Alumino-oxy-rossmanite

Chemical formula: Al<sub>3</sub>Al<sub>6</sub>(Si<sub>5</sub>AlO<sub>18</sub>)(BO<sub>3</sub>)<sub>3</sub>(OH)<sub>3</sub>O

An extremely rare mineral from the tourmaline group, distinguished by its unique chemical composition with dominant aluminum and oxygen.

## Characteristics Alumino-oxy-rossmanite is a mineral belonging to the tourmaline supergroup. It has been identified as small, anhedral (not exhibiting its own crystallographic forms) zones within elbaite crystals. Due to the microscopic size of its occurrences, its visual features are not observed on a macroscopic scale. ## Physical Properties The mineral's hardness is 7.5 on the Mohs scale, and its density is calculated at 3.165 g/cm³. It has a vitreous luster and is transparent to translucent. ## Colors and Varieties In the type material, a pale blue to colorless hue was observed. No varieties of this mineral are distinguished. ## History and Name The mineral was officially approved by the International Mineralogical Association (IMA) in 2020 (IMA2020-035). Its name refers to its chemical composition – the dominance of aluminum (Alumino-) and oxygen (-oxy-) in specific positions in the crystal structure – and its relationship to another tourmaline group mineral, rossmanite. It was discovered by a team of mineralogists led by Jan Cempírek.

Properties

Mohs hardness
7.5
Luster
Vitreous
Streak
White
Density
3.165
Cleavage
Indistinct
Fracture
Uneven to conchoidal
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of alumino-oxy-rossmanite is impossible based on visual characteristics. It requires the use of advanced analytical techniques, such as electron microprobe analysis (EMPA-WDS) for precise chemical composition determination and single-crystal X-ray diffraction (SCXRD) for structural analysis. ## Distinguishing from similar minerals It is visually indistinguishable from other light-colored tourmalines, such as elbaite, olenite, or rossmanite. The differences are purely chemical and structural. ## Crystal forms It occurs as anhedral (allotriomorphic) zones or domains up to several hundred micrometers in size within elbaite crystals. It has not been observed in the form of independent, well-formed crystals.

Geological environment

## Genesis It forms in the final stages of crystallization in complex LCT-type (lithium, cesium, tantalum-rich) granitic pegmatites. It is a product of hydrothermal processes occurring in pegmatites. ## Mineral associations It co-occurs with elbaite, quartz, albite, and lepidolite. ## Localities The only confirmed locality in the world (type locality) is the pegmatite in Mirošov near Strážek in Moravia, Czech Republic.

Rarity

Extremely rare

For collectors

## Quality criteria The value of a specimen is not assessed based on typical aesthetic criteria, such as color or form. The only criterion is scientific confirmation of the presence of alumino-oxy-rossmanite in the sample (usually within elbaite), documented by appropriate analysis. ## Popular localities Specimens originate exclusively from the type locality in the Czech Republic and are mainly found in the collections of scientific institutions. The mineral is not available on the commercial collector's market.

Care and storage

## Cleaning Specimens, which are typically fragments of other minerals with microscopic inclusions, do not require specialized cleaning. If necessary, a soft brush and distilled water can be used. Ultrasonic cleaners should be avoided. ## What to avoid Like other tourmalines, it is sensitive to rapid temperature changes and thermal shock, which can cause cracks. Contact with strong acids, especially hydrofluoric acid, should be avoided. ## Storage Standard mineralogical collection storage conditions are sufficient – protection from dust, direct sunlight, and extreme temperatures.

Sources

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