mineral

Aragonite (Star Cluster or Twinned variety)

Aragonite (Calcium Carbonate, CaCO3)

Hardness: 3.5-4 (Mohs); Color: Reddish-brown, tan, or white; Luster: Vitreous to resinous; Crystal structure: Orthorhombic (often forming pseudo-hexagonal twinned prisms); Cleavage: Distinct in one direction.

Hardness: 3
Color: Reddish-brown, tan, or white
Luster: Vitreous to resinous

Identified March 20, 2026More mineral →

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Physical properties

Formation & geological history

Forms in low-temperature near-surface environments, often through precipitation from hot springs (travertine) or in oxidizing zones of ore deposits. The cyclic twinning seen here creates 'star' or 'cogwheel' shapes. Most of these specimens originate from Morocco or Spain.

Uses & applications

Primarily used as a mineral specimen for collectors and in metaphysical practices. Occasionally used for small ornamental carvings or as a source of calcium in biological filters/aquariums.

Geological facts

Aragonite is a polymorph of Calcite, meaning they share the same chemical formula but have different crystal structures. It is also the main component of organic structures like mother-of-pearl (nacre) and pearls.

Field identification & locations

Identify in the field by its distinct hexagonal-shaped twinned prisms, reddish-brown hue, and a positive reaction (fizzing) when exposed to cold dilute hydrochloric acid. Commonly found in Morocco, Tazouta area.

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