3.3" Iridescent Chalcopyrite and Calcite on Dolomite - Missouri

About Calcite Crystals

Calcite crystals are a form of calcium carbonate (CaCO₃) known for their diverse shapes, transparency, and vibrant range of colors. They typically form in rhombohedral, scalenohedral, or prismatic shapes, often with well-defined, sharp edges and glossy surfaces. Calcite crystals are often translucent or transparent, sometimes displaying a double refraction effect where objects viewed through the crystal appear doubled. They can appear in various colors—white, clear, yellow, pink, blue, green, and orange—depending on impurities or trace minerals.

A notable characteristic of calcite is its reaction with weak acids like vinegar, which causes it to effervesce, or fizz, as it releases carbon dioxide. This property makes calcite crystals a key tool in geological identification and studies. Calcite forms in many environments, from sedimentary rocks like limestone and marble to hydrothermal veins.

Chalcopyrite is a brass-yellow colored mineral and an important copper ore. When weathered, chalcopyrite loses its metallic luster, turning a gray-green color. When exposed to acids, the tarnish can develop a red, blue, or purple iridescence: this acid-treated material is often sold under the name peacock ore.