Wenkite
Chemical formula: Ba<sub>4</sub>Ca<sub>6</sub>(Si,Al)<sub>20</sub>O<sub>41</sub>(OH)<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>3</sub>·H<sub>2</sub>O
Wenkite is a very rare, complex beryllium and calcium tectosilicate, forming fibrous aggregates with a silky luster.
Properties
- Mohs hardness
- 6
- Luster
- Silky
- Streak
- White
- Density
- 3.16
- Cleavage
- Imperfect on {1010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification A characteristic feature of wenkite is its radially fibrous aggregates with a silky luster, occurring in a specific geological environment – marbles. Due to its extreme rarity, field identification is practically impossible and requires advanced laboratory methods, such as X-ray diffraction (XRD) and chemical analysis. ## Distinguishing from similar minerals Wenkite's fibrous aggregates may resemble other zeolitic minerals or silicates of similar form, such as natrolite or scolecite. Differentiation is possible almost exclusively based on chemical and crystallographic analysis and knowledge of paragenesis (co-occurrence with other minerals). ## Crystal forms It forms elongated, prismatic crystals with a hexagonal cross-section, which almost always occur as radial or fibrous aggregates.
Geological environment
## Genesis Wenkite forms under conditions of high-grade contact metamorphism, within marbles (metamorphosed limestones). Its crystallization is associated with the presence of sulfates in calc-silicate skarns. ## Mineral associations This mineral co-occurs with calcite, diopside, titanite, phlogopite, pyrite, pyrrhotite, graphite, grossular, clinozoisite, and scolecite. ## Localities The most important and type locality is the marble quarry in Candoglia, in the Ossola Valley (Piedmont, Italy). It is also known from several other locations worldwide, including the Afrikanda intrusive complex on the Kola Peninsula in Russia and the Jacupiranga mine in São Paulo, Brazil.
Rarity
Very rare
For collectors
## Quality criteria For collectors, the size and quality of the formation of radial aggregates are most important. Specimens where the fibrous "suns" of wenkite are clearly visible against a contrasting background of the matrix rock (marble) are most valued. Due to its rarity, any well-formed and confirmed specimen is valuable. ## Popular localities By far the most valued and classic specimens come from the type locality in Candoglia, Italy. Material from other localities is extremely rare on the collector's market.
Care and storage
## Cleaning Due to the fibrous and delicate nature of the aggregates, mechanical cleaning is not recommended. Only careful use of compressed air to remove dust is permissible. Avoid contact with water and any chemicals. ## What to avoid Avoid ultrasonics, steam cleaners, acids, and detergents. The aggregates are brittle and sensitive to shocks and mechanical pressure. Store away from moisture. ## Storage Wenkite specimens are best stored in closed, padded collector boxes to protect them from dust, mechanical damage, and humidity changes.