How to identify Pyrite in matrix

To correctly identify Pyrite in matrix (Pyrite (FeS2) in a host rock), 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

   Brassy yellow to pale gold, often with a metallic sheen. The matrix color will vary depending on the host rock (e.g., grey for shale, white for quartz, black for carbonaceous material).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Metallic, bright and reflective.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Pyrite crystals are typically hard and brittle. The texture of the matrix will vary (e.g., fine-grained for shale, granular for granite, crystalline for quartz).

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cubic, pyritohedral (12-faced pentagonal dodecahedron), or octahedral crystals are common. Striations are often visible on cubic faces. Can also occur as massive, granular, or radiating aggregates. The matrix will show its characteristic rock texture.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to indistinct cleavage, typically parting along cubic planes. Pyrite fractures conchoidally to unevenly. The matrix will exhibit its own cleavage or fracture properties.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in a wide range of geological settings: igneous (hydrothermal veins, disseminated in intrusions), metamorphic (schists, gneisses), and sedimentary rocks (shales, limestones, coal seams). Often associated with other sulfide minerals, quartz, calcite, and various silicates.

Key Facts

Hardness

6-6.5 on Mohs scale

Specific Gravity

4.95-5.10

Crystal System

Isometric (Cubic)

Color

Pale brass-yellow, metallic

Luster

Metallic

Transparency

Opaque

Fracture

Conchoidal to uneven

Cleavage

Poor to indistinct on {001}

Composition

Iron disulfide (FeS2)

Physical characteristics

• Crystal Habit: Cubic, pyritohedral, octahedral, massive, granular, radiating
• Cleavage Type: Poor to indistinct
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Metallic

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