Okruschite

Chemical formula: Ca₂Mn₂+₅Be₄(As₅+O₄)₆(OH)₄·₆H₂O

Okruschite is a very rare beryllium, calcium, and manganese arsenate, forming characteristic, radiating aggregates with a silky luster.

## Characteristics Okruschite is a hydrated beryllium, calcium, and manganese arsenate, belonging to the group of rare secondary minerals. It occurs as acicular or bladed crystals, which almost always form radiating, spherical, or hemispherical aggregates. Individual crystals within aggregates can reach up to 2 mm in length. Due to its delicate structure, okruschite specimens are brittle. ## Physical Properties This mineral is characterized by a hardness of 3 on the Mohs scale. Its luster is described as silky, which is typical for minerals with a fibrous structure. It is translucent. The calculated density is 3.19 g/cm³. ## Colors and Varieties Okruschite occurs in shades from pale yellow to yellowish-white. No varieties have been distinguished. ## History and Name The mineral was discovered in the dumps of the historic iron and manganese ore mine Glücksstern in Gottlob, in the Fichtelgebirge mountains (Bavaria, Germany). It was approved by the International Mineralogical Association (IMA) in 2013. The name honors Martin Okrusch (born 1934), a German mineralogist and petrologist, professor at the University of Würzburg, for his contributions to the study of the geology and mineralogy of northern Bavaria, including the Fichtelgebirge region.

Properties

Mohs hardness: 3
Luster: Silky
Streak: White
Density: 3.19
Cleavage: Good on {010}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification The key diagnostic feature of okruschite is its mode of occurrence: almost exclusively radiating, spherical aggregates composed of fine, acicular crystals. Its characteristic silky luster, pale yellow color, and occurrence in paragenesis with other rare arsenates are also distinctive. ## Distinguishing from Similar Minerals It can be confused with other minerals with a fibrous habit and radiating aggregates, such as wavellite or some zeolites. Differentiation requires chemical analysis (EDS/WDS) to confirm the presence of calcium, manganese, beryllium, and arsenic. The geological context (co-occurrence with other manganese arsenates) is also an important clue. ## Crystal Forms Crystals are elongated, acicular or bladed, flattened parallel to the {010} plane. They always occur as radiating, spherulitic aggregates.

Geological environment

## Genesis Okruschite is a secondary mineral, formed by hydrothermal processes or weathering within manganese and iron ore deposits that also contain beryllium. At the type locality (Gottlob), it formed under low-temperature hydrothermal conditions in quartzite fissures containing hausmannite and braunite. ## Mineral Associations This mineral co-occurs with other, often rare, minerals. At the type locality, it was found in association with kolfanite, hausmannite, braunite, quartz, barite, hematite, svabite, and flinkite. ## Localities The only confirmed locality for okruschite worldwide is its type locality: the historic Glücksstern mine in Gottlob, near Tröstau in the Fichtelgebirge mountains, Upper Franconia, Bavaria, Germany.

Rarity

Extremely rare

For collectors

## Quality Criteria The most prized specimens are those with well-formed, complete, and undamaged spherical aggregates, clearly distinct from the matrix. The size of the aggregates and the intensity of the color also influence the attractiveness of the specimen. Due to its extreme rarity, any fragment, even a small one, with visible aggregates is valuable. ## Popular Localities The only source of specimens is the Glücksstern mine in Germany. Collector material is extremely difficult to obtain and appears on the market very sporadically, usually coming from old collections or from local prospectors specializing in the mineralogy of this region.

Care and storage

## Cleaning Okruschite specimens are extremely delicate and brittle. Mechanical cleaning, including the use of brushes, should be avoided. If cleaning is absolutely necessary, compressed air can be carefully used from a safe distance to remove loose dust. Contact with water is not recommended due to possible solubility and the fragility of the aggregates. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. The mineral is sensitive to shocks and impacts – radiating aggregates can easily disintegrate. It should not be exposed to high temperatures. ## Storage Specimens should be stored in stable, padded collector boxes that protect against vibrations, dust, and mechanical damage. It is not suitable for display in open showcases where it is exposed to touch or dust.

Sources

IMA Mineral List (CNMNC)