Fettelite

specimen number:
2273022

location:
Glasberg quarry, Nieder-Beerbach, Hesse, Germany

description:
Sparse deep red crude micro crystals of the rare mineral fettelite on matrix.

The Glasberg quarry, situated near Nieder-Beerbach within the Muehltal municipality of Hesse, Germany, is a well-known industrial aggregate operation noted for its unique vein mineralization. Geologically, the quarry is excavated into the gabbro-diorite intrusive plutonism of the crystalline Odenwald complex, where a series of late-stage, low-temperature hydrothermal veins cut through the mafic igneous host rock. These specialized fissures are richly mineralized with native silver and complex silver, arsenic, and mercury sulfosalts. Commercial quarrying for road stone and industrial aggregate at the site began in the mid-nineteenth century, around 1866, and continued actively for over a century, providing an exceptional window into deep-seated European hydrothermal vein systems.

Fettelite is an exceedingly rare silver mercury arsenic sulfosalt mineral that crystallizes in the monoclinic system. Geologically, it occurs as a late-stage primary mineral within low-temperature hydrothermal veins that slice through crystalline mafic rocks like gabbro and diorite. The mineral typically forms microscopic, hexagonal-shaped flakes, tabular crystal plates, or rosette-like aggregates that exhibit a dark violet-red to deep scarlet-red coloration and a distinct submetallic to adamantine luster. First discovered and described from samples collected at the Glasberg quarry, which serves as its type locality.

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