Bergenite

Chemical formula: Ca₂Ba₄(U₆+O₂)₉O₆(PO₄)₆·₁₆H₂O

A rare uranium mineral from the phosphate group, forming characteristic, platy crystals of an intense yellow color.

## Characteristics Bergenite is a hydrated uranyl, barium, and calcium phosphate, belonging to the rare minerals. It forms very small, bladed or platy crystals, which usually arrange themselves into radial aggregates, rosettes, or fans. Specimens most often occur as thin crusts on the host rock. Its intense, golden-yellow or greenish-yellow color makes it easily noticeable despite the small size of the crystals. ## Physical Properties This mineral is characterized by a vitreous luster, transitioning to waxy on some surfaces. It is translucent. Its hardness on the Mohs scale has not been precisely determined. The calculated density is approximately 4.13 g/cm³. It exhibits perfect cleavage in one direction. ## Colors and Varieties Bergenite occurs in shades from bright yellow and golden-yellow to greenish-yellow. No color or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – a uranium deposit near the town of Bergen in Vogtland (Saxony, Germany). It was first described in 1959 by H.W. Bültemann and Paul Ramdohr. ## Uses Due to its rarity and small accumulations, bergenite has no industrial application. It is solely an object of scientific interest and a valued acquisition for advanced mineral collections, especially those specializing in uranium minerals.

Properties

Luster: Vitreous to Waxy
Streak: Yellow
Density: 4.13
Cleavage: Perfect on {010}
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification The key diagnostic feature of bergenite is its form – thin, platy crystals gathered in radial aggregates and rosettes of a bright yellow color. A very important feature is also strong radioactivity, detectable with a Geiger counter. It occurs as small crusts on rocks. ## Distinguishing from Similar Minerals Bergenite can be confused with other secondary yellow uranium minerals, such as autunite, uranophane, or phosphuranylite. It is distinguished from autunite by the absence or very weak fluorescence under UV light. Uranophane most often forms acicular or fibrous aggregates, not platy rosettes. Final distinction from the very similar phosphuranylite requires advanced chemical analysis (detection of barium). ## Crystal Forms Crystals are thin-platy, bladed, elongated. They almost always occur in characteristic, radial or stellate aggregates, as well as fan-shaped clusters and thin coatings.

Geological environment

## Genesis Bergenite is a secondary uranium mineral. It forms in the oxidation (weathering) zones of uranium deposits, in an environment rich in phosphorus and barium. It is formed as a result of the alteration of pre-existing uranium minerals, mainly uraninite. ## Mineral Associations It most often co-occurs with other secondary uranium minerals, such as phosphuranylite, torbernite, autunite, dewindtite, uranophane, and uranocircite. It is also accompanied by quartz and hematite. ## Localities This is a very rare mineral, known from only a few localities worldwide. The most important and type locality is the area of Bergen in Saxony (Germany), where it was discovered. Specimens from there come from old dumps of former uranium mines.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued specimens are those with rich, well-formed rosettes or fan-shaped crystal aggregates of an intense, golden-yellow color. The aesthetic arrangement of aggregates on the host rock (matrix) and the absence of damage to delicate crystals are also important. Contrast with a dark rock background enhances visual appeal. ## Popular Localities By far the most known and valued specimens come from the type locality – the vicinity of Bergen in Saxony, Germany. This is a classic locality for this mineral, and most of the specimens available on the collector's market originate from there.

Care and storage

## Warning **Radioactive mineral.** Handle with caution. Avoid inhaling dust and direct, prolonged skin contact. Wash hands thoroughly after each contact with the specimen. Do not store in areas of permanent human presence (desks, bedrooms). ## Cleaning Only mechanical cleaning is recommended, using a soft brush or compressed air to remove dust. Avoid contact with water and any chemical agents. ## What to Avoid Avoid ultrasonic cleaners, high temperatures, and exposure to chemicals and acids, which can permanently damage the delicate crystals. ## Storage Bergenite specimens should be stored in tightly sealed, labeled containers (e.g., "perky box" type) to limit radon emission. The collection should be kept in a well-ventilated room, away from photosensitive materials.