mineral
Aragonite Star Cluster (Cross-section)
Aragonite (Calcium Carbonate, CaCO3)
Hardness: 3.5-4 Mohs. Color: Reddish-brown, cream, white. Luster: Vitreous to resinous. Structure: Orthorhombic, often forming pseudo-hexagonal twinned crystals. Cleavage: Distinct in one direction.
- Hardness
- 3
- Color
- Reddish-brown, cream, white
- Luster
- Vitreous to resinous
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Physical properties
Hardness: 3.5-4 Mohs. Color: Reddish-brown, cream, white. Luster: Vitreous to resinous. Structure: Orthorhombic, often forming pseudo-hexagonal twinned crystals. Cleavage: Distinct in one direction.
Formation & geological history
Formed in low-temperature hydrothermal environments or near-surface sedimentary environments through chemical precipitation. These specific twinned crystals are common in oxidized zones of ore deposits and sedimentary basins.
Uses & applications
Primarily used as educational mineral specimens and for metaphysical or decorative purposes. Historically used as a source of lime, though calcite is more common for that purpose.
Geological facts
Aragonite is a polymorph of Calcite, meaning they share the chemistry but have different crystal structures. It is also the primary component of many sea shells and pearls. The 'star' shape is due to cyclic twinning of multiple crystals together.
Field identification & locations
Can be identified by its pseudo-hexagonal shape and the radiating 'star' pattern visible in cross-sections. In the field, look for them in gypsiferous marls or hot spring deposits. They will effervesce (fizz) in contact with dilute hydrochloric acid.
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