Calcite after Gypsum

specimen number:
2312537

location:
Boldut Mine, Cavnic, Maramures Co., Romania

description:
A loose cluster of what were once crystals of gypsum, these now replaced by white crystalline calcite. In excellent condition all around with no points of attachment. Classic pseudomorph specimen for this famous locality.

The Boldut Mine, located within the Cavnic mining district of Maramures County, Romania, is part of a historic mining region with roots dating back to medieval times and earlier, while intensive industrial extraction of its polymetallic ores operated heavily through the 20th century until final closure around 2005. Geologically, the deposit sits within the Neogene volcanic belt of the Inner Carpathians, where hydrothermal activity driven by calc-alkaline magmatism emplaced rich veins of lead, zinc, copper, gold, and silver into volcanic and sedimentary host rocks. The underground workings became internationally renowned among mineral collectors for producing diverse sulfide and carbonate assemblages, including quartz, dolomite, rhodochrosite, calcite, sphalerite, and galena.

Calcite after gypsum is a fascinating mineralogical pseudomorph where calcium carbonate replaces an original crystal of calcium sulfate while preserving the external crystal shape. Geologically, these formations typically develop in sedimentary settings or evaporite deposits where changing geochemical conditions, such as fluctuations in fluid chemistry or rising carbonate concentrations, cause the original gypsum to dissolve while simultaneously precipitating calcite to fill or coat the resulting mold. Mineralogically, these specimens successfully capture the distinctive monoclinic blade or swallowtail twin habits of gypsum.

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