mineral

Pyrite in Shale

Iron Disulfide (FeS2) in Sedimentary Shale

Pyrite: Hardness 6-6.5, brass-yellow color, metallic luster, isometric/cubic crystal system, greenish-black streak. Shale: Soft (approx. 3), grey-to-black, fine-grained, fissile (layers).

Identified February 25, 2026More mineral →

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Physical properties

Pyrite: Hardness 6-6.5, brass-yellow color, metallic luster, isometric/cubic crystal system, greenish-black streak. Shale: Soft (approx. 3), grey-to-black, fine-grained, fissile (layers).

Formation & geological history

Formed in an oxygen-poor (anoxic) marine environment where organic matter and bacteria reacted with iron-rich sediments to precipitate sulfide minerals. This specimen likely dates from the Paleozoic or Mesozoic eras.

Uses & applications

Major source of sulfur; historical source for sulfuric acid. High-quality cubic specimens are popular for mineral collectors and jewelry. Shale is used in cement production and as a source for natural gas.

Geological facts

Known as 'Fool's Gold' due to its resemblance to real gold, though it is much harder and leaves a black streak rather than yellow. Pyrites found in shale often form 'nodules' or 'sun' shapes.

Field identification & locations

Identify by its metallic brassy sheen against the matte grey of the surrounding shale. Common in coal beds and sedimentary cliff faces globally; frequently found in the Ohio and Mississippi River Valleys.

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