Tetrawickmanite

Chemical formula: Mn₂+Sn₄+(OH)₆

Tetrawikmanite is a rare mineral from the hydroxide group, being a manganese tin hydroxide, forming small, octahedral crystals.

## Characteristics Tetrawikmanite is a rare mineral belonging to the stottite group, chemically classified as a manganese tin hydroxide. It occurs as small, well-formed, octahedral crystals, rarely exceeding 1 mm in size. Crystals are most often overgrown on the surface of other minerals or found in small vugs. Due to its composition and structure, it is related to other minerals from the stottite group, such as wikmanite. ## Physical Properties This mineral is characterized by a hardness ranging from 3.5-4.5 on the Mohs scale. It has a vitreous, and sometimes adamantine luster on crystal faces. It is transparent to translucent. Its density is relatively high, approximately 3.96 g/cm³. ## Colors and Varieties Tetrawikmanite occurs in various shades of yellow - from light yellow, through yellowish-orange, to brownish-yellow. No specific color varieties or commercial names have been distinguished. ## History and Name The name "tetrawikmanite" refers to its tetragonal crystallographic system and its relationship to the structurally similar, monoclinic mineral - wikmanite. It was first described in 1971 by J. S. White Jr. and J. A. Nelen based on material from the Långban mine in Sweden, which is its type locality.

Properties

Mohs hardness: 3.5-4.5
Luster: Vitreous to adamantine
Streak: Light yellow
Density: 3.96
Cleavage: Imperfect on {011}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Tetrawikmanite is primarily identified by its characteristic crystal form - small, sharply terminated, tetragonal dipyramids, which resemble octahedra. Its yellow to orange color, vitreous luster, and occurrence in a specific geological environment (skarns) are key identification features. However, definitive confirmation requires advanced methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other minerals from the stottite group, especially with monoclinic wikmanite, which has an identical chemical composition (it is its polymorph). Distinguishing these two minerals is almost exclusively possible through crystallographic analysis. It can also be confused with other fine-grained, yellow minerals found in skarns, such as some garnets. ## Crystal Forms Tetrawikmanite crystals have the form of tetragonal dipyramids, which strongly resemble regular octahedra. They are usually single, well-formed crystals up to 1 mm in size, overgrown on other minerals.

Geological environment

## Genesis Tetrawikmanite is a mineral of metamorphic origin. It forms in skarn deposits that have undergone contact metamorphism. It forms in calcite veins cutting through manganese and iron ore deposits. ## Mineral Associations This mineral co-occurs with other minerals typical of this environment, such as calcite, baryte, cuprosklodowskite, fluorapophyllite-(K), hematite, and other rare manganese minerals. ## Localities The most important and classic locality for tetrawikmanite is its type locality - the Långban mine in the Värmland region of Sweden. This is a historic site known for the occurrence of many rare minerals. Outside of Sweden, its presence has also been reported in the Foote Lithium Co. mine in Kings Mountain, North Carolina, USA.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with sharp, well-formed, and transparent crystals of intense, yellowish-orange color are most valued by collectors. Rich groups of crystals or single, but clearly exposed crystals on a contrasting matrix (e.g., on white calcite) are also highly regarded. Due to their small size, the quality of the crystal itself is crucial, rather than the size of the entire sample. ## Popular Localities By far the most sought-after and classic specimens come from the Långban mine in Sweden. Material from this locality is considered exemplary for this species.

Care and storage

## Cleaning Tetrawikmanite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its rarity and small crystal size, mechanical cleaning is discouraged. If liquid is necessary, distilled water is recommended, but prolonged immersion should be avoided. ## What to Avoid Contact with acids and other aggressive chemicals that can damage the crystal surface should be avoided. The mineral is relatively soft, so it must be protected from scratching by harder minerals. It should not be heated or subjected to ultrasound. ## Storage Tetrawikmanite specimens, as microminerals, are best stored in specialized micromount boxes, which protect them from dust, mechanical damage, and direct contact. Exposure to moisture and extreme temperatures should be avoided.

Sources

IMA Mineral List (CNMNC)