Aragonite - CaCO₃

Habit: Colorless or white; also gray, pale shades of yellow, blue, violet, green or red. Short to long prismatic isolated crystals or acicular, dipyramidal or thick tabular; also as columnar crystal aggregates and crusts, globular, reniform, pisolitic, coralloidal, stalactitic, internally fibrous or banded. Vitreous luster, resinous on fracture surfaces; transparent to translucent. White streak.

Environment: Typically forms in low-temperature environments and near the surface; relatively unstable and can alter to calcite. Also occurs as speleothemes in limestone caves, as pisolites, sinters and massive lamellar deposits at geysers and hot springs, and as a replacement mineral in various rock types and ore deposits.

Etymology: Named for where it was first described from, Molina de Aragón, Spain. When aragonite occurs as coral-like aggregates in iron ore deposits in association with siderite (its iron carbonate counterpart), it is called flos ferri, meaning "flowers of iron."