Jeankempite

Chemical formula: Ca₅(As⁵⁺O₄)₂(As⁵⁺O₃OH)₂(H₂O)₇

Jeankempite is a very rare, hydrated calcium arsenate, forming colorless, tabular crystals with a pearly luster.

## Characteristics Jeankempite is a hydrated calcium arsenate, occurring as very small, colorless, tabular crystals, not exceeding 0.5 mm. It forms thin, bladed crystals gathered into small, radial aggregates or rosettes. Due to its small size, its visual features are difficult to observe without magnification. ## Physical Properties The crystals are flexible and can be bent. The mineral is characterized by a pearly luster on cleavage surfaces and a vitreous luster on other faces. It is transparent to translucent. Its Mohs hardness is approximately 2, and its density is slightly greater than 3 g/cm³. ## History and Name The mineral was approved by the IMA in 2016. Its name honors Jean Kemp (born 1940), a Belgian mineral collector who found the first specimens of this mineral. It was described by a team of mineralogists, including Stuart J. Mills, based on material from the Jote mine in Chile. ## Uses Jeankempite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals and a subject of scientific research.

Properties

Mohs hardness: 1.5
Color: Colorless to white
Luster: Pearly
Streak: White
Density: 2.92
Cleavage: At least one, on <mi>{01_1}</mi>
Fracture: Irregular/Uneven
Transparency: Transparent,Translucent
Crystal system: Triclinic

Diagnostic features

## Identification Amateur identification of jeankempite is practically impossible. It requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical spectroscopy (EDS), due to its occurrence as microscopic crystals and its co-occurrence with other similar arsenates. ## Distinguishing from Similar Minerals It can be confused with other secondary arsenates, such as pharmacolite, weilite, or haidingerite, which form similar colorless or white coatings and aggregates. Definitive differentiation is only possible based on chemical and crystallographic analysis. ## Crystal Forms Jeankempite forms very thin, tabular or bladed crystals, elongated along one axis and flattened. These crystals often combine into small, radial or fan-shaped aggregates and rosettes.

Geological environment

## Genesis It is a secondary mineral, formed in the oxidation zones (gossans) of ore deposits rich in arsenic. It forms as a result of the weathering of primary arsenic minerals, such as arsenopyrite, in a dry, desert climate. ## Mineral Associations At the type locality (Jote mine), it co-occurs with arsenopyrite, quartz, pyrite, chalcopyrite, as well as other secondary arsenates, such as pharmacolite, weilite, haidingerite, picropharmacolite, and sainfeldite. ## Localities The only confirmed locality of jeankempite in the world is its type locality – the Jote mine in the Tierra Amarilla district, Atacama Region, Chile.

Rarity

Extremely rare

For collectors

## Quality Criteria Due to its extreme rarity and microscopic size, the main criterion for a specimen's value is its unambiguous analytical identification. Most desirable are specimens where well-formed, even if tiny, crystal aggregates are visible, clearly standing out from the host rock. The richness of association with other rare arsenates also increases its scientific and collector's value.

Care and storage

## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to the extreme delicacy and small size of the crystals, any other method, including the use of water or brushes, risks destroying them. ## What to Avoid Avoid contact with water, chemicals, as well as any vibrations and impacts. The crystals are very brittle and flexible, but easily suffer permanent damage. Do not expose it to high temperatures, which can cause the loss of water from its structure. ## Storage Jeankempite specimens must be stored in stable conditions, preferably in sealed "micromount" containers, which protect them from mechanical damage, dust, and humidity changes. Avoid places exposed to shocks.