Bergslagite

Chemical formula: CaBe(As<sup>5+</sup>O<sub>4</sub>)(OH)

Bergslagite is a rare calcium beryllium arsenate, forming colorless to white, tabular crystals, prized by collectors of rare minerals.

## Characteristics Bergslagite is a rare mineral from the arsenate group, chemically classified as a hydrated calcium beryllium arsenate. It occurs as small, tabular or bladed crystals, rarely exceeding 1 mm in length. Crystals are typically colorless, white, or pale gray and form radial, rosette-like aggregates or appear as single, overgrown crystals in vugs and rock fissures. ## Physical Properties This mineral is characterized by a hardness of approximately 5 on the Mohs scale. It has a vitreous luster and is transparent to translucent. Its density is about 3.43 g/cm³. It does not exhibit fluorescence under ultraviolet light. ## Colors and Varieties Bergslagite is usually colorless to white, sometimes with a gray tint. No named color varieties or commercial varieties have been distinguished. ## History and Name The mineral's name comes from the Bergslagen region in central Sweden, where it was discovered. It was described and approved as a new mineral by the International Mineralogical Association (IMA) in 1993. The discovery was made by P.J. Dunn, D.R. Peacor, F.J. Wicks, and R.A. Ramik. ## Uses Bergslagite has no industrial application. Its significance is purely scientific and collectible, being a sought-after mineral due to its rarity and origin from a classic mineralogical locality.

Properties

Mohs hardness
5
Luster
Vitreous
Streak
White
Density
3.43
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Bergslagite is difficult to identify visually without specialized equipment. It is recognized by its characteristic tabular or bladed crystal habit, often forming radial aggregates. It occurs in a specific geological environment – in skarns. Definitive identification requires advanced analytical methods such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals It can be confused with other rare arsenates or silicates of similar appearance, such as datolite or herderite, which also form colorless or white crystals. Differentiation is based on chemical composition analysis (presence of arsenic and beryllium) and crystallographic data. ## Crystal Forms Crystals are monoclinic, with a tabular or bladed habit, elongated along the crystallographic axis. They often form fan-shaped or radial aggregates, as well as small, overgrown crystals in rock cavities.

Geological environment

## Genesis Bergslagite forms as a result of metamorphic processes within manganese and iron skarns. It crystallizes in fissures and vugs, forming in the late stage of deposit formation, often in association with other arsenic and beryllium minerals. ## Mineral Associations This mineral co-occurs with other rare minerals such as svabite, berzeliite, manganberzeliite, tephroite, magnetite, hematite, barite, fluorapatite, and hausmannite. Its occurrence in association with these minerals is an important diagnostic clue. ## Localities The most important and type locality (localitas typica) for bergslagite is the Långban mine in Filipstad Municipality, Bergslagen region, Sweden. This is a historical and world-renowned locality, famous for the occurrence of many rare and unique minerals. Besides Långban, its presence has also been reported in the Jakobsberg and Sjögruvan mines, also in Sweden.

Rarity

Very rare

For collectors

## Quality Criteria The most prized bergslagite specimens are those with well-formed, sharp, and undamaged crystals, forming aesthetic, radial aggregates. Contrast with the rock matrix and the presence of associated minerals that confirm its origin are also important. Due to the small size of the crystals, specimens visible to the naked eye are particularly sought after. ## Popular Localities The only source of valuable collector specimens is the historic Långban mine in Sweden. Specimens from this locality are the standard for this mineral and command the highest prices in the collector's market.

Care and storage

## Cleaning Specimens should be cleaned mechanically only, using a soft brush to remove dust. Due to its rarity and potential fragility, avoid washing in water, especially in ultrasonic cleaners. ## What to Avoid Avoid contact with acids and other chemicals that may damage the crystal surface. The mineral is stable, but it should be protected from strong impacts and scratching by harder minerals. ## Storage It is recommended to store specimens in separate, enclosed collector boxes (e.g., "membrane box" or foam-lined box) to protect delicate crystals from mechanical damage and dust. Avoid exposure to moisture and extreme temperatures.

Sources

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