Aluminotschermakite

Chemical formula: &#9744;Ca<sub>2</sub>(Mg<sub>3</sub>Al<sub>2</sub>)(Si<sub>6</sub>Al<sub>2</sub>)O<sub>22</sub>(OH)<sub>2</sub>

Aluminotschermakite is a rare amphibole group mineral, an aluminum analogue of tschermakite, found in metamorphic rocks.

## Characteristics Aluminotschermakite is a silicate group mineral belonging to the amphiboles. It is the aluminum (Al) analogue of tschermakite, forming an isomorphic series with it. It usually occurs in fibrous, radial, columnar, or granular aggregates. Well-formed, individual crystals are extremely rare and appear as short prisms. ## Physical Properties This mineral is characterized by a hardness of 5-6 on the Mohs scale. It has a vitreous luster and a density of approximately 3.16 g/cm³. It is translucent to nearly opaque. ## Colors and Varieties Aluminotschermakite is most often dark green, greenish-black, or black. No distinct color or commercial varieties are recognized for it. Its chemical composition may vary slightly depending on the content of magnesium, iron, and aluminum. ## History and Name The mineral's name refers to its chemical composition – high aluminum content (Alumino-) – and its relation to tschermakite. Tschermakite, in turn, was named after Gustav Tschermak von Seysenegg (1836-1927), an Austrian mineralogist and petrographer who made significant contributions to the study of amphiboles and pyroxenes. Aluminotschermakite is an IMA-approved end-member mineral in its series. ## Uses Due to its rare occurrence in well-formed specimens, aluminotschermakite has no industrial application. It is primarily of scientific importance as an indicator of metamorphic conditions, and of collector's interest for specialized collectors of rock-forming minerals.

Properties

Mohs hardness
5-6
Luster
Vitreous
Streak
Greenish white
Density
ok. 3.16
Cleavage
Perfect on {110}
Fracture
Uneven
Transparency
Translucent to Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identifying aluminotschermakite based on visual characteristics is practically impossible. Its appearance does not differ from common hornblende and other dark amphiboles. A key feature of the amphibole group is perfect cleavage in two directions, intersecting at angles of approximately 56° and 124°, visible in cross-sections of crystals. ## Distinguishing from Similar Minerals It can be confused with numerous minerals from the amphibole group, such as hornblende, pargasite, or ferrohornblende. Definitive differentiation requires advanced analytical methods, such as electron microprobe analysis (EMPA) or X-ray diffraction (XRD), which allow for precise determination of chemical composition. ## Crystal Forms It most often forms fibrous, columnar, radial, or granular aggregates in rock. Individual, well-formed crystals with a habit of short, thick columns (prisms) are rarely found.

Geological environment

## Genesis This is a typical mineral of metamorphic rocks that have undergone transformations under medium and high pressure and temperature conditions. It forms in the amphibolite and eclogite facies. ## Mineral Associations It co-occurs with other metamorphic rock minerals, such as garnet (especially pyrope and almandine), omphacite, diopside, plagioclase, epidote, zoisite, and other amphiboles (e.g., pargasite). ## Localities As a rock-forming mineral, it is a component of rocks in many metamorphic massifs worldwide. Confirmed occurrences include Austria (Saualpe, Koralpe), Czech Republic (Gföhl massif), Italy (Val d’Ala), Norway, and the United States. However, these are not localities that provide specimens of commercial significance.

Rarity

Rare

For collectors

## Quality Criteria Aluminotschermakite is a mineral of interest mainly to systematic collectors and scientific institutions. The value of a specimen is determined not by its aesthetics, but by the purity of the material, the possibility of its unambiguous identification, and its co-occurrence with other rare metamorphic minerals. Well-formed crystals, even small ones, are highly prized due to their rarity. ## Popular Localities There are no popular localities in a commercial sense. Material for research and systematic collections comes from various metamorphic localities worldwide where petrological studies are conducted.

Care and storage

## Cleaning Aluminotschermakite specimens should be cleaned carefully, using a soft brush and distilled water. For delicate, fibrous aggregates, avoid strong water jets and ultrasonic cleaners, which can damage the specimen's structure. ## What to Avoid The mineral is sensitive to strong acids. However, it is stable under normal conditions and shows no sensitivity to sunlight or temperature changes under household conditions. ## Storage Store under standard conditions, protecting from dust and mechanical damage. It does not require special climatic conditions. Fibrous specimens should be stored in closed boxes to prevent crumbling.

Sources

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