Kraisslite
Chemical formula: Zn<sup>2+</sup><sub>3</sub>(Mn<sup>2+</sup>,Mg)<sub>25</sub>(Fe<sup>3+</sup>,Al)(As<sup>3+</sup>O<sub>3</sub>)<sub>2</sub>[(Si,As<sup>5+</sup>)O<sub>4</sub>]<sub>10</sub>(OH)<sub>16</sub>
Kraisslite is an extremely rare zinc and manganese arsenosilicate, forming small, hexagonal, reddish-brown crystals.
Properties
- Mohs hardness
- 4
- Luster
- Vitreous
- Streak
- Brown
- Density
- 4.01
- Cleavage
- Good on {0001}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Hexagonal
Diagnostic features
## Identification Field identification of kraisslite is practically impossible due to the size of the crystals. Identification requires specialized laboratory equipment, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). In a collection, it can be recognized by the characteristic form of radial aggregates of fine, reddish-brown needles on a rock matrix, originating from the type locality (Sterling Hill). ## Distinguishing from Similar Minerals It can be confused with other rare manganese minerals from Franklin and Sterling Hill, such as holdenite or retzian. Differentiation from these is only possible using advanced analytical methods. Kraisslite stands out with its unique chemical composition, being both an arsenate and a silicate. ## Crystal Forms Kraisslite forms slender, prismatic to acicular crystals with a hexagonal cross-section. It most often occurs in the form of radial or stellate aggregates and rosettes, as well as fibrous masses.
Geological environment
## Genesis Kraisslite is a mineral of metamorphic origin. It formed as a result of the metamorphism of the zinc, iron, and manganese ore deposit at Sterling Hill. It occurs in fissures and small cavities in skarns and franklinite-willemite ores. ## Mineral Associations This mineral co-occurs with other, often rare, minerals from the Franklin-Sterling Hill deposit. The most common associated minerals include: willemite, franklinite, calcite, andradite, rhodochrosite, barite, as well as rarer ones such as leucophoenicite, jerrygibbsite, holdenite, and torreyite. ## Localities The only confirmed occurrence of kraisslite in the world is its type locality: the Sterling Mine in Sterling Hill, Ogdensburg, Sussex County, New Jersey, USA.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of a kraisslite specimen is determined by the richness and development of crystals in aggregates. The most prized specimens are those with clearly visible, radial rosettes of reddish-brown crystals, contrasting with a light matrix (e.g., with calcite or willemite). Due to the microscopic nature of the mineral, the aesthetics of the entire aggregate, rather than a single crystal, are key. The presence of rare associated minerals is also important. ## Popular Localities The only source of kraisslite specimens is the historic Sterling Mine in New Jersey. All specimens available on the collector's market come from this single location and are part of old collections.
Care and storage
## Cleaning Kraisslite specimens, due to their fragility and microscopic size, generally should not be cleaned mechanically or chemically. If cleaning is absolutely necessary, compressed air (from a safe distance) can be used to remove loose dust. ## What to Avoid Avoid contact with water, acids, chemicals, and ultrasound. The crystals are very brittle and susceptible to mechanical damage. The specimen should be protected from vibrations and impacts. ## Storage It is recommended to store specimens in stable conditions, in closed "micromount" boxes, which protect against dust and mechanical damage. Avoid exposure to direct sunlight, although its light sensitivity is not known.