Dolomite after Calcite with Quartz

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A large rhombohedral crystal of what was once calcite 8.0 cm across coming off of a quartz crystal matrix and replaced by crystallized dolomite. In terrific condition all around.The Krushev Dol mine, situated within the renowned Madan ore field in the Rhodope Mountains of southern Bulgaria, has a rich mining history dating back to ancient Thracian times in the fourth century BC, with extensive modern industrial development taking place through the twentieth century. Geologically, the deposit is part of a complex hydrothermal vein and replacement system hosted within high-grade metamorphic rocks and marbles, shaped by intensive Paleogene magmatic and tectonic activity. Mineralogically, the mine is world-famous for producing exceptional collector specimens, particularly lustrous galena, sphalerite (including notable cleophane varieties), chalcopyrite, and quartz, alongside a diverse array of associated sulfides and rare accessory minerals.Pseudomorphs of dolomite after calcite occur when calcium magnesium carbonate replaces calcium carbonate while preserving the original crystal morphology. Geologically, this transformation typically takes place in sedimentary or hydrothermal environments where circulating fluids rich in magnesium alter precursor calcite crystals. Historically, these specimens have fascinated mineralogists because they record changing fluid chemistry over time, allowing researchers to reconstruct the complex geochemical evolution of mineral deposits.