sedimentary
Pyritic Shale
Carbonaceous Shale with Iron Pyrite (FeS2)
Hardness: 3-4 (matrix) to 6-6.5 (pyrite), Color: Black/dark grey with metallic brassy-yellow inclusions, Luster: Dull/earthy matrix with metallic inclusions, Crystal structure: Isometric (pyrite cubes or grains), Specific gravity: ~2.6-5.0
- Hardness
- 3-4 (matrix) to 6-6
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Physical properties
Hardness: 3-4 (matrix) to 6-6.5 (pyrite), Color: Black/dark grey with metallic brassy-yellow inclusions, Luster: Dull/earthy matrix with metallic inclusions, Crystal structure: Isometric (pyrite cubes or grains), Specific gravity: ~2.6-5.0
Formation & geological history
Formed in low-oxygen, organic-rich marine or lacustrine environments where sulfate-reducing bacteria react with iron and organic matter. Often associated with Devonian or Pennsylvanian age strata.
Uses & applications
Historically used for sulfuric acid production; scientifically important for understanding paleo-environments; used in educational collections and as a source for fossil hunting.
Geological facts
Also known as 'Fool\'s Gold' in shale. The pyrite specifically forms through the biological reduction of seawater sulfate. These rocks are often fossiliferous, containing well-preserved carbonized remains.
Field identification & locations
Identify by its dark fissile (layering) nature and the brassy metallic glint of the pyrite. Common in coal-bearing regions and ancient sea beds. Be wary of 'pyrite disease' where the sulfur reacts with humidity to decay the specimen.
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