Dolomite after Calcite

specimen number:
2312472

location:
Cavnic, Maramures Co., Romania

description:
A cluster of what were once rhombohedral crystals of calcite, this now completely replaced by crystallized dolomite. Crystallized completely all around with no points of attachment and in great condition.

Cavnic, located in the Maramures region of northern Romania, is a historic mining district with metal extraction dating back to medieval times and sustained commercial operations through the twentieth century. Geologically, the area is situated within the Neogene volcanic belt of the Eastern Carpathians, where epithermal vein deposits formed through hydrothermal activity associated with calc-alkaline volcanism. Mineralogically, the district is world-famous for its rich polymetallic sulfide veins, producing exceptional, highly aesthetic museum specimens of quartz, rhodochrosite, calcite, sphalerite, galena, and various sulfosalts that are treasured by collectors globally.

Pseudomorphs of dolomite after calcite occur when a precursor crystal of calcite is chemically altered or replaced by dolomite while preserving the original crystal's external geometric form. This geological phenomenon typically happens when hydrothermal solutions or groundwater rich in magnesium ions interact with preexisting calcium carbonate crystals under specific temperature and chemical conditions. Mineralogically, the process involves the introduction of magnesium to replace a portion of the calcium ions in the crystal lattice, transforming the mineral structure from calcite to dolomite without altering the distinctive scalenohedral, rhombohedral, or prismatic shapes dictated by the original calcite template.

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