Plumbonacrite

Chemical formula: Pb²⁺₅(CO₃)₃O(OH)₂

Plumbonacrite is a rare, secondary lead mineral, forming pearly-white, lamellar aggregates, closely related to hydrocerussite.

## Characteristics Plumbonacrite is a basic lead carbonate, usually occurring as earthy masses or aggregates of small, hexagonal plates and lamellae. Its aggregates often have a silky or pearly luster, and individual crystals are typically too small to be seen with the naked eye. This mineral is soft, heavy, and brittle. Due to its similarity, it is sometimes confused with hydrocerussite, to which it is structurally related. ## Physical Properties Plumbonacrite is characterized by low hardness, approximately 3.5 on the Mohs scale. It has a high specific gravity (about 6.96 g/cm³), which is typical for lead minerals. The luster is most often pearly on cleavage surfaces or silky in the case of fibrous aggregates, and on other surfaces, it can be resinous to vitreous. It is transparent to translucent. ## Colors and Varieties This mineral is most often colorless, white, or grayish. Sometimes it is tinged greenish or yellowish by admixtures or inclusions of other minerals. No named varieties are distinguished. ## History and Name The name plumbonacrite refers to its chemical composition – lead (Latin: *plumbum*) and its appearance resembling mother-of-pearl (*nacre*). It was first described in 1889 by H.F. Collins based on material from the Higher Pitts mine in Somerset, England. For many years, its status as a distinct mineral was questioned, but it was finally confirmed and recognized by the IMA in 1964. ## Uses Plumbonacrite has no industrial significance. However, it is an interesting mineral sought after by advanced collectors of rare minerals, especially specimens with well-formed crystalline aggregates.

Properties

Mohs hardness: 3.5
Color: Colorless to white
Luster: Pearly, Resinous, Vitreous
Streak: White
Density: 7.07
Cleavage: Perfect on {0001}
Fracture: Uneven
Transparency: Transparent,Translucent
Crystal system: Trigonal

Diagnostic features

## Identification Plumbonacrite can be recognized by its characteristic, pearly-white, lamellar or scaly aggregates. Key features include high density (the specimen is surprisingly heavy for its size), low hardness, and reaction with acids (vigorous effervescence). The pearly luster on cleavage surfaces is also an important clue. ## Distinguishing from Similar Minerals Plumbonacrite is visually almost identical to hydrocerussite and cerussite. Distinguishing it from hydrocerussite without advanced analytical methods (such as X-ray diffraction, XRD) is practically impossible. It differs from cerussite in crystal form – cerussite more often forms distinct, vitreous prismatic or tabular crystals, often twinned, while plumbonacrite occurs mainly as fine-scaly, pearly masses. ## Crystal Forms It forms very small, thin, hexagonal tabular or platy crystals. Most often, it occurs as radial or rosette-like aggregates of these crystals, as well as in the form of compact, earthy, or scaly crusts.

Geological environment

## Genesis Plumbonacrite is a secondary mineral, forming in the oxidation (weathering) zones of lead ore deposits. It forms as a result of the alteration of other lead minerals, such as galena or cerussite, under the influence of carbonate-rich waters. It can also form as a product of corrosion of old lead objects (e.g., shipwrecks, pipes) or in mine dumps and metallurgical slags. ## Mineral Associations It often co-occurs with other secondary lead minerals, such as hydrocerussite (with which it is closely related), cerussite, anglesite, as well as with calcite, galena, and sphalerite. ## Localities Important localities worldwide include the Higher Pitts mine in Somerset (type locality) and deposits in Cumbria, England. It is also known from the Grand Reef mine in Arizona and several places in California (USA); from Tsumeb, Namibia; from Laurion, Greece; from mines in the Broken Hill area, Australia; and from numerous localities in Scotland, where it forms on old metallurgical slag heaps.

Rarity

Rare

For collectors

## Quality Criteria Most valued by collectors are specimens with well-formed, visible-to-the-naked-eye crystals forming aesthetic, rosette-like or radial aggregates. A contrasting combination of white plumbonacrite with minerals of other colors (e.g., with dark galena) significantly increases the attractiveness of the specimen. Purity and lack of damage to delicate crystalline structures are also important. ## Popular Localities Specimens of the best quality come from classic localities such as the mines in Cumbria, England, from Laurion, Greece, and from the Grand Reef mine in Arizona, USA. Material from these places is considered the standard for this mineral.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using only a soft brush to remove dust. The use of water is not recommended, as the mineral is sensitive to moisture and may react with chemicals dissolved in water. If necessary, isopropyl alcohol can be used, applied gently and allowed to evaporate quickly. ## What to Avoid Contact with acids (even weak ones, like vinegar) must be strictly avoided, as they cause vigorous effervescence and decomposition of the mineral. Plumbonacrite is very soft and brittle, so it must be protected from impacts, scratching, and vibrations. It should not be heated or exposed to prolonged moisture. ## Storage It is recommended to store specimens in a dry place, in closed, padded collector's boxes, to protect them from dust, mechanical damage, and changes in humidity. Due to its lead content, hands should be washed after handling the mineral.

External references

https://www.mindat.org/min-3229.html