How to identify Pyrite in Quartz

To correctly identify Pyrite in Quartz (Pyrite (FeS2) in Quartz (SiO2)), 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

   Pyrite: Brassy yellow to golden. Quartz: Colorless, white, gray, or various other colors depending on impurities (e.g., amethyst, citrine, smoky quartz).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Pyrite: Metallic, bright. Quartz: Vitreous (glassy) to greasy.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Pyrite: Crystalline, often euhedral to subhedral crystals embedded in quartz. Quartz: Crystalline, massive, granular.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Pyrite: Commonly cubes, pyritohedrons (12-sided), octahedrons, or combinations thereof; also massive, granular, or radiating. Quartz: Hexagonal prisms terminated by rhombohedra; also massive, cryptocrystalline.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Pyrite: Indistinct to poor on {001}. Quartz: None.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, metamorphic rocks (e.g., schists, gneisses), sedimentary rocks (e.g., black shales, coal seams), and igneous rocks (e.g., granites, pegmatites).

Key Facts

Hardness

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

Specific Gravity

Pyrite: 4.95-5.10. Quartz: 2.65.

Crystal System

Pyrite: Isometric. Quartz: Trigonal.

Color

Pyrite: Pale brass-yellow. Quartz: Colorless, white, gray, purple, pink, brown, black.

Luster

Pyrite: Metallic. Quartz: Vitreous to greasy.

Transparency

Pyrite: Opaque. Quartz: Transparent to translucent.

Fracture

Pyrite: Uneven to conchoidal. Quartz: Conchoidal.

Cleavage

Pyrite: Indistinct to poor on {001}. Quartz: None.

Composition

Pyrite: Iron disulfide (FeS2). Quartz: Silicon dioxide (SiO2).

Physical characteristics

• Crystal Habit: Pyrite: Cubes, pyritohedrons, octahedrons, massive, granular, radiating. Quartz: Prismatic, massive, granular, cryptocrystalline.
• Cleavage Type: Pyrite: Indistinct to poor. Quartz: Absent.
• Fracture Type: Pyrite: Uneven to conchoidal. Quartz: Conchoidal.
• Tenacity: Pyrite: Brittle. Quartz: Brittle.
• Luster Type: Pyrite: Metallic. Quartz: Vitreous.

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