Giftgrubeite

Chemical formula: CaMn<sup>2+</sup><sub>2</sub>Ca<sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>2</sub>(As<sup>5+</sup>O<sub>3</sub>OH)<sub>2</sub>·4H<sub>2</sub>O

Giftgrubeite is a very rare, hydrated calcium manganese arsenate, forming microscopic, colorless to pale pink tabular crystals.

## Characteristics Giftgrubeite is a mineral from the arsenate group, occurring as very small, tabular or bladed crystals, rarely exceeding 0.2 mm in length. Crystals are usually colorless, sometimes with a pale pink or pale yellow tint. They form small, radial aggregates or rosettes on the surface of the host rock. Due to its microscopic size, it is a mineral primarily available to specialized collectors. ## Physical Properties Crystals exhibit a vitreous luster. Hardness and density have not been precisely measured due to the small size of samples, but the Mohs hardness is estimated to be around 3. The mineral is transparent to translucent. ## Colors and Varieties This mineral is typically colorless. Specimens with a very pale pink or yellowish coloration have also been observed. No named varieties are distinguished. ## History and Name Giftgrubeite was discovered in the historic silver and cobalt ore mine "Giftgrube" in the locality of Saint-Jacques (Sankt Ulrich) in the Val d'Anniviers valley in the canton of Valais, Switzerland. The mineral's name, approved in 2017, comes directly from the name of the type locality (the mine). The word "Giftgrube" in German literally means "poison mine" or "toxic mine," which refers to the high content of toxic arsenic in the ores extracted there. ## Uses Giftgrubeite has no industrial application. It is solely an object of scientific and collecting interest, sought after by collectors specializing in rare minerals or minerals from specific localities (so-called "micromounts").

Properties

Mohs hardness
3
Luster
Vitreous
Streak
White
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification Amateur identification of giftgrubeite is practically impossible. It requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD) combined with chemical analysis (EDS). In a collection, it is identified based on the label and its appearance under a microscope – characteristic, tiny, tabular crystals forming rosettes. ## Distinguishing from Similar Minerals It can be confused with many other secondary arsenates occurring in the same environment, such as pharmacolite, picropharmacolite, or sainfeldite, which can also form colorless or white coatings and aggregates. Definitive differentiation is only possible through laboratory analysis. ## Crystal Forms Giftgrubeite forms very small, thin, tabular crystals with a bladed habit, elongated along one axis. These crystals often combine into radial aggregates, fans, or small, spherical rosettes.

Geological environment

## Genesis Giftgrubeite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits rich in arsenic. It forms as a result of the reaction of arsenic-supersaturated solutions with minerals containing calcium and manganese, under low temperature and pressure conditions. It occurs in cavities and fissures of carbonate rocks (dolomites) within the deposit. ## Mineral Associations This mineral co-occurs with other arsenates, such as sainfeldite, picropharmacolite, pharmacolite, rösslerite, as well as with calcite, dolomite, and quartz. ## Localities The only confirmed occurrence of giftgrubeite in the world is its type locality – the historic "Giftgrube" mine in the Val d'Anniviers valley in Switzerland.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of a giftgrubeite specimen is primarily assessed based on the richness and aesthetics of the crystal aggregates visible under a microscope. Specimens with clearly formed, sharp crystals creating visually attractive rosettes or fans are most valued. Crystal size, although always microscopic, is also important – larger (up to 0.2 mm) and well-formed crystals are rated higher. Contrast with the color of the host rock can further enhance the specimen's appeal. ## Popular Localities The only source of giftgrubeite specimens is the Giftgrube mine in Switzerland, which makes every specimen from this locality valuable by definition.

Care and storage

## Cleaning Giftgrubeite specimens are extremely delicate and small. Any mechanical cleaning should be avoided. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust particles. Contact with water is not recommended due to the risk of damaging delicate crystals and potential chemical reactions. ## What to Avoid Contact with acids and other chemicals must be strictly avoided. The mineral is sensitive to shocks and abrasions. It should not be heated or exposed to prolonged moisture. ## Storage Giftgrubeite specimens, as typical "micromounts," should be stored exclusively in specialized, sealed perky boxes, which protect them from dust, moisture, and mechanical damage. Exposure to direct sunlight should be avoided.

Sources

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