

Crystal System

Quartz: Trigonal. Schorl: Trigonal. Pyrite: Isometric.

Color

Black (schorl), colorless to white/milky/smoky (quartz), brassy yellow (pyrite).

Luster

Vitreous (quartz), sub-vitreous to resinous (schorl), metallic (pyrite).

Transparency

Quartz: Transparent to translucent. Schorl: Opaque. Pyrite: Opaque.

Fracture

Quartz: Conchoidal. Schorl: Uneven to conchoidal. Pyrite: Conchoidal to uneven.

Cleavage

Quartz: None. Schorl: Indistinct to poor prismatic. Pyrite: Indistinct to poor cubic.

Composition

Quartz: Silicon dioxide (SiO_2). Schorl: Sodium iron aluminum borosilicate hydroxide (Na(Fe2+)_3Al_6(BO_3)_3Si_6O_18(OH)_4). Pyrite: Iron disulfide (FeS_2).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive, granular. Schorl: Prismatic, acicular, massive. Pyrite: Cubic, octahedral, pyritohedral, massive.
• Cleavage Type: Quartz: Absent. Schorl: Poor prismatic. Pyrite: Poor cubic.
• Fracture Type: Quartz: Conchoidal. Schorl: Uneven to conchoidal. Pyrite: Conchoidal to uneven.
• Tenacity: Quartz: Brittle. Schorl: Brittle. Pyrite: Brittle.
• Luster Type: Quartz: Vitreous. Schorl: Sub-vitreous to resinous. Pyrite: Metallic.

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