How to identify Pyrite in host rock

To correctly identify Pyrite in host rock (Pyrite (FeS2) in sedimentary or metamorphic 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

   Brass-yellow to pale brass-yellow, often with a tarnished or iridescent surface. The host rock 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 can be euhedral (well-formed cubes, pyritohedrons, octahedrons), subhedral, or anhedral (massive, granular, nodular). The texture of the host rock will vary (e.g., fine-grained shale, crystalline marble).

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Cubic, pyritohedral (12-faced pentagonal dodecahedron), or octahedral crystals are common. Striations on cube faces are characteristic. Can also be massive, reniform, or stalactitic. In sedimentary rocks, it often forms concretions or framboids (spherical aggregates of microcrystals).

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Poor to indistinct on {001}. Pyrite typically fractures conchoidally or unevenly rather than cleaving.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Sedimentary environments (e.g., black shales, coal seams, limestones, sandstones) under anoxic conditions, often associated with organic matter. Metamorphic environments (e.g., schists, gneisses, slates, marbles) where it forms during recrystallization or hydrothermal alteration. Hydrothermal veins in various rock types. Igneous rocks, though less common as a primary mineral, can host pyrite in hydrothermal alteration zones.

Key Facts

Hardness

6 to 6.5 on Mohs scale (harder than a steel knife)

Specific Gravity

4.95 to 5.03 g/cm³ (relatively heavy for a non-metallic mineral)

Crystal System

Isometric (cubic)

Color

Pale brass-yellow, golden metallic

Luster

Metallic, splendent

Transparency

Opaque

Fracture

Conchoidal to uneven

Cleavage

Poor to indistinct on {001}

Composition

Iron sulfide (FeS2)

Physical characteristics

• Crystal Habit: Cubic, pyritohedral, octahedral, massive, granular, reniform, stalactitic, framboidal, concretions. Cube faces often striated.
• Cleavage Type: Poor/Indistinct
• Fracture Type: Conchoidal to uneven
• Tenacity: Brittle
• Luster Type: Metallic

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