sedimentary
Pyrite in Shale
Iron Disulfide (FeS2) in Argillaceous Shale
Hardness: 6-6.5 (pyrite), 2-3 (shale); Color: Brass-yellow (metallics), dark gray (matrix); Luster: Metallic; Crystal Structure: Isometric (cubic/pyritohedron); Cleavage: Poor/indistinct.
- Hardness
- 6-6
- Color
- Brass-yellow (metallics), dark gray (matrix)
- Luster
- Metallic
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Physical properties
Hardness: 6-6.5 (pyrite), 2-3 (shale); Color: Brass-yellow (metallics), dark gray (matrix); Luster: Metallic; Crystal Structure: Isometric (cubic/pyritohedron); Cleavage: Poor/indistinct.
Formation & geological history
Formed in low-oxygen marine environments through the reduction of sulfates by bacteria, which then react with iron in the sediment to create pyrite during diagenesis. Typical of Paleozoic to Mesozoic eras.
Uses & applications
Pyrite is used for sulfur and sulfuric acid production, and occasionally as an ornamental stone. Shale is used in the manufacture of cement, brick, and as a source of fossil fuels via hydraulic fracturing.
Geological facts
Commonly known as 'Fool's Gold' due to its resemblance to precious metal, pyrite sparks when struck with steel. In shale, it often replaces ancient organic matter or forms as thin layers (veins).
Field identification & locations
Identify by the brassy metallic streak and sulfur smell when crushed. Commonly found in coal beds and sedimentary basins worldwide. For collectors, look for the contrast between the dark host rock and the shiny metallic inclusions.
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