Rosièresite

Chemical formula: PbxCuyAlz(PO₄)m·nH₂O

Rosièresite is a rare, hydrated mixture of aluminum, copper, and lead phosphates, forming reniform or spherical aggregates with colors ranging from green to bluish-green.

## Characteristics Rosièresite is a mineraloid, meaning it is a substance with a disordered internal structure, rather than a fully crystallized mineral. It occurs as spherical, reniform, or botryoidal aggregates, often with a concentric internal structure. Its surface can be smooth or dull. It is typically found as thin crusts on other minerals or rocks. ## Physical Properties Due to its amorphous nature, rosièresite does not exhibit typical mineral crystals or cleavage. Its Mohs hardness is variable, ranging from 3 to 4. The luster is most often vitreous to dull. It is an opaque mineral. ## Colors and Varieties It is characterized by colors ranging from green, through bluish-green, to turquoise. The color is usually uniform, although concentric zones with varying color saturation may be visible in cross-sections of aggregates. No named varieties are distinguished. ## History and Name The mineral's name comes from the location of its first description – the Rosières mine near Carmaux in France. It was first described by the French chemist and mineralogist Félix Pisani in 1864. For many years, rosièresite's status as a distinct mineral species was questioned; it is currently classified as a mineral mixture or mineraloid, and not an IMA-approved mineral. ## Uses Due to its rarity and small aggregate sizes, rosièresite has no industrial application. It is solely an object of interest for collectors of rare minerals.

Properties

Mohs hardness: 3-4
Luster: Vitreous to Dull
Streak: Greenish white
Cleavage: None
Fracture: Conchoidal
Transparency: Opaque

Diagnostic features

## Identification Characteristic features of rosièresite include its specific forms of occurrence – spherical, reniform, or botryoidal aggregates – and its intense, bluish-green color. It is relatively soft and opaque. It often forms thin coatings on other minerals. ## Distinguishing from Similar Minerals It can be confused with other secondary copper minerals of similar color and form, such as turquoise, chrysocolla, or variscite. It is usually softer than turquoise. Distinguishing it from chrysocolla, which is also amorphous, can be difficult and often requires chemical analysis to confirm the presence of aluminum and phosphorus. Variscite rarely contains copper and lead, which is key in compositional analysis. ## Crystal Forms As an amorphous substance (mineraloid), rosièresite does not form crystals. It occurs exclusively in the form of massive, spherical (spherulitic), reniform, and botryoidal aggregates, as well as crusts.

Geological environment

## Genesis Rosièresite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits, mainly copper and lead. It forms as a result of phosphate-rich waters acting on minerals containing aluminum, copper, and lead. Its formation is associated with acidic environments. ## Mineral Associations It most commonly co-occurs with minerals typical of oxidation zones, such as chalcopyrite, galena, sphalerite (as primary minerals), as well as anglesite, cerussite, pyromorphite, mimetite, and also with clay minerals and iron oxides (e.g., goethite). ## Localities The most important and historical locality, from which the name originates, is the Rosières mine near Carmaux in the Tarn department, France. Other known localities include the Silver Hill mine in North Carolina (USA) and some old mining dumps in Cornwall (United Kingdom).

Rarity

Very rare

For collectors

## Quality Criteria The most valued by collectors are specimens with well-formed, spherical or reniform aggregates of intense, bluish-green color. The contrast with the rock matrix on which the rosièresite occurs is also important. Specimens from the historical type locality (Rosières, France) are particularly sought after due to their scientific significance and rarity.

Care and storage

## Cleaning Rosièresite specimens should be cleaned very carefully, preferably using a soft brush to remove dust. Compressed air can be used from a safe distance. Due to its porous nature and possible reactivity, contact with water, especially detergents, should be avoided. ## What to Avoid All chemicals, acids, and solvents should be strictly avoided. The mineral is sensitive to high temperatures and prolonged exposure to direct sunlight, which can cause fading or structural changes. It is brittle and sensitive to impact. ## Storage It is recommended to store specimens in closed, stable containers (e.g., "membrane box" type boxes) or display cases, away from heat sources, moisture, and direct light. It should be protected from dust and mechanical damage.

Sources

IMA Mineral List (CNMNC)