Pilsenite

Chemical formula: Bi<sub>₄</sub>Te<sub>₃</sub>

Pilsenite is a rare bismuth telluride, characterized by a metallic luster, silvery-white color, and perfect cleavage.

## Characteristics Pilsenite is a bismuth telluride, belonging to the telluride group. Typical specimens occur as platy, scaly, or granular aggregates embedded in the host rock, most commonly quartz. It rarely forms small, hexagonal tabular crystals. Its color is silvery-white to tin-white, often with a dull, gray or yellowish oxide tarnish on weathered surfaces. ## Physical Properties This mineral is very soft, with a Mohs hardness of 1.5-2.5, meaning it can be scratched with a fingernail. It is opaque and has a strong, metallic luster. One of its most characteristic features is its very high density, approximately 8.41 g/cm³, which makes even small specimens surprisingly heavy. It has perfect cleavage in one direction, causing it to easily split into thin, inelastic lamellae. ## Colors and Varieties Pilsenite occurs in a uniform, silvery-white or tin-white color. Over time, it may develop a patina ranging from gray to yellowish. No distinct color varieties or commercial names are recognized. ## History and Name The mineral's name comes from its type locality – the city of Pilsen (German: Pilsen) in the Czech Republic. It was first described in 1853 by the Austrian mineralogist and geologist Felix Xaver Maximilian Zippe. ## Uses Due to its rarity, pilsenite has no industrial significance. It is solely an object of interest for collectors and scientists.

Properties

Mohs hardness: 1.5-2.5
Luster: Metallic
Streak: Dark gray to black
Density: 8.41
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Opaque
Crystal system: Trigonal

Diagnostic features

## Identification Key diagnostic features include its silvery-white color, strong metallic luster, very low hardness (scratches with a fingernail), and perfect cleavage in one direction, causing it to break into thin lamellae. Its very high density is also an important indicator. ## Distinguishing from Similar Minerals Pilsenite is macroscopically almost impossible to distinguish from other bismuth tellurides, such as tellurobismuthite (Bi₂Te₃) and tetradymite (Bi₂Te₂S), with which it often coexists. Definitive identification requires advanced analytical methods (e.g., XRD, EDS). It differs from native bismuth by its distinct cleavage (bismuth is more malleable). Molybdenite, although similarly soft and cleavable, has a characteristic bluish tint and is much lighter. ## Crystal Forms It most commonly occurs as platy, scaly, or granular aggregates. Small, tabular crystals with a hexagonal outline are rare.

Geological environment

## Genesis Pilsenite is a mineral of hydrothermal origin. It forms in medium to high-temperature ore veins, usually in association with gold and other bismuth minerals. ## Mineral Associations It most commonly coexists with native bismuth, gold, tellurobismuthite, tetradymite, hessite, altaite, chalcopyrite, pyrite, and quartz. ## Localities Classic and most important localities include Săcărâmb (formerly Nagyág) in Romania and the gold deposits in the Kalgoorlie region of Western Australia. It also occurs in Boliden, Sweden, in mines in Colorado (USA), and in the Robb Lake area in Ontario (Canada). Specimens from the type locality in the Czech Republic are historical and very rare.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued specimens are those with rich, well-visible pilsenite aggregates in a quartz matrix. Rare, well-formed crystals are exceptionally sought after. Coexistence with other rare minerals, especially visible native gold, adds significant value. ## Popular Localities The most prized specimens by collectors come from the historic locality of Săcărâmb in Romania and from mines in the Kalgoorlie region of Australia.

Care and storage

## Cleaning Pilsenite is extremely delicate. To remove dust, use only a soft brush or a stream of compressed air. Avoid contact with water and any chemical agents. ## What to Avoid The mineral is very soft and susceptible to scratches. Its perfect cleavage makes it brittle and easily delaminated under pressure or impact. It should be protected from moisture and sudden temperature changes, which can accelerate oxidation processes. ## Storage Pilsenite specimens are best stored separately in padded display boxes to avoid contact with harder minerals.

Sources

IMA Mineral List (CNMNC)