Fluorite on Quartz Epimorph after Calcite

From Second Chance Mine in Tombstone, Arizona, this dramatic pseudomorph showcases the intriguing mineralogy of this locality. Octahedral fluorites with a soft purple glow fill an epimorph of quartz after calcite. The scalenohedral morphology of the calcites is well preserved by an attractive crystalline cast of snowy white quartz. An opening on one side shows the beautiful mineralization of purple fluorite within. An epimorph is a specific type of pseudomorph. In an epimorph, one mineral forms as a coating along the surfaces of another, and the original mineral later dissolves, leaving a cast of its shape behind. This replacement and dissolution occurred at this locality in heavily fractured limestones, where hydrothermal fluids moved through the rock, depositing quartz on calcite while dissolving the calcite itself. The process points to an acidic environment, since quartz forms under the same conditions that dissolve calcite. Once the quartz pseudomorphs had formed, fluorite filled the voids around them.