Epistilbite

specimen number:
1052803

location:
Berufjorour, Djupavogshreppur, Mulaping, Eastern Region, Iceland

description:
Colorless crystals of epistilbite on matrix. Good locality example for the species. The specimen comes with an antique label as shown at the end of the video. This label gives an acquisition date of 1903.

The Berufjordur fjord region, located in eastern Iceland, is a classic geological and historical locality highly celebrated for its spectacular occurrences of secondary zeolite minerals. Geologically, the area is part of a deeply eroded, thick pile of late Miocene basaltic lava flows that were subsequently intruded by central volcanic complexes and extensive dyke swarms. Over time, low-temperature hydrothermal fluids circulated through the permeable vesicular cavities and fractures within these thick basalt layers, allowing rich suites of zeolites to crystallize. While there was never large-scale industrial mining or commercial quarrying on a traditional scale, small-scale surface extraction and organized mineral specimen collecting began in the nineteenth century, most notably at the famous nearby farm site of Teigarhorn, which was declared a protected natural monument in the twentieth century.

Epistilbite is a relatively rare silicate mineral belonging to the zeolite group, typically forming in low-temperature hydrothermal environments within the amygdaloidal cavities of basaltic and volcanic host rocks. Geologically, it crystallizes alongside other zeolites like stilbite, heulandite, and scolecite, though it develops under slightly different chemical parameters and temperature conditions. It commonly occurs as colorless, white, or light pink prismatic to tabular crystals that frequently form distinctive twin habits or radiating, fan-like aggregates with a vitreous to pearly luster. Because it closely resembles stilbite and other related species in hand samples, distinguishing epistilbite accurately from its counterparts often requires precise measurement of interfacial angles or detailed analytical testing.

The Heidelberger Mineralien-Comptoir (often referenced or later spelled as Mineralien-Contor or Comptoir in historical trade registers) was a pioneering commercial mineralogical establishment based in Heidelberg, Germany. Originally established in the early nineteenth century by the famed mineralogist Carl Caesar von Leonhard, the dealership evolved through various successions, including management by J. Lommel into the late nineteenth century, and it maintained an active presence into the early twentieth century by providing reference collections to institutions globally. Operating during an era when German commercial houses dominated the global natural history trade, this enterprise systematically acquired, cataloged, and sold mineral specimens, rocks, and wooden crystallographic models to universities, public museums, and serious private collectors worldwide.

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