Aragonite, is a naturally occurring stable form of calcium carbonate and a polymorph of calcite.  Aragonite is a low temperature and near surface mineral, that over time converts to calcite with accompanying changes in the environment.  

Aragonite is the main component of many organic substances, such as pearl and coral. The iridescent surface of Pearl and mother-of-pearl is actually a layer of Aragonite secreted by mollusks and related invertebrates.

Aragonite was named by Abrahan Gottlieb Werner after Molina de Aragón, Spain, the type locality where this mineral was first described.