Pumpellyite-(Mn^2+^)

Chemical formula: Ca<sub>2</sub>Mn<sup>2+</sup>Al<sub>2</sub>(SiO<sub>4</sub>)(Si<sub>2</sub>O<sub>7</sub>)(OH)<sub>2</sub>·H<sub>2</sub>O

A rare silicate from the pumpellyite group, distinguished by the dominance of manganese (Mn²⁺) and forming characteristic, fibrous aggregates ranging in color from pink to reddish-brown.

## Characteristics Pumpellyite-(Mn²⁺) is a mineral belonging to the pumpellyite group, in which manganese (Mn²⁺) is the dominant element in one of the sites in the crystal structure. It typically forms fibrous, radial, or spherulitic aggregates; less commonly, it occurs as poorly formed, tabular crystals. Its appearance is very characteristic – aggregates often resemble tiny needles or hairs gathered into spherical forms. ## Physical Properties This mineral is characterized by a hardness of approximately 6 on the Mohs scale. It has a vitreous, sometimes silky luster, especially visible on fibrous aggregates. It is a translucent to opaque mineral. Its density is approximately 3.43 g/cm³. ## Colors and Varieties Pumpellyite-(Mn²⁺) exhibits colors ranging from pink, through red, reddish-brown, to brown. The coloration is directly related to the presence of manganese. No named commercial or gemological varieties are distinguished. ## History and Name The mineral's name refers to its chemical composition – it is a member of the pumpellyite group with dominant divalent manganese (Mn²⁺). The pumpellyite group was named after the American geologist Raphael Pumpelly (1837-1923). The suffix "-(Mn²⁺)" was added in accordance with the mineral nomenclature rules of the International Mineralogical Association (IMA) to distinguish it from other members of the group, such as pumpellyite-(Mg) or pumpellyite-(Fe²⁺). ## Uses Pumpellyite-(Mn²⁺) has no industrial applications. It is solely a mineral of scientific and collecting interest, sought after for its rarity and attractive forms of occurrence.

Properties

Mohs hardness
6
Luster
Vitreous to silky
Streak
Pale pink to white
Density
3.43
Cleavage
Good on {001}, imperfect on {100}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Monoclinic

Diagnostic features

## Identification The key diagnostic feature is its form of occurrence – radial or spherical aggregates composed of fine, acicular or fibrous crystals. Its characteristic color, from pink to reddish-brown, and its co-occurrence with other manganese minerals are also distinctive. ## Distinguishing from Similar Minerals Pumpellyite-(Mn²⁺) can be confused with other fibrous minerals of similar color, such as inesite, rhodochrosite (in fibrous forms), or some zeolites. It differs from inesite often by a more reddish hue and hardness. It is distinguished from rhodochrosite by its lack of reaction with hydrochloric acid and higher hardness. Identification often requires advanced research methods, such as chemical analysis (EDS) or X-ray diffraction (XRD). ## Crystal Forms It most commonly occurs as fibrous, radial, spherulitic (spherical), and rosette aggregates. Single, well-formed crystals are extremely rare and appear as small, tabular prisms.

Geological environment

## Genesis It is a low-temperature hydrothermal mineral, forming in veins and fractures cutting manganese deposits that have undergone metamorphic processes. It forms under zeolite facies or prehnite-pumpellyite facies conditions. ## Mineral Associations It often co-occurs with other manganese minerals, such as braunite, hausmannite, rhodochrosite, pyroxmangite, as well as with quartz, calcite, barite, epidote, and zeolites. ## Localities The most important and well-known localities, from which the best collectible specimens originate, are in South Africa, in the N'Chwaning I, II, and III and Wessels mines in Hotazel, in the Kalahari Manganese Field. It is also known from several localities in Italy (Liguria), Japan (Oashi mine), and the USA (Washington and California states).

Rarity

Rare

For collectors

## Quality Criteria Specimens from the N'Chwaning mines in South Africa are most highly valued. An ideal collector's specimen should consist of well-formed, spherical or radial aggregates of intense, red or deep pink color. Aesthetic composition on the rock matrix, color contrast (e.g., red spheres on white calcite), and absence of damage to delicate fibers are important. The size of the aggregates also affects value – larger, well-formed spherulites are significantly more expensive. ## Popular Localities Specimens from the Kalahari Manganese Field in South Africa are by far the most sought after by collectors. Minerals from these localities have set the standard of quality for this species.

Care and storage

## Cleaning Specimens should be cleaned very carefully, preferably using a soft brush to remove dust. For heavier soiling, compressed air can be used. Contact with water, especially with chemicals, is not recommended due to the delicate, fibrous structure of the aggregates. ## What to Avoid Avoid ultrasonic and steam cleaners, which can irreversibly damage fragile aggregates. The mineral is sensitive to strong acids. It should not be heated or exposed to sudden temperature changes. ## Storage Collectible specimens of pumpellyite-(Mn²⁺) are brittle and susceptible to mechanical damage. It is best to store them in separate, padded boxes or display cases, away from harder minerals that could scratch them. They should be protected from dust and moisture.

Sources

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