mineral

Pyrite nodule (probable iron sulfide concretion)

Pyrite, FeS₂, likely weathered within a sedimentary concretion

AI-generated identification · may be incorrect

The rounded, tan weathered outer shell and dark metallic-looking interior suggest a pyrite-bearing nodule. Pyrite has Mohs hardness 6–6.5, pale brass-yellow color, metallic luster, cubic crystals when developed, and no prominent cleavage; the specimen appears heavily oxidized and lacks obvious crystal faces.

Identified August 22, 2026More mineral →

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Physical properties

Formation & geological history

Likely formed when pyrite precipitated in muddy sediment and became enclosed in a concretion, commonly during diagenesis in sedimentary rocks. Its precise geological age and locality cannot be determined from the photograph.

Uses & applications

Pyrite is collected for its metallic appearance, educational use, and sometimes mineral displays; it is not generally used as jewelry when weathered because oxidation can produce acidic products. Pyrite-bearing nodules may also be associated with coal and sulfide ore deposits.

Geological facts

Fresh pyrite is brass-yellow and may produce a dark streak, unlike gold’s yellow streak and softness. Weathering commonly converts it to iron oxides, giving the rusty tan-brown crust visible here.

Field identification & locations

Look for a heavy specimen, metallic brass-yellow surfaces, cubic forms, and a dark greenish-black streak; avoid prolonged moisture. A hardness or streak test is needed to distinguish pyrite from marcasite, limonite, or ordinary ironstone.