Jahnsite-(MnMnZn)

Chemical formula: Mn²⁺Mn²⁺Zn²⁺₂Fe³⁺₂(PO₄)₄(OH)₂·8H₂O

Jahnsite-(MnMnZn) is a rare, hydrated phosphate of zinc, manganese, and iron, forming small, tabular crystals of an amber color.

## Characteristics Jahnsite-(MnMnZn) is a complex, hydrated phosphate mineral from the jahnsite group. It occurs as very small, tabular or bladed crystals, rarely exceeding 1 mm in length. These crystals often form radial aggregates, rosettes, or fan-like clusters. Due to their small size, its macroscopic features are difficult to observe without magnification. ## Physical Properties The mineral is characterized by a hardness of approximately 4 on the Mohs scale and a vitreous luster. It is transparent to translucent. The calculated density is about 3.25 g/cm³. It exhibits perfect cleavage in one direction. ## Colors and Varieties Jahnsite-(MnMnZn) has a characteristic amber-brown to orange-brown color. No color varieties or commercial varieties are known. ## History and Name As a member of the jahnsite group, its name honors American mineralogist and geologist Richard H. Jahns (1915-1983). The suffix "(MnMnZn)" specifies the occupation of particular positions in the crystal structure by manganese and zinc ions, according to the group's nomenclature. The mineral was described and approved by the IMA in 2004 (IMA2004-031). ## Uses Jahnsite-(MnMnZn) has no industrial applications. It is solely an object of interest for collectors specializing in rare phosphate minerals and micromounts.

Properties

Mohs hardness
4
Color
light golden brown
Luster
Vitreous
Streak
white
Density
2.89
Cleavage
parallel to {001}
Fracture
Irregular/Uneven,Splintery
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of jahnsite-(MnMnZn) under amateur conditions is practically impossible and requires advanced analytical methods, such as Raman spectroscopy or chemical analysis (EDS/WDS). Preliminary identification is based on its characteristic amber color, tabular crystal habit, radial aggregates, and co-occurrence with other rare phosphates in pegmatites. ## Distinguishing from Similar Minerals It can be confused with other minerals from the jahnsite group or visually similar phosphates, such as strengite or rockbridgeite. Definitive differentiation is only possible based on chemical composition analysis, which allows for the determination of the dominant cations in the structure. ## Crystal Forms It forms thin, tabular crystals with a bladed habit, elongated along the c-axis. These crystals almost always occur as radial or fan-like aggregates and rosettes.

Geological environment

## Genesis Jahnsite-(MnMnZn) is a secondary mineral, forming in the oxidation zones of ore deposits or as a result of hydrothermal processes affecting primary phosphates (e.g., triplite) in granitic pegmatites. It crystallizes in rock cavities and fissures. ## Mineral Associations It most commonly co-occurs with quartz, strengite, rockbridgeite, hureaulite, tavorite, barbosalite, as well as other minerals from the jahnsite group. ## Localities The most important and type locality (località tipo) for this mineral is the Tip Top mine in Custer County, South Dakota, USA. This is the only confirmed and well-documented locality for this specific member of the jahnsite group.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of jahnsite-(MnMnZn) specimens primarily depends on the quality and development of crystals within aggregates. Specimens with distinct, sharp, well-formed crystals creating aesthetic rosettes or fans are most valued. The intensity and purity of the amber color also increase the specimen's value. Contrast with the matrix mineral is an additional advantage. ## Popular Localities The only source of collector specimens is the Tip Top mine in South Dakota, USA. All specimens available on the market originate from this single locality.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using only a soft brush to remove dust. Due to its fragility and potential reactivity, contact with water and any chemical agents should be avoided. ## What to Avoid Avoid ultrasonic cleaners, strong water jets, acids, detergents, and solvents. The mineral is sensitive to high temperatures, which can lead to its dehydration and destruction of its structure. It should be protected from direct sunlight. ## Storage It is recommended to store specimens in stable conditions, in a dry place, away from heat and light sources. The safest form of display is a specialized micromount box, which protects delicate crystals from mechanical damage and dust.

External references

Sources

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