Polyarsite
Chemical formula: Na₇CaMgCu²⁺₂(As⁵⁺O₄)₄F₂Cl
Polyarsite is a very rare sodium, calcium, magnesium, and copper arsenate, discovered in fumaroles of the Tolbachik volcano in Russia.
Properties
- Mohs hardness
- 3
- Color
- sky-blue to light blue
- Luster
- Vitreous
- Streak
- white
- Density
- 3.592
- Cleavage
- None
- Fracture
- Irregular/Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Identification of polyarsite is possible only through advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS/WDS). Visually, it is practically indistinguishable from other rare copper arsenates from the same locality. ## Distinguishing from Similar Minerals It can be confused with other blue and green arsenates found in Tolbachik fumaroles, such as lammerite, eriostevensite, or popovite. Definitive differentiation requires specialized laboratory equipment. ## Crystal Forms Polyarsite forms very small, thin, tabular crystals with outlines ranging from hexagonal to irregular. They occur as single, dispersed crystals or form small, loose aggregates and coatings.
Geological environment
## Genesis Polyarsite is a mineral of volcanic origin, crystallizing from gases (sublimates) in high-temperature exhalative fumaroles. It forms at temperatures of about 500-600°C in an environment rich in arsenic, copper, sodium, and halogens. ## Mineral Associations It co-occurs with other rare fumarolic minerals, such as hematite, tenorite, aphthitalite, johillerite, eriostevensite, popovite, lammerite, urusovite, arsenatrotitanite, and svabite. ## Localities The only confirmed occurrence of polyarsite in the world is its type locality - the Arsenatnaya fumarole on the second cone of the Northern Breakthrough of the Great Fissure Eruption of Tolbachik volcano in Kamchatka, Russia.
Rarity
Extremely rare
For collectors
## Quality Criteria As a microscopic mineral, polyarsite is valued primarily for its mere presence in a collection. Specimens with well-formed, though still very small, crystals of intense blue or blue-green color, clearly contrasting with the host rock, are most highly rated. Association with other rare minerals from this locality is also important. ## Popular Localities All specimens available on the collector's market come from a single location in the world - the Tolbachik volcano in Kamchatka. They are obtained during rare and dangerous scientific expeditions.
Care and storage
## Cleaning Due to its extreme rarity and delicacy, polyarsite specimens should not be cleaned mechanically or chemically. Any contaminants are best left untouched. If absolutely necessary, compressed air can be used from a safe distance. ## What to Avoid Avoid contact with water, acids, cleaning agents, and ultrasound. The mineral is brittle and sensitive to changes in temperature and humidity. It should not be exposed to direct sunlight. ## Storage Polyarsite specimens, typically microscopic and on a rock matrix, should be stored exclusively in specialized, sealed "micromount" boxes, protecting them from dust, humidity, and mechanical damage.