Aragonite / Calcite Geode

Physical Properties

Hardness: 3-4 (Mohs scale), Color: Colorless to white/pale yellow with orange-brown iron staining, Luster: Vitreous to pearly, Crystal structure: Orthorhombic or Trigonal, Cleavage: Perfect rhombohedral

Formation & Geological History

Formed through the precipitation of calcium-rich groundwater in sedimentary cavities or volcanic rock voids. This piece appears to be a smaller vug or geode portion often found in desert environments.

Uses & Applications

Primarily used for geological collecting, decorative display, and metaphysical purposes. Industrial uses of calcium carbonate include cement production and agricultural lime.

Geological Facts

Aragonite and Calcite are polymorphs; they share the same chemical formula but have different crystal structures. Over long geological time scales, aragonite often converts into calcite.

Field Identification & Locations

Identify in the field by its crystal habit and a positive reaction (fizzing) when exposed to a drop of weak acid (dilute HCl or vinegar). Often found in limestone caves or weathered sedimentary outcrops.

Identified on: 4/20/2026

Mode: Standard