Siderite after Calcite

specimen number:
2312336

location:
Turt Mine, Satu Mare Co., Romania

description:
Crystallized groupings of what were once calcite to 4.7 cm in diameter across a galena matrix with pyrite. These are now completely replaced by reddish-brown crystallized siderite. In great condition.

The Turt Mine, located in Satu Mare County within the northern mining region of Romania, is part of the broader Baia Mare metallogenic province. Geologically, the deposit is hosted within complex Neogene volcanic and sedimentary structures, featuring massive polymetallic ore veins that historically reached up to twenty meters in thickness. The mineralogy of the deposit is heavily defined by base metal sulfides such as galena, pyrite and sphalerite, alongside notable occurrences of siderite, often replacing calcite. Mining operations date back centuries, contributing significantly to the region's industrial output of lead, zinc, and associated metals before commercial production ultimately ceased.

Pseudomorphs of siderite after calcite form through geological replacement processes in hydrothermal or sedimentary environments where iron-rich carbonate solutions circulate through rock formations containing calcium carbonate crystals. Over time, the original calcite dissolves and is systematically replaced by siderite, resulting in a mineral specimen that retains the external crystal morphology of the parent calcite while its internal chemistry shifts to iron carbonate. Historically, these remarkable specimens have fascinated mineralogists and collectors since they provide clear evidence of changing hydrothermal fluid chemistry and secondary alteration processes within ore deposits.

Questions about this specimen?
Send an email or call us: 314-341-1811.