sedimentary
Pyrite Concretion
Iron Sulfide (FeS2) in Sedimentary Matrix
Hardness: 6-6.5 (for the pyrite crystals); Color: Brassy yellow crystals on earthy brown matrix; Luster: Metallic (crystals) to dull (matrix); Crystal structure: Isometric (cubic or pyritohedral crystals)
- Hardness
- 6-6
- Color
- Brassy yellow crystals on earthy brown matrix
- Luster
- Metallic (crystals) to dull (matrix)
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Physical properties
Hardness: 6-6.5 (for the pyrite crystals); Color: Brassy yellow crystals on earthy brown matrix; Luster: Metallic (crystals) to dull (matrix); Crystal structure: Isometric (cubic or pyritohedral crystals)
Formation & geological history
Formed in anaerobic (oxygen-poor) sedimentary environments, often in shales or mudstones, where organic matter decays and reacts with iron and sulfur in the groundwater to precipitate crystals around a nucleus.
Uses & applications
Primarily collected as geological specimens; historically used to create sparks for starting fires and in the production of sulfuric acid.
Geological facts
Pyrite is famously known as 'Fool's Gold' due to its metallic luster and brassy hue. Concretions like this often form in perfect spheres or discs depending on the surrounding pressure during formation.
Field identification & locations
Identify in the field by looking for metallic, cubic crystal growths protruding from a softer, rounded sedimentary rock. Commonly found in coal beds and marine shale deposits.
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