Jahnsite-(CaMnZn)

Chemical formula: CaMn<sup>2+</sup>Zn<sup>2+</sup><sub>2</sub>Fe<sup>3+</sup><sub>2</sub>(PO<sub>4</sub>)<sub>4</sub>(OH)<sub>2</sub>·8H<sub>2</sub>O

A rare hydrated phosphate from the jahnsite group, forming aggregates of small, tabular crystals with a characteristic orange-brown color.

## Characteristics Jahnsite-(CaMnZn) is a rare, hydrated phosphate mineral belonging to the jahnsite group. It occurs as aggregates of very small, thin, tabular crystals, rarely exceeding 1 mm in length. These crystals often form rosetted or radial aggregates, as well as coatings and crusts on other minerals. Its most characteristic visual feature is an intense orange-brown to yellow-brown color. ## Physical Properties This mineral is characterized by a hardness of approximately 4 on the Mohs scale. It has a vitreous luster and is transparent to translucent. The density of jahnsite-(CaMnZn) is about 3.01 g/cm³. ## Colors and Varieties Jahnsite-(CaMnZn) occurs in shades from orange-brown to yellow-brown. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 2004 by Anthony R. Kampf, Pete J. Dunn, George W. Robinson, Paul B. Moore, and Joseph J. Pluth. Its name refers to its belonging to the jahnsite group and to the dominant elements in its chemical composition: calcium (Ca), manganese (Mn), and zinc (Zn). The group name comes from Richard H. Jahns (1915-1983), a professor of geology at Stanford University, for his contributions to the mineralogy of granitic pegmatites. ## Uses Jahnsite-(CaMnZn) has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and micromounts.

Properties

Mohs hardness
4
Luster
Vitreous
Streak
Light brown
Density
3.01
Cleavage
Good on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Jahnsite-(CaMnZn) can be identified by its characteristic orange-brown color, vitreous luster, and typical occurrence in the form of small, tabular crystals forming rosetted or radial aggregates. Key to identification is its occurrence environment – oxidized zones of zinc deposits. ## Distinguishing from Similar Minerals It can be confused with other minerals from the jahnsite group or similar secondary phosphates. Final differentiation from other members of the jahnsite group (e.g., jahnsite-(CaMnMn) or jahnsite-(CaMnFe)) requires advanced chemical analyses (EDS/WDS) to determine the dominant cations. Visually, it is practically indistinguishable from other brown jahnsites. ## Crystal Forms Crystals are thin, tabular, flattened parallel to {010} and elongated along the [001] axis. They typically form fan-like, radial, or rosetted aggregates, as well as thin crusts.

Geological environment

## Genesis Jahnsite-(CaMnZn) is a secondary mineral, formed in the oxidation (weathering) zones of zinc ore deposits. It forms as a result of the alteration of earlier phosphate and sulfide minerals in the presence of solutions rich in zinc, manganese, iron, and phosphorus. ## Mineral Associations This mineral co-occurs with other secondary zinc and phosphate minerals. At the type locality (Broken Hill mine), it was found in association with scholzite, hopeite, tarbuttite, hydroxylapatite, rockbridgeite, phosphophyllite, and pyrite. ## Localities The most important and type locality for this mineral is the Broken Hill mine in New South Wales, Australia. This is the only confirmed and well-documented locality for jahnsite-(CaMnZn).

Rarity

Very rare

For collectors

## Quality Criteria The collector appeal of jahnsite-(CaMnZn) specimens depends on several factors. Most valued are specimens with well-formed, sharp crystals forming aesthetic, rosetted or fan-like aggregates. The intensity and saturation of the orange-brown color also increase value. Contrast with the host rock (matrix) and the presence of rare associated minerals are important. Due to the microscopic size of the crystals, specimens are almost exclusively the domain of micromount collectors. ## Popular Localities The only source of collector specimens is the historical type locality – the Broken Hill mine in Australia. Material from this location is extremely rare and sought after by specialized collectors.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its fragility and potential reactivity, avoid washing in water, and especially in chemical agents. If it is necessary to remove loose contaminants, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with acids and other chemicals that may damage or dissolve the mineral. Protect it from high temperatures, which can lead to dehydration and destruction of the crystal structure. Avoid ultrasonic cleaning devices. ## Storage As a brittle mineral occurring in the form of tiny crystals, jahnsite-(CaMnZn) should be stored in specialized "micromount" boxes that protect it from mechanical damage and dust. It should be kept in stable conditions, away from direct sunlight and heat sources.

Sources

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