Dolomite after Calcite

specimen number:
2312428

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

description:

A scalenohedral crystal of what was once calcite, this now replaced by crystallized dolomite, with a second-generation of scalenohedral calcite crystals. In great condition all around, note the hollow interior as shown in the video.

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.

Pseudomorphs of dolomite after calcite represent a fascinating mineralogical replacement process where an original crystal of calcite is chemically altered or replaced by dolomite while retaining its external crystal shape. Geologically, these forms typically develop when circulating hydrothermal or groundwater solutions rich in magnesium and iron interact with pre-existing calcium carbonate calcite crystals, altering the chemical environment until the original mineral is dissolved and substituted molecule by molecule. Mineralogically, the resulting specimens feature the distinct crystal habits of calcite, such as scalenohedra or rhombohedra, but possess the chemical composition and slightly different physical properties of dolomite, making them highly prized collector items for their preservation of the original form through geological time.

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