How to identify Quartz with Tourmaline and Pyrite

To correctly identify Quartz with Tourmaline and Pyrite (Quartz (SiO2), Tourmaline (complex borosilicate), 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

   Quartz: Colorless, white, milky, smoky, purple (amethyst), yellow (citrine). Tourmaline: Typically black (schorl), but can be green, pink, blue, or multi-colored. Pyrite: Opaque, metallic brass-yellow.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Quartz: Vitreous (glassy). Tourmaline: Vitreous to resinous. Pyrite: Metallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Crystalline, often with distinct crystal forms of each mineral. Quartz can be massive or euhedral. Tourmaline typically prismatic. Pyrite often cubic or octahedral.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Quartz: Hexagonal prisms terminated by rhombohedra. Tourmaline: Elongated prismatic crystals with characteristic rounded triangular cross-section and vertical striations. Pyrite: Cubic, octahedral, or pyritohedral crystals, often striated.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Quartz: None (conchoidal fracture). Tourmaline: Poor basal cleavage, often not observed. Pyrite: Indistinct to poor cleavage on {001} and {110}.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, pegmatites, greisens, and metamorphic rocks. Often found in association with granitic intrusions.

Key Facts

Hardness

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

Specific Gravity

Quartz: 2.65 g/cm³. Tourmaline: 3.0-3.26 g/cm³. Pyrite: 4.95-5.10 g/cm³.

Crystal System

Quartz: Trigonal. Tourmaline: Trigonal. Pyrite: Isometric.

Color

As described above, highly variable depending on the specific mineral.

Luster

As described above, vitreous for quartz and tourmaline, metallic for pyrite.

Transparency

Quartz: Transparent to translucent. Tourmaline: Transparent to opaque. Pyrite: Opaque.

Fracture

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

Cleavage

Quartz: None. Tourmaline: Poor basal. Pyrite: Indistinct to poor.

Composition

Quartz: Silicon dioxide (SiO2). Tourmaline: Complex borosilicate, general formula XY3Z6(T6O18)(BO3)3V3W (where X, Y, Z, T, V, W are various cations and anions). Pyrite: Iron disulfide (FeS2).

Physical characteristics

• Crystal Habit: Quartz: Prismatic, massive. Tourmaline: Prismatic, acicular, massive. Pyrite: Cubic, octahedral, pyritohedral, massive.
• Cleavage Type: Quartz: None. Tourmaline: Poor/indistinct. Pyrite: Indistinct to poor.
• Fracture Type: Quartz: Conchoidal. Tourmaline: Uneven to conchoidal. Pyrite: Conchoidal to uneven.
• Tenacity: Quartz: Brittle. Tourmaline: Brittle. Pyrite: Brittle.
• Luster Type: Quartz: Vitreous. Tourmaline: Vitreous to resinous. Pyrite: Metallic.

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