sedimentary (matrix) / mineral (inclusion)

Pyrite on Limestone

Iron Disulfide (FeS2) in Calcium Carbonate (CaCO3) matrix

Hardness: 6-6.5 (Pyrite), 3 (Limestone). Color: Brass-yellow (Pyrite), beige/tan (Limestone). Luster: Metallic for the mineral; dull/earthy for the rock. Crystal structure: Isometric (cubes, pyritohedrons).

Hardness: 6-6
Color: Brass-yellow (Pyrite), beige/tan (Limestone)
Luster: Metallic for the mineral

Identified March 21, 2026More sedimentary (matrix) / mineral (inclusion) →

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Physical properties

Formation & geological history

Formed in low-oxygen marine sedimentary environments where organic matter decays, releasing sulfur that reacts with iron in the water. These deposits can range from the Paleozoic era to the present.

Uses & applications

Pyrite is used as a source of sulfur and in sulfuric acid production, though mainly collected as 'Fool's Gold.' Limestone is vital for construction, concrete, and agricultural lime.

Geological facts

Pyrite gets its name from the Greek word 'pyr' (fire) because it creates sparks when struck against metal. It is often mistaken for gold, though gold is much softer and lacks the crystalline structure.

Field identification & locations

Identify in the field by the metallic golden glint against a dull, soft host rock. Can be found globally in sedimentary basins. Collectors should look for distinct cubic shapes or 'sun' radiated formations.

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