mineral

Aragonite Star Cluster

Aragonite (Calcium Carbonate, CaCO3)

Hardness: 3.5-4 (Mohs); Color: Red-brown to orange-brown; Luster: Vitreous to resinous; Crystal structure: Orthorhombic (forming pseudo-hexagonal twinned crystals); Cleavage: Distinct in one direction; Specific gravity: 2.95.

Hardness: 3
Color: Red-brown to orange-brown
Luster: Vitreous to resinous

Identified February 14, 2026More mineral →

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Physical properties

Formation & geological history

Aragonite clusters typically form in low-temperature hydrothermal environments or near the Earth's surface in caves and sedimentary deposits. These specific twinned star clusters are famously formed through the precipitation of calcium carbonate in sedimentary environments, often found in Morocco.

Uses & applications

Primarily used as a mineral specimen for educational purposes and crystal collecting. It is sometimes used in jewelry as beads, though its low hardness makes it fragile. In industry, aragonite is used in soil pH buffering and as a source of calcium.

Geological facts

Aragonite is a polymorph of calcite, meaning they share the same chemistry but have different crystal structures. It is also the primary constituent of pearls and the mother-of-pearl (nacre) found in mollusk shells.

Field identification & locations

Identify in the field by its distinct 'starburst' or 'sputnik' habit, composed of hexagonal-looking twinned prisms. It reacts strongly (bubbles) to cold dilute hydrochloric acid. Commonly found in Morocco, Spain, and Mexico.

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