Hydroscarbroite

Chemical formula: Al₁₄(CO₃)₃(OH)₃₆·nH₂O

Hydroscarbroite is a hydrated aluminum carbonate, occurring as soft, white masses with an earthy or chalky texture.

## Characteristics Hydroscarbroite is a rare, hydrated aluminum carbonate. It forms very fine-grained, soft, and porous aggregates resembling chalk or clay. It typically occurs as veins, crusts, or fissure fillings. Due to its microcrystalline structure, individual crystals are not visible to the naked eye. It is very light and soft to the touch. ## Physical Properties This mineral is characterized by very low hardness, approximately 2 on the Mohs scale, meaning it can be scratched with a fingernail. It has a dull or earthy luster and is translucent. Its density has not been precisely determined, but it is very low. ## Colors and Varieties Hydroscarbroite is usually white, sometimes with a creamy or grayish tint due to impurities. No distinct color varieties or commercial forms are recognized. ## History and Name The mineral's name refers to its chemical composition (hydroxyl groups and water - "hydro") and its discovery location - Scarborough, England. It was described as a new mineral in 1960, although the substance was previously known as "scarbroite." ## Uses Due to its rarity and unassuming appearance, hydroscarbroite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or minerals from specific localities.

Properties

Mohs hardness
2
Luster
Earthy
Streak
White
Density
0
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification Hydroscarbroite can be identified by its characteristic chalk-like or clay-like appearance, very low hardness (scratches with a fingernail), and white color. It is very light and often adheres to the tongue due to its porosity. It reacts violently with hydrochloric acid, which is a key feature distinguishing it from visually similar clay minerals. ## Distinguishing from Similar Minerals It can be confused with kaolinite, halloysite, or other clay minerals. It is distinguished from them by its violent reaction with acids (a characteristic of carbonates). It differs from calcite or dolomite by its extremely low hardness and earthy appearance. ## Crystal Forms This mineral forms exclusively cryptocrystalline or earthy aggregates. It does not occur in the form of well-developed, macroscopically visible crystals. It is most commonly found as veins and fillings in rock fissures.

Geological environment

## Genesis Hydroscarbroite is a secondary mineral. It forms in the weathering zone as a result of carbonate-rich waters interacting with aluminum-rich rocks, such as alum shales or sandstones. It forms under low temperature and pressure conditions. ## Mineral Associations It co-occurs with minerals such as gibbsite, halloysite, and also with sulfates, e.g., gypsum. ## Localities The most important and classic occurrence is South Bay in Scarborough, North Yorkshire, England, where it was discovered. It is also known from several other localities worldwide, including the Czech Republic and Hungary, but it is a rare mineral everywhere.

Rarity

Very rare

For collectors

## Quality Criteria The quality of a hydroscarbroite specimen is primarily assessed based on the purity and abundance of the material. Thick, pure white veins and fillings contrasting with the host rock are most valued. Since it does not form crystals, their shape is not a criterion for evaluation. A well-documented locality is important, especially if it is the type locality (Scarborough). ## Popular Localities By far the most sought-after and classic specimens come from the type locality in Scarborough, England. Material from other places is mainly of interest to systematic collectors.

Care and storage

## Cleaning Hydroscarbroite specimens are extremely delicate, soft, and porous. They should not be cleaned wet, as they can absorb water and disintegrate. Dust can be removed very carefully with a soft brush or a stream of compressed air from a distance. ## What to Avoid Avoid contact with water and any chemicals, especially acids, with which it reacts violently. The mineral is very soft, susceptible to scratching and abrasion. It should be protected from shocks, drops, and pressure. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from mechanical damage, dust, and moisture. Do not place other minerals on top of them.

External references

Sources

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