Plumbojarosite

Chemical formula: Pb²⁺₀.₅Fe³⁺₃(S⁶⁺O₄)₂(OH)₆

Plumbojarosite is a rare lead and iron sulfate from the alunite group, forming small, tabular crystals of a characteristic golden-brown color.

## Characteristics Plumbojarosite is a hydrated lead and iron sulfate belonging to the alunite group. It most commonly occurs as earthy aggregates, crusts, or microcrystalline masses. Well-formed crystals are rare and usually very small, taking on a tabular or rhombohedral habit. The mineral is opaque, less commonly translucent, with a characteristic golden-brown to dark brown, or even black color. ## Physical Properties Plumbojarosite is a very soft mineral, with a hardness of only 1.5-2 on the Mohs scale, meaning it can be scratched with a fingernail. Its density is approximately 3.67 g/cm³, making it noticeably heavier than most common minerals. The luster is dull or earthy in the case of massive aggregates, and on crystal faces, it can be vitreous to resinous. ## Colors and Varieties This mineral occurs in shades from golden-brown, through dark brown and reddish-brown, to almost black. No named color varieties or commercial varieties are distinguished. ## History and Name The name plumbojarosite refers to its chemical composition – the presence of lead (Latin: *plumbum*) – and its structural similarity to jarosite. The mineral was first described in 1902 based on samples from the Cookes Peak Mining District in Luna County (New Mexico, USA), which is its type locality. ## Uses Plumbojarosite has no industrial significance. However, it is an interesting mineral for advanced collectors specializing in rare minerals, especially those from the sulfate group, and for locality collectors.

Properties

Mohs hardness
1.5-2
Luster
Vitreous, Resinous, Dull, Earthy
Streak
Pale yellow
Density
3.665
Cleavage
Fair on {10_14}.
Fracture
Micaceous
Transparency
Translucent,Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Plumbojarosite most often forms earthy or powdery coatings and crusts with a characteristic golden-brown or yellowish-brown color. A key diagnostic feature is its very low hardness (1.5-2 on the Mohs scale) and a pale yellow streak. Its occurrence in the oxidation zones of lead ore deposits is also an important clue. ## Distinguishing from Similar Minerals It can be confused with other minerals from the alunite group, such as jarosite or natrojarosite. Distinguishing them without advanced chemical analysis (checking for the presence of lead) is practically impossible. Goethite can also have a similar appearance, but it is much harder (5-5.5) and has a yellowish-brown streak. ## Crystal Forms Well-formed crystals are rare and usually microscopic in size. They take the form of small, hexagonal tablets or rhombohedra. It is most commonly found as earthy aggregates, powdery coatings, crusts, and compact masses.

Geological environment

## Genesis Plumbojarosite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits, especially in the presence of lead minerals (such as galena) and iron minerals (such as pyrite). It forms under strongly acidic and oxidizing conditions, often in arid or semi-arid climates. ## Mineral Associations It often co-occurs with minerals typical of oxidation zones, such as anglesite, cerussite, galena, pyrite, sphalerite, goethite, hematite, as well as other sulfates from the alunite group, e.g., jarosite and beaverite. ## Localities Important localities worldwide include the type locality in New Mexico (USA), as well as other places in the USA (e.g., Arizona, Nevada). It is also known from Greece (Laurion mines), Spain (Sierra Almagrera), Italy (Sardinia), Namibia (Tsumeb), and Australia.

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, visible-to-the-naked-eye crystals, which is a great rarity for this mineral. An intense, golden-brown color and a contrasting association with other minerals, e.g., with blue anglesite, also enhance its attractiveness. However, the vast majority of available specimens are microcrystalline crusts and coatings. ## Popular Localities Specimens with visible crystals mainly come from historical localities, such as the mines in Laurion, Greece, or some mines in Arizona (USA). Material from the type locality in New Mexico is primarily of historical significance.

Care and storage

## Cleaning Plumbojarosite specimens are extremely delicate and soft. They should be cleaned only very carefully, using a soft brush to remove dust. Due to its fragility and low hardness, wet cleaning is not recommended, especially the use of ultrasonic cleaners. ## What to Avoid This mineral is sensitive to chemicals, including acids and strong bases. Contact with any cleaning agents should be avoided. Due to its micaceous cleavage and low hardness, it is very susceptible to mechanical damage, such as scratches or chipping. ## Storage Plumbojarosite should be stored separately, in a closed display box, away from harder minerals that could scratch it. It is not sensitive to light, but it should be protected from dust and physical damage.

External references

Sources

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