Kochsándorite

Chemical formula: CaAl<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>4</sub>·H<sub>2</sub>O

A rare arsenate-sulfate of calcium and aluminum, forming characteristic spherical aggregates of white, bladed crystals.

## Characteristics Kochsándorite is a hydrated arsenate-sulfate of aluminum and calcium, most commonly occurring as characteristic, spherical aggregates up to several millimeters in diameter. These spheres are composed of radially arranged, tiny crystals with a bladed or platy habit. Individual crystals are usually too small to be seen with the naked eye, and their clusters have a delicate, fibrous texture. ## Physical Properties This mineral is very soft, with a Mohs hardness of about 2, meaning it can be scratched with a fingernail. It is also quite light. The crystals exhibit a pearly luster on cleavage surfaces and a vitreous luster on other faces. It is a translucent mineral. ## Colors and Varieties Kochsándorite is typically colorless or white. No colored varieties or trade names are known. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2005. Its name honors the Hungarian mineralogist and professor Sándor Koch (1896–1983) from the University of Szeged, in recognition of his contribution to the mineralogy of Hungary. ## Applications Due to its rarity and small size, kochsándorite has no industrial applications. It is solely an object of interest for collectors and scientists.

Properties

Mohs hardness
2
Luster
Pearly
Streak
White
Density
2.45
Cleavage
Perfect on {010}
Transparency
Translucent
Crystal system
Triclinic

Diagnostic features

## Identification The most important diagnostic feature of kochsándorite is its characteristic, white, spherical aggregates with a radial internal structure. Its very low hardness (approx. 2 on the Mohs scale), pearly luster, and occurrence in paragenesis with other arsenates are key for identification. ## Distinguishing from Similar Minerals It can be confused with other secondary minerals forming similar spherical aggregates, such as wavellite or some zeolites. However, kochsándorite is much softer than these. Its chemical composition (presence of arsenic and sulfur) also distinguishes it from wavellite. Definitive differentiation often requires advanced analytical methods, such as X-ray powder diffraction (XRD). ## Crystal Forms It forms spherical or hemispherical aggregates, which are composed of radially diverging bladed or thin-tabular crystals. Single, well-formed crystals are extremely rare and microscopic in size.

Geological environment

## Genesis Kochsándorite is a secondary mineral, formed in the oxidation zones of polymetallic deposits rich in arsenic. It forms as a result of the weathering of primary ore minerals in post-mining environments, often on dumps and in old workings. ## Mineral Associations This mineral occurs in association with other secondary arsenates and sulfates. It is most commonly found in paragenesis with gypsum, realgar, orpiment, arsenolite, and also with clay minerals. ## Localities It is an extremely rare mineral, known from very few localities worldwide. The type locality (place of first discovery) is the dump of the former Alsó-Rózsa mine in Nagybörzsöny, in the Börzsöny Mountains, Hungary. This locality remains the main source of the best specimens of this mineral.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued specimens are those with well-formed, spherical aggregates at least several millimeters in diameter. The intact, spherical shape of the clusters, their purity (snow-white color), and contrast with the rock matrix are important. Specimens showing numerous, densely packed spheres are particularly sought after. ## Popular Localities The only significant locality from a collector's point of view is the type locality in Nagybörzsöny, Hungary. Specimens from this location are the standard against which other finds are compared.

Care and storage

## Cleaning Kochsándorite specimens are extremely delicate and fragile. They should only be dry-cleaned using a soft brush to remove dust. Due to its low hardness and potential reactivity, contact with water and any chemical agents should be avoided. ## What to Avoid This mineral is sensitive to heat, which can cause the loss of structural water and its destruction. Ultrasonic cleaners, strong air currents, acids, and detergents should be avoided. Specimens should be protected from direct sunlight and high temperatures. ## Storage It is recommended to store specimens in stable conditions, in closed, padded boxes, to protect them from mechanical damage, dust, and sudden temperature changes. It should not be stored near heat sources.

Sources

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