How to identify Pyrite in matrix

To correctly identify Pyrite in matrix (FeS2 in rock matrix), 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 tarnished or iridescent surface. The matrix color will vary widely.

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 can be fine-grained, coarse-grained, massive, or foliated depending on the rock type.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cubic, octahedral, or pyritohedral crystals are common for pyrite. Striations are often visible on crystal faces. Pyrite 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

   Pyrite has very poor to indistinct cleavage, typically fracturing conchoidally. The cleavage of the matrix will depend on the host rock (e.g., perfect cleavage in mica, no cleavage in quartz).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Pyrite forms in a wide range of environments: hydrothermal veins, sedimentary rocks (especially black shales, coal, and evaporites), metamorphic rocks, and as an accessory mineral in some igneous rocks. It is indicative of reducing conditions.

Key Facts

Hardness

6-6.5 on Mohs scale (for pyrite)

Specific Gravity

4.95-5.10 g/cm³ (for pyrite)

Crystal System

Isometric (for pyrite)

Color

Brassy yellow, pale gold (for pyrite); matrix color varies

Luster

Metallic (for pyrite); matrix luster varies

Transparency

Opaque (for pyrite)

Fracture

Conchoidal to uneven (for pyrite)

Cleavage

Very poor to indistinct (for pyrite)

Composition

Iron disulfide (FeS2) for pyrite; matrix composition varies widely

Physical characteristics

• Crystal Habit: Cubic, octahedral, pyritohedral, massive, granular, radiating (for pyrite)
• Cleavage Type: Very poor to indistinct (for pyrite)
• Fracture Type: Conchoidal to uneven (for pyrite)
• Tenacity: Brittle (for pyrite)
• Luster Type: Metallic (for pyrite)

Explore Pyrite in matrix