mineral

Aragonite

Aragonite (CaCO3)

Hardness: 3.5-4 (Mohs), Color: Colorless, white, yellow, or pale brown, Luster: Vitreous to resinous, Crystal Structure: Orthorhombic, Cleavage: Distinct in one direction, Specific Gravity: 2.95

Hardness: 3

Identified June 28, 2026More mineral →

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Physical properties

Hardness: 3.5-4 (Mohs), Color: Colorless, white, yellow, or pale brown, Luster: Vitreous to resinous, Crystal Structure: Orthorhombic, Cleavage: Distinct in one direction, Specific Gravity: 2.95

Formation & geological history

Forms in low-temperature environments near the Earth's surface, such as in hot springs, caves as stalactites, and as the shells of marine organisms like mollusks and corals.

Uses & applications

Used primarily as a collector's specimen and in some jewelry; it is also an important component in reef aquariums to maintain calcium levels.

Geological facts

Aragonite is chemically identical to calcite but has a different crystal structure, making them polymorphs. Most modern corals and pearl-bearing mollusks secrete aragonite for their skeletal structures.

Field identification & locations

Identified by its reaction to dilute hydrochloric acid (effervescence) and its pseudo-hexagonal crystal habits. Found commonly in sedimentary environments and limestone caves globally.