Donbassite

Chemical formula: Al₂(Si₃Al)O₁₀(OH)₂·Al₂.₃₃(OH)₆

Donbassite is a rare, white or colorless mineral from the chlorite group, forming small, scaly aggregates, found in hydrothermal veins.

## Characteristics Donbassite is a mineral belonging to the chlorite group, closely related to cookeite and sudoite. It usually occurs as very fine, scaly or platy crystals that form compact, soft, and flexible aggregates. It is rarely observed in the form of distinct, hexagonal crystals. Its appearance is inconspicuous, most often resembling massive or earthy aggregates of talc or kaolinite. ## Physical Properties This mineral is characterized by a low hardness of 2-2.5 on the Mohs scale, which means it is very soft and can be scratched with a fingernail. It has a pearly luster on cleavage surfaces and a dull or earthy luster in compact aggregates. It is translucent to opaque. Its density is approximately 2.61 g/cm³. ## Colors and Varieties Donbassite is most often white, silvery-white, grayish-white, or yellowish. It can also be colorless. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1940 by E. K. Lazarenko, comes from its first discovery location – the Donets Coal Basin (Donbas) in Ukraine. It was discovered there in quartz-carbonate veins cutting through clay shales. ## Uses Donbassite has no industrial significance. It is solely an object of interest for collectors specializing in rare minerals or clay minerals, as well as a subject of scientific research.

Properties

Mohs hardness: 2-2.5
Color: White, light green
Luster: Pearly
Streak: White
Density: 2.63
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Donbassite is difficult to identify visually without specialized tests. Its key features include very low hardness (soft, can be scratched with a fingernail), pearly luster on cleavage planes, and occurrence in the form of finely scaly, flexible aggregates. It often has a "soapy" or "greasy" feel. ## Distinguishing from Similar Minerals It can be easily confused with other white clay minerals, such as kaolinite, dickite, and especially with other chlorites (e.g., cookeite) or talc. Talc is equally soft but usually more "soapy" to the touch. Kaolinite forms more compact, earthy masses. Final differentiation from similar minerals in the chlorite and kaolinite groups requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms microscopic, pseudohexagonal, tabular or platy crystals. Most often, it occurs as radial, spherulitic, or compact, finely scaly aggregates.

Geological environment

## Genesis Donbassite is a low-temperature hydrothermal mineral. It forms as a result of metasomatism of aluminosilicates in sedimentary rocks, especially in clay and carbonaceous shales. It can also crystallize in voids and fractures in quartz-carbonate veins. ## Mineral Associations It often co-occurs with minerals such as quartz, calcite, dolomite, ankerite, dickite, kaolinite, as well as sulfides (pyrite, chalcopyrite). ## Localities The most important localities for this mineral include the Donets Coal Basin in Ukraine (type locality). It is also found in zinc ore mines in the Olkusz region of Poland, in several localities in Arkansas (USA), in coal mines in Japan (e.g., Arakawa), and in Kazakhstan.

Rarity

Rare

For collectors

## Quality Criteria As a rare and usually unshowy mineral, donbassite is valued primarily for its documented occurrence. The most desired specimens by specialized collectors are those with well-visible, radial or spherulitic crystal aggregates, as well as those from the type locality (Donbas). Contrasting associations with other minerals, e.g., with quartz or sulfides, enhance the attractiveness of the specimen. ## Popular Localities The most classic and historically important specimens come from Donbas in Ukraine. For collectors in Poland, specimens from the Olkusz region have some value. Material from Arkansas, USA, is also found on the international market.

Care and storage

## Cleaning Donbassite specimens are very soft and delicate. They should be cleaned only very carefully, using a soft brush to remove dust. Due to its potential reactivity with water, wet cleaning should be avoided, and if absolutely necessary, distilled water should be used, and the specimen dried immediately. ## What to Avoid Contact with water, acids, and other chemicals should be avoided. The mineral is very soft, so it must be protected from scratching and impacts. It should not be heated or exposed to prolonged moisture. ## Storage It is recommended to store donbassite specimens in closed, dry containers or display cases, away from dust and moisture. It is best to keep it in a separate compartment to avoid contact with harder minerals that could damage it.