Hydroniumjarosite
Chemical formula: (H₃O)Fe³⁺₃(S⁶⁺O₄)₂(OH)₆
Hydroniumjarosite is a hydrated iron sulfate from the alunite group, forming microscopic, yellowish-brown crystals, often as earthy coatings.
Properties
- Mohs hardness
- 4-4.5
- Color
- Amber-yellow to dark brown.
- Luster
- Sub-adamantine to vitreous, resinous on fracture surfaces.
- Streak
- Pale yellow
- Density
- 2.9
- Cleavage
- Distinct on {0001}
- Fracture
- Irregular/Uneven,Sub-Conchoidal
- Transparency
- Translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification Macroscopic identification of hydroniumjarosite is impossible. Identification requires advanced analytical methods, such as X-ray diffraction (XRD) or infrared spectroscopy (IR). In the field, it may be suspected in oxidation zones of sulfide deposits, where it forms yellow or brown, earthy coatings. ## Differentiation from Similar Minerals It can be confused with other minerals from the jarosite group (jarosite, natrojarosite), as well as other secondary iron sulfates, such as goethite or limonite. Differentiation from these is only possible through chemical and structural analysis. ## Crystal Forms It forms microscopic, platy or rhombohedral crystals, which usually occur as earthy, powdery, or compact masses and crusts.
Geological environment
## Genesis Hydroniumjarosite is a secondary mineral, forming in acidic, sulfate-rich environments. It forms in oxidation (weathering) zones of ore deposits, especially pyrite and other iron sulfides. It also forms as a result of hydrothermal processes and in volcanic lake sediments. ## Mineral Associations It co-occurs with other minerals from the oxidation zone, such as jarosite, natrojarosite, goethite, hematite, pyrite, alunite, and quartz. ## Localities Confirmed occurrences of hydroniumjarosite are found in many places around the world. Key localities include, among others, the Apex mine in St. George, Utah (USA); the Iron Monarch quarry in South Australia; Vulcano Island in Italy; the Chuquicamata mine in Chile; as well as in Germany (Ronneburg mining areas) and Spain (Rio Tinto).
Rarity
Not very common
For collectors
## Quality Criteria Hydroniumjarosite is not a mineral valued by typical collectors due to its unattractive, earthy appearance and microscopic crystals. Its value is primarily scientific. For specialized collections (so-called "micromounts"), specimens with well-formed, though still microscopic, crystals from precisely defined localities are sought after.
Care and storage
## Cleaning Hydroniumjarosite specimens are very fragile and sensitive. Mechanical cleaning is not recommended. If necessary, compressed air can be used to remove dust. Contact with water should be avoided, as it can cause aggregates to disintegrate. ## What to Avoid Contact with water and all chemicals must be strictly avoided. The mineral is unstable in humid environments. It should not be heated or exposed to temperature changes. ## Storage Specimens should be stored in dry conditions, preferably in tightly sealed containers or display cases, away from sources of moisture. Due to its fragility, it should be kept away from places subject to shocks and vibrations.