How to identify Pyrite in Quartz

To correctly identify Pyrite in Quartz (FeS2 in 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, metallic. Quartz: Colorless, white, gray, or smoky, often translucent to transparent.

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: Massive, granular, or crystalline.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Pyrite: Commonly cubic, pyritohedral, or octahedral crystals, sometimes striated. Quartz: Hexagonal prisms with rhombohedral terminations, massive, or cryptocrystalline.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Pyrite: Indistinct to poor on {001}. Quartz: None (conchoidal fracture).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, metamorphic rocks, sedimentary rocks (especially black shales), and igneous rocks. Often associated with ore deposits of gold, copper, and other metals.

Key Facts

Hardness

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

Specific Gravity

Pyrite: 4.95-5.02; Quartz: 2.65.

Crystal System

Pyrite: Isometric; Quartz: Trigonal.

Color

Pyrite: Brassy yellow; Quartz: Colorless, white, gray, smoky.

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, often striated. Quartz: Prismatic, massive, granular.
• Cleavage Type: Pyrite: Indistinct/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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