Quartz after Calcite with Pyrite, Sphalerite

specimen number:
2312448

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

description:

A cluster of what were once scalenohedral crystals of calcite, these now completely replaced and hollowed out by sparkling crystallized quartz. Small crystals of pyrite and sphalerite are scattered throughout. In great condition. Sphalerite crystal shows some translucency.

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.

Quartz after calcite pseudomorphs are fascinating mineral specimens where secondary quartz has completely replaced earlier crystals of flat, tabular, or blade-like calcite. Geologically, these formations typically develop in hydrothermal or low-temperature sedimentary environments when changing chemical conditions cause acidic solutions to dissolve the original calcium carbonate calcite while simultaneously depositing silica.

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