Aragonito

Aragonite is an orthorhombic polymorph of calcium carbonate.

It forms by precipitation in sedimentary, hydrothermal and volcanic environments. It is frequent in low‑temperature settings, including lacustrine or marine deposits. It also occurs in cavities of carbonate rocks and as a secondary mineral in oxidation zones. It is less stable than calcite and can transform into it over time.

It may develop prisms and spear‑shaped twins. Fibrous, columnar, botryoidal or coral‑like aggregates, and radiating forms, are common. It develops stalactites that grow drop by drop and can show a bulbous or cotton‑like aspect.

The name “aragonite” refers to the type locality, Molina de Aragón (Guadalajara). At Pantoja, acicular crystals grow in cavities of lacustrine sedimentation and display fluorescence and phosphorescence; there they are known as “Pantojos” or “Aragonito Erizo”. At Toral de los Vados (El Bierzo), bluish specimens are locally called “Toralina”; their colour is linked to inclusions of rosasite or copper impurities. Blue Sardinian aragonite occurs as coralloid forms or massive columnar‑fibrous aggregates, with blue bands and whitish zones characteristic of the locality.

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