Wermlandite
Chemical formula: Mg₇Al₂(OH)₁₈[Ca(H₂O)₆](S⁶⁺O₄)₂·6H₂O
Wermlandite is a rare, hydrated magnesium and aluminum sulfate, forming small, hexagonal crystals with a pearly luster, found in manganese skarns.
Properties
- Mohs hardness
- 1.5
- Color
- Green-gray
- Luster
- Pearly, Vitreous
- Streak
- White to light gray green
- Density
- 1.932
- Cleavage
- Perfect on {0001}
- Fracture
- Micaceous
- Transparency
- Translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification The characteristic features of wermlandite are its small, hexagonal, tabular crystals, often grouped into rosette-like aggregates. Pearly luster on basal surfaces, very low hardness, and occurrence in a specific geological environment (manganese skarns) are key for its identification. It dissolves in hydrochloric acid. ## Distinguishing from Similar Minerals Wermlandite can be confused with other minerals from the hydrotalcite group, such as motukoreite or nikischerite, which form similar aggregates. Final differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). Visually, it may resemble small gypsum crystals or some micas, but it differs from them in crystal habit and paragenesis. ## Crystal Forms Crystals are thin, tabular, with a hexagonal outline. They usually occur as single, dispersed plates on the rock matrix or form small, rosette-like and spherulitic aggregates.
Geological environment
## Genesis Wermlandite is a secondary mineral, formed as a result of hydrothermal processes within manganese and iron ore deposits that have undergone contact metamorphism, creating skarns. It forms in fissures and small rock cavities. ## Mineral Associations This mineral co-occurs with other rare minerals typical of the Långban deposit. It is most commonly associated with calcite, barite, hausmannite, fluorapatite, phlogopite, and other minerals from the hydrotalcite group. ## Localities The most important and classic occurrence of wermlandite is its type locality - the Långban mine in Värmland, Sweden. This is a site known for the occurrence of many rare and unique minerals. Outside Sweden, its presence has also been reported in the Khibiny intrusive complex on the Kola Peninsula in Russia.
Rarity
Very rare
For collectors
## Quality Criteria For wermlandite collectors, the quality and form of the crystals are most important, despite their microscopic size. Specimens with well-formed, sharp, hexagonal crystals forming aesthetic, rosette-like aggregates are most valued. The matrix is also important - a color-contrasting rock substrate (e.g., dark hausmannite) enhances the attractiveness of the specimen. The clarity and transparency of the crystals also affect the value. ## Popular Localities By far the most sought-after and historically significant specimens come from the type locality - the Långban mine in Sweden. This is practically the only source of collectible material available on the market.
Care and storage
## Cleaning Wermlandite specimens should be handled with extreme caution due to their extreme delicacy. Mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used from a safe distance to remove dust. Avoid contact with water, which can damage or dissolve the mineral. ## What to Avoid Contact with water, acids, and other chemicals should be strictly avoided. The mineral is very soft and susceptible to scratches. It should not be heated or exposed to prolonged sunlight, although its fading has not been documented. ## Storage It is recommended to store wermlandite specimens exclusively in specialized micromineral boxes (micromounts), which protect them from dust, mechanical damage, and changes in humidity. Display should only be done under a microscope.