Juansilvaite
Chemical formula: Na<sub>5</sub>Al<sub>3</sub>[As<sup>5+</sup>O<sub>3</sub>(OH)]<sub>4</sub>[As<sup>5+</sup>O<sub>2</sub>(OH)<sub>2</sub>]<sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·4H<sub>2</sub>O
Juansilvaite is an extremely rare, hydrated sodium aluminum arsenate and sulfate, forming colorless, tabular crystals in rosette-like aggregates.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- White
- Density
- 3.23
- Cleavage
- Perfect on {010}
- Transparency
- Transparent
- Crystal system
- Triclinic
Diagnostic features
## Identification Characteristic features of juansilvaite include its unique form – aggregates of thin, colorless, tabular crystals forming rosettes – and its extreme rarity, occurring in only one location worldwide. It is very soft and has a vitreous luster. Its association with halite and other rare arsenates from the Torrecillas mine is a key indicator. ## Distinguishing from Similar Minerals It can be confused with other colorless, soft secondary minerals, such as gypsum or other sulfates and arsenates. However, its characteristic rosette habit and unique occurrence environment usually allow for preliminary identification. Definitive differentiation from other rare arsenates from the same locality requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms thin, tabular to platy crystals, which are often curved. These crystals aggregate into radial or rosette-like clusters.
Geological environment
## Genesis Juansilvaite is a secondary mineral, formed under unique desert conditions. It forms as a result of weathering processes and alteration of primary arsenic-bearing minerals in a highly saline environment (evaporite deposits). Its formation is linked to volcanic activity and subsequent alteration of rocks in an arid climate. ## Mineral Associations It most commonly co-occurs with halite and magnesioaubertite. Other rare sulfates and arsenates characteristic of this locality can also be found in its vicinity. ## Localities The only confirmed occurrence of juansilvaite worldwide is its type locality – the Torrecillas mine, located in the Salar Grande area, in the Iquique province (Tarapacá region) in Chile.
Rarity
Extremely rare
For collectors
## Quality Criteria As an extremely rare mineral, every specimen is valuable to collectors specializing in systematics or rare minerals. Specimens with well-formed, undamaged crystal rosettes, good transparency, and luster are most highly prized. The attractiveness is enhanced by the placement of crystals on a contrasting matrix, for example, on halite. ## Popular Localities All known juansilvaite specimens come from a single location worldwide: the Torrecillas mine in Chile. This is the only source of this mineral.
Care and storage
## Cleaning Juansilvaite specimens are extremely delicate and sensitive to water. Only a soft, dry brush or carefully applied compressed air from a safe distance should be used for cleaning to remove dust. Absolutely avoid contact with water and other liquids. ## What to Avoid Contact with water and moisture, which can dissolve or damage the mineral, must be strictly avoided. It is very soft and susceptible to mechanical damage. As an arsenate, its dust is toxic if inhaled or ingested, so caution should be exercised when handling it. It should also be protected from high temperatures. ## Storage It is recommended to store specimens in a sealed, airtight container (e.g., a "membrane box") to protect them from moisture, dust, and physical damage. It is best to keep it in stable temperature conditions, away from direct sunlight.