Chinchorroite
Chemical formula: Na₂Mg₅(As⁵⁺₂O₇)₂(As⁵⁺O₃OH)₂(H₂O)₁₀
Chinchorroite is a rare sodium magnesium arsenate, forming colorless, tabular crystals, discovered in the Torrecillas mine in Chile.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.75
- Cleavage
- {100} and {010}
- Fracture
- Sub-Conchoidal,Step-Like
- Transparency
- Transparent
- Crystal system
- Triclinic
Diagnostic features
## Identification Chinchorroite is difficult to identify visually without specialized equipment. It is recognized by its form of small, colorless, tabular crystals forming fan-shaped aggregates. Its low hardness (2.5) and occurrence in paragenesis with other rare arsenates at the type locality are key indicators. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other colorless, secondary arsenate or sulfate minerals, such as gypsum or pharmacolite. It is distinguished from them by its specific crystal form (thin tabular crystals in rosette aggregates) and unique occurrence environment. Unlike gypsum, it has a slightly higher hardness. ## Crystal Forms Crystals are thin, tabular, with a bladed habit. They typically occur as fan-shaped or rosette-like aggregates, forming delicate, radiating structures.
Geological environment
## Genesis Chinchorroite is a secondary mineral that forms in the oxidation zone (gossan) of polymetallic deposits under extremely arid (desert) climatic conditions. It formed as a result of weathering processes of primary arsenical ore minerals, in the presence of sodium and magnesium derived from surrounding rocks. ## Mineral Associations This mineral co-occurs with other rare arsenates at its type locality. It has been found in association with minerals such as magnesiofarmacoalumite, nickenichite, pharmacoalumite, anhydrite, quartz, hematite, and goethite. ## Localities The only confirmed occurrence of chinchorroite in the world is its type locality – the Torrecillas mine, located approximately 75 km east of the city of Iquique in the Tarapacá Region of northern Chile.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of chinchorroite specimens is primarily assessed based on the richness and aesthetics of the crystal aggregates. The most valued specimens are those with well-formed, distinct fan-shaped or rosette-like aggregates of colorless crystals, contrasting with the rock matrix. Due to the microscopic size of the crystals, their abundance on a given rock fragment is crucial. Purity and lack of damage to delicate aggregates also significantly increase their collector's value. ## Popular Localities The only source of chinchorroite specimens is the Torrecillas mine in Chile. All specimens available on the collector's market originate from this single location.
Care and storage
## Cleaning Chinchorroite specimens should be cleaned with the utmost care, exclusively using compressed air to remove dust. Due to its softness and potential solubility, contact with water and any chemical agents should be avoided. ## What to Avoid Contact with water, acids, detergents, and other liquids must be strictly avoided. The mineral is very soft and brittle, making it susceptible to mechanical damage. It should be protected from high temperatures and direct sunlight, which can lead to dehydration. ## Storage It is recommended to store specimens in closed, stable "micromount" containers, protecting them from dust, moisture, and physical damage. It is best kept in a dry place with a constant temperature.