Redingtonite
Chemical formula: Fe<sup>2+</sup>Cr<sup>3+</sup><sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>4</sub>·22H<sub>2</sub>O
Redingtonite is a very rare, hydrated iron and chromium sulfate, forming fine, purple coatings and efflorescences.
Properties
- Mohs hardness
- 1-2
- Luster
- Silky
- Streak
- Light purple
- Density
- 1.76
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Redingtonite can be identified by its characteristic purple color, fibrous or hair-like habit, and specific geological environment (oxidized sulfide deposits). Its extreme rarity and small size make field identification practically impossible. Confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis. ## Distinguishing from similar minerals Redingtonite can be confused with other secondary sulfates of purple color, such as cobaltite or some varieties of alums. Differentiation is based on chemical analysis, which will show the presence of chromium and iron, and on crystallographic studies. Unlike many other sulfates, redingtonite is associated with ultramafic rocks (serpentinites). ## Crystal forms This mineral forms very fine, acicular or hair-like crystals, which often arrange themselves into tangled aggregates and clusters. It also occurs as powdery or earthy coatings and efflorescences.
Geological environment
## Genesis Redingtonite is a secondary mineral, formed in the oxidation (weathering) zone of sulfide deposits, mainly pyrite, within ultramafic rocks such as serpentinites. It forms as a result of the reaction of acidic mine waters, rich in sulfates, with chromium-bearing minerals. ## Mineral associations This mineral co-occurs with other sulfates formed under similar conditions, such as knoxvilleite, alunogen, gypsum, epsomite, as well as with pyrite and chromite. ## Localities Redingtonite is an extremely rare mineral. Apart from the historical type locality – the Redington mine in California (USA) – its occurrence has been confirmed in only a few places worldwide, including the Bushveld Complex in South Africa and the Urals in Russia.
Rarity
Very rare
For collectors
## Quality criteria The quality of redingtonite specimens is assessed primarily based on the richness and intensity of the color of the coating or fibrous aggregates. Due to the microscopic nature of the crystals, their form is not the main criterion. The most valued specimens are those where redingtonite forms a clearly visible, intensely purple layer on a contrasting substrate (rock matrix). Association with other rare sulfates is also important. ## Popular localities The most classic and historical specimens come from the Redington mine in California, USA. However, they are practically unavailable on the collector's market. Currently, small amounts of material may come from other confirmed localities, but these are extremely rare.
Care and storage
## Cleaning Redingtonite specimens are extremely delicate and sensitive to water. They should not be cleaned mechanically or chemically. Any attempts at cleaning, especially with water, can lead to the dissolution and destruction of the mineral. It is best to leave it in its untouched state. ## What to avoid Contact with water and other liquids that can dissolve it must be strictly avoided. The mineral is sensitive to changes in air humidity – in dry air, it can dehydrate and disintegrate. It should be protected from high temperatures, direct sunlight, and all chemicals. ## Storage Redingtonite specimens require storage under specialized conditions. The safest way is to place them in a sealed, closed container (e.g., a "micromount" type), which protects against mechanical damage and stabilizes humidity. The container should be stored in a dark, cool place with constant humidity.