mineral

Likely weathered pyrite nodule

Pyrite (FeS₂), possibly a small marcasite/pyrite concretion

AI-generated identification · may be incorrect

Dark gray-bronze, metallic to dull luster with granular or radiating surface; pyrite hardness 6–6.5 Mohs, cubic crystal structure, no obvious cleavage, and specific gravity about 5.0. The specimen appears rounded and oxidized, so its original brassy color may be obscured.

Identified September 8, 2026More mineral →

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Physical properties

Formation & geological history

Forms in sulfur-rich, reducing environments such as sedimentary rocks, hydrothermal veins, and coal deposits; individual nodules may be Paleozoic to much younger. Surface oxidation converts pyrite to iron oxides and sulfates, producing darker, weathered coatings.

Uses & applications

Used industrially as a sulfur source and historically for sulfuric-acid production; attractive crystals are collected, but this small weathered piece has little jewelry value.

Geological facts

Pyrite is commonly called “fool’s gold,” though its hardness, brittleness, darker streak, and lack of malleability distinguish it from gold. Marcasite has the same chemistry but is less stable and often decomposes in humid air.

Field identification & locations

Look for a metallic sheen, heavy feel, dark greenish-black streak, and resistance to scratching by a steel knife; avoid prolonged moisture because oxidation can cause “pyrite disease.” Common worldwide, especially Spain, Peru, Italy, China, and sedimentary regions.