How to identify Crushed aggregate with pyrite

To correctly identify Crushed aggregate with pyrite (Mixed rock fragments with Pyrite (FeS2)), 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

   The aggregate itself will have the color of its constituent rock fragments (e.g., grey, brown, red, white). Pyrite within the aggregate will appear as brassy yellow, metallic specks or crystals.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   The rock fragments will have variable luster (e.g., dull, earthy, vitreous). Pyrite will exhibit a distinct metallic luster.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Angular to sub-angular fragments, typically ranging from sand to gravel size. Pyrite may be disseminated as fine grains, larger crystals, or nodular masses within the rock fragments.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Pyrite often forms cubic, pyritohedral, or octahedral crystals, or can be massive, granular, or radiating. In aggregate, these forms may be fractured.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Pyrite has indistinct cleavage, typically exhibiting conchoidal or uneven fracture. The cleavage of the host rock fragments will vary.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Pyrite-bearing rocks are found in diverse environments: sedimentary rocks (shales, coals, limestones), hydrothermal veins, metamorphic rocks, and some igneous rocks. The aggregate is sourced from quarries or mines extracting these rock types.

Key Facts

Hardness

6-6.5 on Mohs scale (for pyrite), variable for host rock

Specific Gravity

4.95-5.03 (for pyrite), variable for host rock

Crystal System

Isometric (for pyrite), variable for host rock

Color

Pale brass-yellow (for pyrite), variable for host rock

Luster

Metallic (for pyrite), variable for host rock

Transparency

Opaque (for pyrite), variable for host rock

Fracture

Conchoidal to uneven (for pyrite), variable for host rock

Cleavage

Indistinct (for pyrite), variable for host rock

Composition

Iron disulfide (FeS2) within various silicate or carbonate rock fragments

Physical characteristics

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

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