Petersite-(Ce)

Chemical formula: Cu²⁺₆Ce³⁺(PO₄)₃(OH)₆·₃H₂O

Petersite-(Ce) is a rare, yellowish-green mineral from the mixite group, known for its fine, acicular crystals forming crusts and rosettes.

## Characteristics Petersite-(Ce) is a hydrated copper and cerium phosphate, belonging to the mixite group. It occurs as fine, acicular or hair-like crystals, which often form radial aggregates, rosettes, spherical clusters, or crusts on the host rock. Its typical appearance is delicate, silky or dull coatings with a characteristic yellowish-green color. ## Physical Properties This mineral is characterized by a hardness of 3.5 on the Mohs scale. It is translucent and has a white streak. Its density is approximately 3.42 g/cm³. Crystals exhibit a silky luster, while earthy aggregates are dull. ## Colors and Varieties Petersite-(Ce) occurs in a uniform, yellowish-green color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Joseph J. Peters (1940-2019), curator of the mineralogical collection at the American Museum of Natural History in New York, for his contributions to mineralogy. The "(Ce)" suffix in the name indicates the dominant rare earth element – cerium. The mineral was first described in 1982 by Pete J. Dunn, Donald R. Peacor, and William B. Simmons. ## Uses Due to its rarity and microscopic crystal size, petersite-(Ce) has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or minerals of the mixite group.

Properties

Mohs hardness: 3.5
Luster: Silky
Streak: white
Density: 3.424
Fracture: None observed
Transparency: Translucent
Crystal system: Hexagonal

Diagnostic features

## Identification Characteristic features of petersite-(Ce) include its yellowish-green color, occurrence in the form of fine, acicular crystals forming radial aggregates or crusts, and co-occurrence with other secondary copper minerals. ## Distinguishing from Similar Minerals Petersite-(Ce) can be confused with other minerals from the mixite group, such as agardite or mixite itself. Differentiation requires advanced chemical analyses (EDS/WDS) to determine the dominant rare earth element. Visually, it may also resemble other secondary green copper minerals, but its specific crystal habit is helpful in identification. ## Crystal Forms The mineral forms very fine, elongated, acicular or hair-like crystals, which combine into radial aggregates, rosettes, spherical clusters, and thin crusts and coatings.

Geological environment

## Genesis Petersite-(Ce) is a secondary mineral, forming in the oxidation (weathering) zones of copper ore deposits, in the presence of minerals containing phosphorus and rare earth elements. ## Mineral Associations It most commonly co-occurs with other secondary minerals, such as chrysocolla, malachite, and also with quartz, which constitutes the host rock. ## Localities The most important and also the type locality (localitas typica) is the Cherry Creek mining district in Yavapai County, Arizona, USA. This is the only confirmed and well-documented locality for this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria For collectors, the most valuable specimens are those with clearly formed, radial aggregates of acicular crystals, forming aesthetic crusts on a contrasting substrate, most often on quartz. The intensity and uniformity of the yellowish-green color also enhance the specimen's attractiveness. The absence of damage to the delicate crystal structures is important. ## Popular Localities The only source of petersite-(Ce) specimens is its type locality in Arizona, USA. All samples available on the collector's market originate from this single location.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Contact with water and any chemical agents should be avoided, as they can damage the delicate crystals. ## What to Avoid Ultrasonic cleaners, high temperatures, humidity, and all acids and bases should be avoided. Prolonged exposure to intense sunlight may not be advisable, although there is no specific data on its effects. ## Storage It is recommended to store specimens in a dry place, in closed boxes or display cases, to protect them from dust and mechanical damage. Due to its fragility, avoid placing other minerals directly on its surface.

External references

https://www.mindat.org/min-46097.html