Pyrite with Calcite

Physical Properties

Pyrite: 6-6.5 Mohs hardness, metallic luster, brass-yellow color, cubic or pyritohedron crystal system. Calcite: 3 Mohs hardness, vitreous luster, colorless to yellow/white, rhombohedral crystals.

Formation & Geological History

Formed in hydrothermal veins and sedimentary deposits where iron and sulfur-rich fluids crystallize. This combination often occurs in low to medium temperature environments over millions of years.

Uses & Applications

Major ore for sulfur and sulfuric acid production; popular collector specimen; used in jewelry (as 'marcasite'); historical use in igniting gunpowder.

Geological Facts

Also known as 'Fool's Gold' because its metallic luster and brassy hue often led prospectors to mistake it for real gold. Pyrite can create sparks when struck against steel.

Field Identification & Locations

Identify by its distinct cubic metal-like crystals and 'striations' (fine lines) on crystal faces. Calcite can be identified by its reaction (fizzing) with weak acids. Commonly found in Spain, Peru, and various US states.

Identified on: 4/20/2026

Mode: Standard