Metasideronatrite
Chemical formula: Na₂Fe³⁺(S⁶⁺O₄)₂(OH)·H₂O
Metasideronatrite is a rare, secondary sodium iron sulfate, forming tiny, yellow crystals and efflorescences in dry, desert conditions.
Properties
- Mohs hardness
- 1.5-2.5
- Color
- Golden yellow, straw yellow; yellow in transmitted light.
- Luster
- Vitreous, Pearly
- Streak
- Light yellow
- Density
- 2.68
- Cleavage
- Perfect on {100} {010}. Nearly perfect on {001}.
- Fracture
- Fibrous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Metasideronatrite is identified by its characteristic yellow color, occurrence as fine crystals, efflorescences, and crusts in dry oxidation zones. A key diagnostic feature is its instability in contact with water – it readily rehydrates, changing its appearance. It is very soft and brittle. ## Distinguishing from Similar Minerals It can be confused with other secondary iron sulfates, such as jarosite, copiapite, or sideronatrite. It differs from sideronatrite in crystal habit (sideronatrite forms acicular or fibrous crystals) and a lower degree of hydration, which is a feature difficult to verify without laboratory analysis. It is distinguished from jarosite and copiapite by its often lighter, lemon-yellow hue and specific mineral parageneses. ## Crystal Forms Crystals are usually very small, with a tabular or bladed habit, often arranged in rosette-like aggregates. It also occurs as granular, powdery, and brittle encrustations.
Geological environment
## Genesis Metasideronatrite is a secondary mineral, typical of oxidation zones of ore deposits in arid and desert climates. It forms from the weathering of iron sulfides, mainly pyrite, in the presence of sodium-rich solutions. It is a product of dehydration of sideronatrite under very dry atmospheric conditions. ## Mineral Associations It often co-occurs with other sulfates, such as sideronatrite, copiapite, jarosite, metavoltine, as well as gypsum, halite, and hematite. ## Localities The most important and classic localities for metasideronatrite are in the Atacama Desert in Chile, particularly in the Antofagasta regions (e.g., Sierra Gorda, Chuquicamata) and Atacama (San Simon mine). It is also known from a volcanic island in the Aegean Sea in Greece; from mines in Utah and Nevada (USA); from Pécs in Hungary; and from a dried lake in Tibet (China).
Rarity
Rare
For collectors
## Quality Criteria The most prized metasideronatrite specimens are those with well-formed, albeit microscopic, crystals forming rich efflorescences or druses on a rock matrix. An intense, lemon-yellow color is desirable. Due to the fragility and instability of the mineral, undamaged, well-preserved specimens from known localities (especially from Chile) command higher value. ## Popular Localities Classic and most sought-after specimens by collectors come from the Atacama Desert in Chile, which is the type locality for this mineral.
Care and storage
## Cleaning Metasideronatrite specimens are extremely sensitive to water and moisture. They must absolutely not be wet cleaned. To remove dust, a very soft, dry brush or compressed air from a distance and with low force can be used to avoid damaging the fragile crystals. ## What to Avoid Avoid contact with water, water vapor, and any liquids, which will cause it to dissolve or transform into sideronatrite. It should be protected from high air humidity. This is a very soft mineral, so all physical contact and vibrations should be avoided. ## Storage Storage requires sealed, airtight containers (so-called perky boxes) with the addition of a moisture-absorbing agent, such as silica gel. It should be stored at a stable room temperature, away from heat sources and direct sunlight.