Fluorescent calcite (probable)

Small pale-white translucent crystal aggregate viewed under ultraviolet light, producing a violet-blue appearance from the lighting; calcite has Mohs hardness 3, vitreous-to-pearly luster, trigonal crystal structure, and perfect rhombohedral cleavage. The image is low-resolution, so fluorescence and exact crystal form are uncertain.

Calcite commonly forms by precipitation from groundwater, hydrothermal fluids, or marine sediments, ranging from recent deposits to Precambrian occurrences. Fluorescence is caused by trace activator elements such as manganese or lead.

Used extensively in cement, lime, construction aggregate, chemical processing, and optical calcite; attractive fluorescent specimens are collected. Typical small specimens are worth about $5–$30, with exceptional crystals or strong fluorescence reaching $50–$200+.

Calcite is readily identified by vigorous effervescence in dilute hydrochloric acid and by its low hardness. Common localities include Mexico, the United States, Iceland, China, and Morocco.

Look for rhombohedral cleavage and acid reaction; do not rely on the purple color because it likely comes from ultraviolet illumination. A scratch test with a copper coin can help confirm its softness, but may damage the specimen.