Wickmanite

Chemical formula: Mn₂+Sn₄+(OH)₆

Wickmanite is a rare tin and manganese hydroxide, forming characteristic, octahedral crystals with a yellow to brown color.

## Characteristics Wickmanite is a mineral from the stottite group, belonging to the hydroxide class. It most often forms well-developed, octahedral or hexoctahedral crystals, usually reaching several millimeters in size. Less frequently, it occurs in granular or massive aggregates. Its appearance is distinctive due to its resinous or almost vitreous luster and intense, warm colors. ## Physical Properties The hardness of wickmanite on the Mohs scale is 3.5-4.5, making it a relatively soft mineral. It has a density of about 3.84 g/cm³, which is significant for a mineral with a non-metallic luster. It is brittle and exhibits good cleavage in one plane. Its crystals can range from transparent to translucent. ## Colors and Varieties This mineral ranges in color from light yellow, through orange-yellow, to reddish-brown and brown. Sometimes, color zoning is observed within individual crystals, which enhances their attractiveness. No named varieties are distinguished. ## History and Name Wickmanite was first described in 1967 by Paul B. Moore and Joseph V. Smith based on specimens found in the Långban mine in Sweden. The mineral is named in honor of Frans Erik Wickman (1915–2013), a Swedish mineralogist and geochemist at the Swedish Museum of Natural History in Stockholm, for his contributions to the study of Långban minerals. ## Uses Due to its rarity, wickmanite has no industrial applications. It is solely an object of scientific interest and a valuable collector's stone.

Properties

Mohs hardness: 3.5-4.5
Luster: Resinous to Vitreous
Streak: White
Density: 3.84
Cleavage: Good on {001}
Fracture: Conchoidal to uneven
Transparency: Transparent to Translucent
Crystal system: Cubic

Diagnostic features

## Identification The most important diagnostic feature of wickmanite is its crystallographic form – regular, sharp octahedra. Other helpful identification features include: resinous luster, yellow to brown color, relatively high density, and co-occurrence with other rare tin and manganese minerals. The streak is always white. ## Distinguishing from Similar Minerals Wickmanite can be confused with sphalerite, which, however, has excellent cleavage in several directions and a different crystal habit. Scheelite is much denser and often exhibits strong fluorescence under UV light, which wickmanite does not. Reliable differentiation from other rare minerals of the stottite group (e.g., stottite, tetrawickmanite) is usually only possible using advanced analytical methods, such as Raman spectroscopy or chemical analysis. ## Crystal Forms The dominant form is octahedra {111}, often with sharp edges and smooth faces. Sometimes, small cube faces {100} appear on them, forming transitional forms (hexoctahedra). It also occurs in granular aggregates and crusts.

Geological environment

## Genesis Wickmanite is a rare secondary mineral. It forms in the oxidation zones of tin and manganese deposits, most often within skarns or complex granitic pegmatites. It forms as a result of hydrothermal alteration or weathering of primary tin-bearing minerals in a manganese-rich environment. ## Mineral Associations This mineral often occurs in association with other rare minerals, which is a clue in its search. Its typical associations include: stottite, tetrawickmanite, jeanbandyite, schoenfliesite, natanite, as well as Långban minerals such as pinakiolite, katoptrite, and tephroite. ## Localities The most important and historical locality for wickmanite is the Långban mine in the Värmland region of Sweden, from which the world's best specimens originate. It is also known from several other localities, including the Tsumeb mine in Namibia, the Paddy's River mine in Australia, and Franklin, New Jersey, USA.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized wickmanite specimens are those with sharp, well-formed, and fully transparent crystals of intense yellow or orange color. Crystal size is very important – those exceeding 5 mm are considered exceptional. Specimens on matrix, especially in association with other rare minerals, are more desirable than single, loose crystals. ## Popular Localities By far the most sought-after by collectors are classic specimens from the discovery locality – Långban in Sweden. They are characterized by exemplary crystal development. Specimens from Tsumeb in Namibia are also valued, although they often have a slightly different appearance and mineral association.

Care and storage

## Cleaning Wickmanite specimens should be cleaned very carefully due to their low hardness. It is best to use a soft brush to remove dust. If necessary, the specimen can be rinsed in distilled water and then thoroughly dried. Ultrasonic cleaners should be avoided, as they can cause cracks. ## What to Avoid The mineral is sensitive to acids. It should be protected from contact with household and laboratory chemicals. As a relatively soft mineral, it is susceptible to scratching by harder minerals (e.g., quartz). It is recommended to avoid sudden temperature changes and prolonged exposure to direct sunlight. ## Storage Collector's specimens of wickmanite are best stored in separate, padded boxes (such as "membrane boxes" or display cases) to prevent abrasion and scratching. When on display, ensure it is in a stable location, away from vibrations and the risk of falling.

Sources

IMA Mineral List (CNMNC)