Beaverite-(Cu)

Chemical formula: Pb<sup>2+</sup>Cu<sup>2+</sup>Fe<sup>3+</sup><sub>2</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>(OH)<sub>6</sub>

Beaverite-(Cu) is a rare secondary mineral from the alunite group, forming microscopic, yellow or greenish crystals and coatings in the oxidation zones of ore deposits.

## Characteristics Beaverite-(Cu) is a hydrated sulfate of lead, copper, and iron, belonging to the alunite supergroup. It most commonly occurs as earthy, powdery, or fibrous aggregates, as well as coatings and crusts on other minerals. Well-formed crystals are rare and appear as small, tabular or rhombohedral forms with a hexagonal outline, typically reaching sizes less than 1 mm. ## Physical Properties Crystals, though microscopic, exhibit a vitreous luster, or dull in the case of earthy aggregates. The mineral is brittle. Its Mohs hardness ranges from 3.5 to 4.5, and its density varies between 4.23 and 4.31 g/cm³. ## Colors and Varieties Beaverite-(Cu) ranges in color from canary yellow, through yellowish-green, greenish-brown, to brown. Its color is directly related to the copper-to-zinc ratio in its structure. No commercial or gemological varieties are distinguished. ## History and Name The mineral was first described in 1911 by B.S. Butler and W.T. Schaller based on samples from the Horn Silver Mine in Beaver County, Utah, USA. Its name comes from the type locality. The suffix "-(Cu)" was added in 2007 by the IMA to distinguish it from the newly defined, zinc analogue – beaverite-(Zn). ## Applications Beaverite-(Cu) has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals or mineral systematics, as well as scientists studying the oxidation zones of deposits.

Properties

Mohs hardness
3.5-4.5
Luster
Vitreous to dull
Streak
Light yellow
Density
4.23-4.31
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Beaverite-(Cu) is identified by its characteristic canary yellow to greenish color, its occurrence as earthy coatings or small, hexagonal crystals in the oxidation zones of polymetallic deposits. Its co-occurrence with other sulfates and minerals of lead, copper, and zinc is key. ## Distinguishing from Similar Minerals It can be confused with other secondary sulfates and arsenates of similar color, such as jarosite, plumbojarosite, beaverite-(Zn), or mimetite. It is distinguished from jarosite and plumbojarosite by the presence of copper, which contributes to more greenish hues. Final differentiation from beaverite-(Zn) and other very similar minerals from the alunite group requires advanced chemical analysis (e.g., EDS). ## Crystal Forms Most often, it forms microscopic, hexagonal crystals with a tabular or rhombohedral habit. It occurs mainly as very fine-grained, powdery, earthy, or fibrous aggregates, as well as thin coatings and crusts.

Geological environment

## Genesis It is a secondary mineral, forming in the oxidation zones (so-called gossans) of hydrothermal polymetallic ore deposits rich in lead, copper, and iron. It forms under low pH conditions as a result of the weathering of sulfides, mainly galena, chalcopyrite, and pyrite. ## Mineral Associations It often co-occurs with minerals such as anglesite, cerussite, galena, pyrite, sphalerite, quartz, jarosite, plumbojarosite, hematite, goethite, as well as other rare sulfates and arsenates of the oxidation zone. ## Localities Key localities worldwide include the type locality at the Horn Silver Mine (Utah, USA), as well as the Tiger Mine (Arizona, USA), Tsumeb (Namibia), Broken Hill (New South Wales, Australia), and deposits in the Rhodope Mountains (Bulgaria) and Laurion (Greece). In Poland, its occurrence has been noted in small quantities in zinc and lead ore mines in the Olkusz region.

Rarity

Rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp microcrystals of intense, canary yellow color. Rich crusts contrasting with the host rock (e.g., with quartz or galena) are also highly valued. Due to the microscopic nature of the crystals, their quality and photogenicity under magnification are crucial. ## Popular Localities Historical finds from the Tiger Mine in Arizona (USA) and Tsumeb in Namibia are considered classic and provide the best specimens. Specimens from these localities, characterized by exceptionally well-formed crystals, fetch the highest prices on the collector's market.

Care and storage

## Cleaning Specimens should only be cleaned very carefully, using a soft brush to remove dust. Due to its brittleness and often powdery form, wet cleaning is not recommended. If absolutely necessary, a minimal amount of distilled water can be used, and the specimen should be immediately dried with compressed air. ## What to Avoid Avoid contact with all chemicals, especially acids, which can damage it. The mineral is sensitive to shocks and ultrasound. It should not be heated or exposed to prolonged moisture. ## Storage Beaverite-(Cu) specimens, especially microscopic ones, are best stored in sealed, padded "micromount" boxes to protect them from dust and mechanical damage. Avoid storage in humid conditions.

Sources

Read more