Dollaseite-(Ce)

Chemical formula: CaCe³⁺Mg₂Al(Si₂O₇)(SiO₄)(OH)F

Dollaseite-(Ce) is a rare mineral from the epidote group, characterized by its brown color and occurrence in radial aggregates.

## Characteristics Dollaseite-(Ce) is a mineral belonging to the epidote group. It forms elongated, acicular crystals that often coalesce into radial or fan-shaped aggregates. Individual crystals rarely exceed 1 mm in length. It is most commonly observed as small clusters within the host rock. ## Physical Properties This mineral is characterized by a hardness of approximately 6.5-7 on the Mohs scale. It has a vitreous to resinous luster. It is translucent to nearly opaque. Its density is approximately 3.97 g/cm³. ## Colors and Varieties Dollaseite-(Ce) occurs in shades of brown, from reddish-brown to dark brown. No distinct color varieties or commercial varieties are recognized. ## History and Name The mineral's name comes from Wayne A. Dollase (1938–), an American mineralogist from the University of California, who made significant contributions to the study of the crystal structure of minerals from the epidote group. The "-(Ce)" suffix refers to the dominant rare earth element – cerium. The mineral was first described in 1987 based on samples from the Östanmossa mine in Sweden.

Properties

Mohs hardness: 6.5-7
Color: Brown
Luster: Vitreous to Resinous
Streak: Brown
Density: 3.90
Cleavage: Good on {001}
Fracture: Uneven
Transparency: Translucent to nearly Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features of dollaseite-(Ce) include its brown color, radial aggregates composed of small, acicular crystals, and high hardness. It occurs in a specific geological environment, which aids identification. ## Differentiation from Similar Minerals It can be confused with other brown epidote-group minerals, such as allanite-(Ce). Definitive differentiation often requires advanced analytical methods, such as EDS spectroscopy, to confirm the chemical composition, especially the content of magnesium and fluorine. ## Crystal Forms It forms prismatic, acicular crystals, elongated along the crystallographic b-axis. These crystals almost always occur as radial, fan-shaped, or spherulitic aggregates.

Geological environment

## Genesis Dollaseite-(Ce) is a hydrothermal or metamorphic mineral. It forms as a result of metasomatism in skarns or altered carbonate rocks. Its presence is associated with processes of rare earth element enrichment. ## Mineral Associations It often co-occurs with minerals such as tremolite, calcite, fluorite, titanite, apatite, talc, and other epidote-group minerals, e.g., allanite-(Ce). ## Localities The most important and classic locality, from which the type material originates, is the Östanmossa iron ore mine in the Norberg region of Sweden. It is also known from several other localities worldwide, including Romania (Oravița) and Italy (Baveno).

Rarity

Very rare

For collectors

## Quality Criteria The most sought-after specimens by collectors are those with well-formed, distinct radial aggregates of intense, brown color, contrasting with a light host rock (matrix). The size of the aggregates and the absence of mechanical damage significantly increase the specimen's value. ## Popular Localities Specimens from the type locality, the Östanmossa mine in Sweden, are most prized due to their historical significance.

Care and storage

## Cleaning Due to the acicular structure of the aggregates, mechanical cleaning is risky. Only gentle rinsing in distilled water is recommended to remove loose contaminants. Ultrasonic cleaners should be avoided, as they can damage delicate crystals. ## What to Avoid Avoid contact with acids and strong chemical agents. Brittle aggregates are sensitive to impacts and shocks. ## Storage Dollaseite-(Ce) specimens should be stored under stable conditions, away from dust and shocks. It is best to place them in a closed display box to protect the delicate needles from damage.