Formula: CaCO3

Colour: Colorless to white or grey, often stained various hues by impurities, such as blue, green, red or violet; colourless in transmitted light.

Lustre: Vitreous, Resinous

Hardness: 3½ – 4

Specific Gravity: 2.947

Crystal System: Orthorhombic

Member of: Aragonite Group

Name: Named in 1797 by Abrahan Gottlob Werner for the type locality, the village of Molina de Aragón, Spain, and not the province of Aragón, a mistake made by several later writers.

Type Locality: Gallo river, Molina de Aragón, Guadalajara, Castile-La Mancha – Spain

Polymorph of: Calcite

The principal member of the Aragonite Group, aragonite is the second most common polymorph of natural calcium carbonate (the most common is calcite). It is significantly less widespread and abundant than calcite and is formed under a much narrower range of physiochemical conditions. It is metastable relative to calcite and often converts to calcite accompanying changes in the environment.