How to identify Pyrite in matrix

To correctly identify Pyrite in matrix (Pyrite (FeS2) in 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 golden metallic for pyrite; matrix color varies widely (e.g., white for quartz, black for shale, gray for slate).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Metallic for pyrite; matrix luster varies (e.g., vitreous for quartz, dull for shale, silky for some metamorphic rocks).

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Pyrite crystals are typically hard and angular, often with striations on crystal faces. The texture of the matrix depends on its rock type (e.g., granular for sandstone, foliated for schist, massive for granite).

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Pyrite commonly forms cubes, octahedra, or pyritohedra, often with striated faces. It 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 indistinct cleavage, typically conchoidal to uneven fracture. The cleavage of the matrix depends on its mineral composition (e.g., perfect cleavage in mica-rich schists, no cleavage in quartz).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in a wide range of geological settings: hydrothermal veins, sedimentary rocks (especially black shales and coal seams), metamorphic rocks, and as an accessory mineral in some igneous rocks. The specific environment dictates the nature of the matrix.

Key Facts

Hardness

6-6.5 on Mohs scale

Specific Gravity

4.95-5.10

Crystal System

Isometric (cubic)

Color

Pale brass-yellow, golden metallic

Luster

Metallic

Transparency

Opaque

Fracture

Conchoidal to uneven

Cleavage

Indistinct on {100} and {111}

Composition

Iron disulfide (FeS2)

Physical characteristics

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

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