Bartelkeite

Chemical formula: Pb<sup>2+</sup>Fe<sup>2+</sup>Ge(Ge<sub>2</sub>O<sub>7</sub>)(OH)<sub>2</sub>·H<sub>2</sub>O

Bartelkeite is a very rare, hydrated lead-iron germanate, forming small, tabular, white crystals.

## Characteristics Bartelkeite is an extremely rare mineral from the germanate group. It occurs as very small, bladed or tabular crystals, which usually do not exceed 0.5 mm in length. These crystals are colorless to white and form small, radial aggregates or occur as single, scattered flakes on the surface of other minerals, mainly germanite. ## Physical properties Bartelkeite crystals exhibit a vitreous luster. Due to the small size of the crystals, most physical properties, such as hardness or density, have not been precisely determined. The density calculated based on the chemical formula and unit cell parameters is 5.35 g/cm³. ## Colors and varieties This mineral is usually colorless to white. No varieties have been distinguished. ## History and name Bartelkeite was discovered in the Tsumeb mine in Namibia, which is its only known locality. It was described in 1981 by Peter G. Keller, Heinz Hess, and Paul B. Moore. The mineral is named in honor of Wolfgang Bartelke, a German mineral collector from Tsumeb, who first noticed this mineral and made it available for research. ## Applications Due to its extreme rarity and microscopic size, bartelkeite has no practical applications. It is solely an object of scientific and collecting interest for specialized collectors of Tsumeb minerals or rare minerals.

Properties

Luster
Vitreous
Streak
White
Density
5.35
Cleavage
Perfect on {100}
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of bartelkeite is based on its appearance – small, white, tabular crystals sometimes forming radial aggregates. A key indicator is its occurrence on germanite in material from the Tsumeb mine. Definitive identification is only possible using advanced analytical methods, such as X-ray diffraction (XRD) or electron spectroscopy (EDS). ## Distinguishing from similar minerals At first glance, it may be confused with other secondary, white minerals found in Tsumeb, such as anglesite or cerussite. However, bartelkeite is distinguished by its characteristic form of thin, tabular crystals and its specific co-occurrence with germanite. Other germanates, such as stottite, usually have a different crystal form. ## Crystal forms It forms thin, tabular or bladed crystals, often elongated and flattened. These crystals can occur individually or form small, radial aggregates.

Geological environment

## Genesis Bartelkeite is a secondary mineral that formed in the oxidation zone of the polymetallic deposit in Tsumeb. It crystallizes at low temperatures from solutions rich in germanium, formed as a result of the weathering of primary sulfides containing this element, mainly germanite. ## Mineral associations This mineral occurs in close association with germanite, on which it most often grows. It also co-occurs with galena, tennantite, stottite, and brunogeierite. ## Localities The only confirmed locality of bartelkeite in the world is the Tsumeb mine in the Oshikoto Region, Namibia. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality criteria The quality of a bartelkeite specimen is assessed primarily based on the abundance and visibility of its crystals. The most desirable specimens are those with numerous, well-formed, white crystals, forming distinct aggregates on a contrasting matrix, which is most often metallic germanite. The size of individual crystals, although always microscopic, also affects the value – the larger and better-formed they are, the more valuable the specimen. ## Popular localities The only source of bartelkeite specimens is the historic Tsumeb mine in Namibia. All specimens available on the collector's market come from this single location.

Care and storage

## Cleaning Due to the extreme fragility and small size of the crystals, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used from a safe distance to remove dust. Avoid contact with water and any chemicals. ## What to avoid Avoid ultrasound, chemical agents (acids, solvents), high temperatures, and humidity. Any physical contact, including touching, can permanently damage the delicate crystals. ## Storage Specimens should be stored exclusively in stable, sealed "micromount" boxes to protect them from mechanical damage, dust, and changes in humidity. Display should only be done under a microscope.

External references

Sources

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