Shale with Pyrite

Physical Properties

Hardness: 3-4 (rock matrix); Color: Dark gray to black with brassy yellow metallic inclusions; Luster: Dull (matrix) to Metallic (pyrite inclusions); Structure: Fissile, fine-grained bedding; Cleavage: No true cleavage in matrix, pyrite shows uneven fracture.

Formation & Geological History

Formed through the accumulation of silt and clay-sized mineral particles in quiet water environments like deep lakes or sea floors under anaerobic conditions, facilitating the growth of sulfide minerals (pyrite).

Uses & Applications

Used primarily in the manufacture of cement and as a source of sulfur for sulfuric acid in some contexts; pyrite crystals are popular among collectors.

Geological Facts

Pyrite is often called 'Fool's Gold' because of its metallic luster and yellow hue. When found in shale, it often indicates the presence of organic matter and low-oxygen formation environments.

Field Identification & Locations

Identify by its thin, flat layers (laminae) that split easily and the presence of metallic 'flecks' or 'cubes' within the gray-black matrix. Commonly found in riverbeds and outcrop cliffs.

Identified on: 5/18/2026

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