Aragonite (CaCO₃) is the orthorhombic polymorph of calcium carbonate, distinct from calcite by its denser packing and pseudo-hexagonal twinning. It forms acicular sprays, “flos ferri” branching coral-like masses, and pseudo-hexagonal twins. Famous worldwide from Molina de Aragón (Spain — the type locality) and Erzberg (Austria).
Key Facts
- Mohs hardness 3.5–4 — slightly harder than calcite.
- Orthorhombic; converts to calcite over geological time at surface conditions.
- Forms cyclic pseudo-hexagonal twins (visible from prism faces).
- Common in mollusk shells, coral skeletons, and stalactite caves.
- “Flos ferri” variety: white, branching, coral-like masses from Erzberg, Austria.
Notable Localities
Molina de Aragón (Spain) is the type locality. Erzberg (Austria) produces flos ferri. China has minor occurrences in Hubei.
Found at these Localities
- Filipinas Mine (Los Chupaderos) (菲利皮纳斯矿(拉利玛产地))
- Hubei (湖北)
