Pyrite after Pyrrhotite with Siderite, Sphalerite

specimen number:
2312016

location:
Turt Mine, Satu Mare Co., Romania

description:
Thick pseudo-hexagonal crystals of what were once pyrrhotite measuring to 4.0 cm in size, these now replaced by crystalline pyrite and scattered across the top of a crystallized quartz matrix with much siderite and minor sphalerite. In great condition. Very choice for this now long closed locality.

The Turt Mine, located in the Oas Mountains of Satu Mare County in northwestern Romania, is situated within a prolific metallogenic region associated with Neogene volcanism along the Inner Carpathians. The local geology is characterized by volcanic and subvolcanic structures where hydrothermal activity deposited complex polymetallic ore veins containing lead, zinc, and copper sulfides. Mining operations in the area date back generations to extract these base metals. The underground workings became well known among mineral collectors for producing fine specimens of galena, often associated with siderite, pyrite, and other sulfide minerals, before industrial extraction eventually ceased.

Pseudomorphs occur when one mineral chemically replaces another while preserving the original crystal shape and external morphology. A classic example of this process is pyrite after pyrrhotite. Pyrrhotite, an iron sulfide with a hexagonal crystal system, typically forms under high-temperature conditions. As geochemical environments shift and fluids circulate through a deposit, the original pyrrhotite crystals become unstable and undergo dissolution-reprecipitation. Through this replacement mechanism, iron disulfide precipitates as pyrite, faithfully replicating the distinct tabular or hexagonal forms of the precursor pyrrhotite even though the internal mineral composition changes.

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