Kottenheimite

Chemical formula: Ca<sub>3</sub>Si(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>·12H<sub>2</sub>O

Kottenheimite is a very rare calcium sulfate and silicate, forming microscopic, colorless crystals in gas vesicles of volcanic rocks.

## Characteristics Kottenheimite is a sulfate mineral belonging to the ettringite group. It occurs as very small, hexagonal, prismatic or acicular crystals, rarely exceeding 0.2 mm in length. The crystals are colorless and transparent, with a vitreous luster. They typically form small, radial aggregates or disordered clusters on the walls of vesicles in volcanic rocks. Due to its microscopic size, it is a mineral of interest mainly to specialized collectors (micromounts). ## Physical Properties The hardness of kottenheimite has not been precisely determined, but it is estimated to be around 2.5 on the Mohs scale, similar to other minerals in its group. It is a brittle mineral. The calculated density is 1.96 g/cm³. The crystals exhibit a vitreous luster. ## Colors and Varieties This mineral is colorless. No colored varieties or trade names are known. ## History and Name Kottenheimite was discovered in 2011 in samples from a quarry in Kottenheim in the Eifel Mountains, Germany. Its name is derived directly from its type locality. It was approved by the International Mineralogical Association (IMA) in the same year under number 2011-042. It was described by Christian L. Lenz and co-workers. ## Applications Kottenheimite has no industrial or commercial use. Its significance is purely scientific and for collectors, as a very rare mineralogical species.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
White
Density
1.96
Cleavage
Perfect on {1010}
Fracture
Brittle
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of kottenheimite is possible almost exclusively using advanced analytical methods, such as Raman spectroscopy or chemical analysis by electron microprobe (EDS/WDS). Visually, under magnification, characteristic small, hexagonal, prismatic crystals can be observed. Reaction to water (solubility) can be an indication, but this is a destructive test. ## Differentiation from Similar Minerals Kottenheimite is visually almost identical to other minerals from the ettringite group, such as ettringite itself, thaumasite, or sturmanite, which often co-occur in the same environment. Definitive differentiation requires specialized laboratory tests. ## Crystal Forms Kottenheimite crystals have the form of hexagonal prisms or needles, often terminated by flat pinacoids. They usually form radial or tangled aggregates, and also grow individually on other minerals.

Geological environment

## Genesis Kottenheimite is a secondary mineral, formed under low-temperature hydrothermal processes. It forms in gas vesicles (geodes) within volcanic rocks, such as phonolites and leucitites. Its formation is associated with the interaction of sulfate-rich solutions with earlier silicate minerals in the presence of calcium. ## Mineral Associations This mineral co-occurs with other rare secondary minerals found in the vesicles of volcanic rocks in the Eifel region. The most common associations include: thaumasite, ettringite, gypsum, calcite, aragonite, willhendersonite, and apophyllite. ## Localities The only confirmed occurrence of kottenheimite in the world is its type locality: a quarry in Kottenheim, in the Bellerberg volcanic complex, in the Eifel Mountains, Rhineland-Palatinate, Germany.

Rarity

Extremely rare

For collectors

## Quality Criteria For micromount collectors, the most important quality criteria are: the sharpness and development of the crystals, their transparency, and their aesthetic arrangement on the rock matrix. Specimens with well-defined, individual crystals or attractive, radial aggregates are highly valued. Contrast with associated minerals also enhances the visual appeal of the specimen. ## Popular Localities All known specimens of kottenheimite come from a single location in the world – the quarry in Kottenheim, Germany. This is the classic and sole locality for this mineral, making it extremely important for collectors specializing in systematic minerals and rare species.

Care and storage

## Cleaning Kottenheimite specimens are extremely delicate and small. Mechanical or chemical cleaning is not recommended. If absolutely necessary, compressed air can be used from a safe distance to remove loose dust particles. Avoid contact with water, which can damage or dissolve the mineral. ## What to Avoid Absolutely avoid contact with water and all chemicals, including acids and detergents. The mineral is sensitive to changes in humidity and temperature. It should not be heated or exposed to direct sunlight. ## Storage Kottenheimite specimens, as micromounts, should be stored exclusively in sealed, lockable "micromount boxes" that protect them from dust, mechanical damage, and humidity changes. The box should be properly labeled.

Sources

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