Carbocalumite

Chemical formula: Ca<sub>4</sub>Al<sub>2</sub>(OH)<sub>12</sub>(CO<sub>3</sub>)·6H<sub>2</sub>O

A very rare hydrated calcium aluminum hydroxide carbonate, forming microscopic, colorless crystals in the form of hexagonal plates.

## Characteristics Carbocalumite is an extremely rare mineral from the hydroxycarbonate group. It occurs as very small, colorless, hexagonal, tabular crystals, usually not exceeding 0.1 mm in diameter. These crystals often form aggregates or thin coatings on the surface of other minerals. Due to its microscopic size, it is a mineral primarily of interest to specialized collectors and scientists. ## Physical properties Carbocalumite crystals exhibit a vitreous luster. Hardness and density have not been precisely determined due to the small size of the samples. It is transparent to translucent. ## History and name The mineral's name refers to its chemical composition: "carbo" refers to the presence of the carbonate group (CO₃), "cal" to calcium, and "um" to aluminum. It was approved as a new mineral by the International Mineralogical Association (IMA) in 2011 (IMA2011-067).

Properties

Luster
Vitreous
Streak
White
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of carbocalumite is possible almost exclusively using advanced analytical methods, such as X-ray diffraction (XRD) and chemical spectroscopy (EDS/WDS). Visual identification in the field is impossible. Its characteristic habit is in the form of microscopic, hexagonal plates. ## Distinguishing from similar minerals It can be confused with other secondary minerals from the hydrotalcite or ettringite group, which form similar white or colorless coatings. Certain differentiation requires specialized laboratory analysis. ## Crystal forms It forms exclusively very small, hexagonal, tabular crystals.

Geological environment

## Genesis Carbocalumite is a secondary mineral, formed as a result of low-temperature hydrothermal processes or weathering. It forms in voids and fissures within metamorphic rocks, such as skarns, formed at the contact of carbonate rocks with magmatic intrusions. ## Mineral associations It co-occurs with minerals such as ettringite, calcite, willemite, hydroxylellestadite, vesuvianite, grossular, and wollastonite. ## Localities The only known occurrence of this mineral (type locality) is the Wessels Mine in the Hotazel area, Kalahari Manganese Field, Republic of South Africa.

Rarity

Extremely rare

For collectors

## Quality criteria As a microscopic mineral, its collector's value is primarily determined by the abundance of its occurrence on the rock matrix and the good development and transparency of the microcrystals. The most desirable specimens are those where carbocalumite is clearly visible in association with other rare minerals from this locality.

Care and storage

## Cleaning Due to the extreme delicacy and microscopic size of the crystals, mechanical cleaning is inadvisable and can lead to the destruction of the specimen. Contact with water and chemicals should be avoided. ## What to avoid The mineral is unstable in contact with acids, which cause its rapid dissolution. It should be protected from moisture, high temperatures, and all chemicals. ## Storage Carbocalumite specimens should be stored exclusively in specialized, tightly sealed "micromount" containers, protecting them from dust, moisture, and mechanical damage.

Sources

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