How to identify Pyrite with Magnetite

To correctly identify Pyrite with Magnetite (FeS2 (Pyrite) with Fe3O4 (Magnetite)), 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. Magnetite: Black to dark gray.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Pyrite: Metallic. Magnetite: Metallic to submetallic.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Pyrite: Crystalline, often euhedral to subhedral crystals. Magnetite: Granular, massive, or octahedral crystals.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Pyrite: Cubes, pyritohedrons, octahedrons, often striated. Magnetite: Octahedrons, dodecahedrons, granular masses.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Pyrite: Poor to indistinct on {001}. Magnetite: None (parting on {111} sometimes observed).

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Hydrothermal veins, skarns, banded iron formations, sedimentary rocks (e.g., black shales), metamorphic rocks, igneous intrusions.

Key Facts

Hardness

Pyrite: 6-6.5 (Mohs). Magnetite: 5.5-6.5 (Mohs).

Specific Gravity

Pyrite: 4.95-5.02. Magnetite: 5.17-5.18.

Crystal System

Pyrite: Isometric. Magnetite: Isometric.

Color

Pyrite: Brassy yellow. Magnetite: Black to dark gray.

Luster

Pyrite: Metallic. Magnetite: Metallic to submetallic.

Transparency

Opaque for both.

Fracture

Pyrite: Uneven to conchoidal. Magnetite: Uneven to subconchoidal.

Cleavage

Pyrite: Poor to indistinct on {001}. Magnetite: None (parting on {111} sometimes observed).

Composition

Pyrite: Iron disulfide (FeS2). Magnetite: Iron oxide (Fe3O4).

Physical characteristics

• Crystal Habit: Pyrite: Cubes, pyritohedrons, octahedrons, massive, granular. Magnetite: Octahedrons, dodecahedrons, granular, massive.
• Cleavage Type: Pyrite: Poor/Indistinct. Magnetite: None (parting).
• Fracture Type: Pyrite: Uneven to conchoidal. Magnetite: Uneven to subconchoidal.
• Tenacity: Pyrite: Brittle. Magnetite: Brittle.
• Luster Type: Pyrite: Metallic. Magnetite: Metallic to submetallic.

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