mineral

Pyrite with Limonite/Goethite Alteration (Pseudomorph)

Iron Sulfide (FeS2) transitioning to Hydrated Iron Oxides (FeO(OH)·nH2O)

Hardness: 6-6.5 (for pyrite core), 4-5.5 (for oxidation surface). Color: Brassy yellow inside, reddish-brown/orange/rust exterior. Luster: Metallic to earthy. Crystal structure: Cubic (isometric). Cleavage: Indistinct.

Hardness: 6-6
Color: Brassy yellow inside, reddish-brown/orange/rust exterior
Luster: Metallic to earthy

Identified March 14, 2026More mineral →

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Physical properties

Formation & geological history

Formed through hydrothermal processes or sedimentary precipitate in low-oxygen environments. The specimen shows chemical weathering where water and oxygen have begun converting the sulfide mineral into iron oxides over geological time.

Uses & applications

Major source of sulfur and iron in the past; currently used for sulphuric acid production, as an ornamental 'Fool's Gold' specimen, and occasionally in jewelry (marcasite style).

Geological facts

Known as 'Fool's Gold' because of its metallic luster. When it oxidizes, it can create 'limonite pseudomorphs after pyrite,' where the iron oxide takes the exact cubic shape of the original pyrite crystal.

Field identification & locations

Identify by its cubic/boxy shape and reddish-orange oxidation products. Common in mining districts and sedimentary shale beds. Collectors look for sharp edges and a lack of crumbling (pyrite rot).

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