Richellite

Chemical formula: CaFe<sup>3+</sup><sub>2</sub>(PO<sub>4</sub>)<sub>2</sub>(OH,F)<sub>2</sub>

Richellite is a rare, hydrated calcium and iron phosphate, forming characteristic, radial aggregates of an intensely yellow to brown color.

## Characteristics Richellite is a rare phosphate mineral, usually occurring as spherical or hemispherical aggregates with a radial-fibrous structure. Less commonly, it forms earthy or massive aggregates. Its structure is often delicate and brittle. Due to its appearance and rarity, it is primarily valued by collectors specializing in phosphate minerals. ## Physical Properties This mineral is characterized by a Mohs hardness of approximately 2, which makes it very soft. It has a luster described as dull, earthy, or silky in the case of fibrous aggregates. It is an opaque mineral or at most translucent on thin edges. Its density is approximately 3.33 g/cm³. ## Colors and Varieties Richellite occurs in shades from yellow, through yellowish-brown, orange-brown, to reddish-brown. No named varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality in 1883 – Richelle near Visé in Belgium. It was described by Belgian mineralogists, Max Lohest and A. Stassart.

Properties

Mohs hardness
2
Luster
Dull
Streak
Yellow-brown
Density
3.33
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Translucent to opaque
Crystal system
Triclinic

Diagnostic features

## Identification Richellite is most easily recognized by its characteristic mode of occurrence – spherical, radial aggregates. The intense, yellowish-brown color and low hardness (it can be scratched with a fingernail) are also key diagnostic features. ## Distinguishing from Similar Minerals It can be confused with other secondary phosphate minerals of similar color, such as cacoxenite or strengite, but differs from them in the form of aggregates. Cacoxenite forms acicular, fluffy crusts, while strengite more often occurs in botryoidal or reniform aggregates with a vitreous luster. Chemical tests confirming the presence of calcium and iron are the ultimate method of identification. ## Crystal Forms This mineral does not form well-developed, macroscopically visible crystals. It occurs in the form of radial-fibrous aggregates, spherical aggregates (spherulites), crusts, and earthy masses.

Geological environment

## Genesis Richellite is a secondary phosphate mineral. It forms in the oxidation zones of deposits containing phosphate minerals, as a result of weathering and alteration of primary phosphates in the presence of iron-rich solutions. It forms in voids and fractures of sedimentary rocks, mainly limestones and shales. ## Mineral Associations It co-occurs with minerals such as delvauxite, strengite, wavellite, apatite, koninckite, as well as with iron oxides (goethite, hematite) and calcite. ## Localities The most important locality, which is also the type locality, is Richelle in Belgium. This mineral has also been found in Březina and St. Benigna in the Czech Republic, and in the Silver Coin mine in Valmy, Nevada, USA.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, spherical aggregates of intense, vibrant color. Contrast with the rock matrix and the absence of damage to the delicate mineral structure are also important. Specimens from the historical locality in Belgium have particular value. ## Popular Localities Classic and most sought-after specimens come from the type locality in Richelle, Belgium. Specimens from the Czech Republic and the USA are also found in collections, though less frequently.

Care and storage

## Cleaning Richellite specimens are very delicate and brittle. They should only be cleaned with a soft, dry brush to remove dust. Any contact with water, and especially with chemicals, is highly inadvisable. ## What to Avoid Avoid washing with water, ultrasonic cleaning, and all types of chemicals. The mineral is soft and susceptible to mechanical damage, so it should be protected from scratches, impacts, and vibrations. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from dust and physical damage. Avoid exposure to moisture.

Sources

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