Aragonite

Physical Properties

Hardness: 3.5-4 (Mohs); Color: White, yellow, gold, brown; Luster: Vitreous to resinous; Crystal structure: Orthorhombic; Cleavage: Distinct in one direction; Specific gravity: 2.95.

Formation & Geological History

Forms by biological and physical processes in marine and freshwater environments as shells or pearls. Also forms as precipitates in hot springs, karst caves, and some metamorphic rocks through low-temperature hydrothermal activity.

Uses & Applications

Used primarily as decorative carvings, ornamental stones, jewelry beads, and as a calcium supplement in aquarium reef-building.

Geological Facts

Aragonite is a polymorph of Calcite, meaning it has the same chemical formula but a different crystal structure. It is the primary component of most mollusk shells and the pearly layer of nacre.

Field Identification & Locations

Identify in the field by checking for its characteristic 'sputnik' or needle-like crystal habit and its reaction (effervescence) to weak acid. Common in Spain, Morocco, Mexico, and the USA.

Identified on: 4/27/2026

Mode: Standard