Coronadite

Chemical formula: Pb₂+(Mn₄+₆Mn₃+₂)O₁₆

Coronadite is a lead manganese oxide, forming characteristic fibrous, radial, or massive aggregates of black color and metallic luster.

## Characteristics Coronadite is a mineral from the hollandite group, belonging to the oxide class. Its name comes from its discovery location in Arizona. It forms aggregates of varied morphology – from fine-grained and earthy masses, through reniform and botryoidal forms, to radial or tangled fibrous aggregates. It rarely occurs as small, poorly formed acicular or columnar crystals. It is an opaque mineral, black or dark gray in color. ## Physical Properties Coronadite is characterized by a hardness of 4.5-5 on the Mohs scale and a relatively high density, ranging from 5.2 to 5.7 g/cm³. Its luster is described as metallic to submetallic, becoming dull on weathered surfaces. It is brittle, and its fracture is uneven. ## Colors and Varieties This mineral is usually black, steel-gray, or dark gray. No colorful varieties or trade names are distinguished. Differences in appearance result mainly from the form of aggregates in which it occurs. ## History and Name The name coronadite was given to the mineral in 1905 by Waldemar Lindgren and William Hillebrand. They honored the Spanish conquistador Francisco Vásquez de Coronado, who led an exploratory expedition in the 16th century in what is now the southwestern United States. The mineral was first identified from samples originating from the Horseshoe and Commercial mines in the Clifton-Morenci district in Arizona, USA. ## Uses Coronadite, due to its lead and manganese content, can be a minor component of local ores of these metals. However, it has no significant industrial application. For collectors, well-formed, radial aggregates are primarily of interest.

Properties

Mohs hardness: 4.5-5
Luster: Sub-metallic
Streak: Black, Brownish-black
Density: 5.2-5.7
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Coronadite can be identified by its black color, metallic or submetallic luster, and relatively high density. Its characteristic forms of occurrence are radial, fibrous aggregates, reniform aggregates, or massive forms. A black or dark brown streak is also an important diagnostic feature. ## Distinguishing from Similar Minerals Coronadite is often confused with other black manganese oxides, such as hollandite, cryptomelane, or pyrolusite. Distinguishing it from hollandite and cryptomelane, with which it forms solid solutions, is often impossible without advanced analyses (e.g., XRD, EDS). It differs from pyrolusite by slightly greater hardness (pyrolusite is very soft and soils fingers) and often a different form of aggregates. Romanechite is also very similar but usually forms botryoidal aggregates with a smoother surface. ## Crystal Forms Well-formed crystals are rare and appear as small, acicular or prismatic forms, often creating radial rosettes. It is most commonly found as fibrous, radial, reniform, botryoidal aggregates, as well as in earthy or compact masses.

Geological environment

## Genesis Coronadite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits, especially those containing manganese and lead. It forms as a result of the alteration of primary manganese minerals (e.g., alabandite) and lead minerals (e.g., galena) under low-temperature and low-pressure conditions. It can also form in low-temperature hydrothermal processes. ## Mineral Associations It often co-occurs with other manganese oxides, such as hollandite, pyrolusite, romanechite, and cryptomelane. It is also accompanied by lead minerals, such as cerussite, anglesite, and mimetite, as well as quartz, barite, fluorite, and iron oxides (goethite, hematite). ## Localities Important global localities include historical sites in Arizona (USA), from which the first described specimens originated. Significant occurrences have also been noted in Broken Hill, New South Wales (Australia), where it forms beautiful radial aggregates. Other known localities include Morocco (e.g., Bou Azzer), Namibia (Tsumeb), Kazakhstan, as well as various places in Europe, including Germany and the United Kingdom.

Rarity

Not very common

For collectors

## Quality Criteria The most prized coronadite specimens by collectors are those forming well-defined, radial aggregates of acicular crystals, resembling "sea urchins" or "sunbursts." The larger the diameter of such an aggregate and the better the formation of individual "needles," the higher the value. Specimens with a contrasting matrix or in association with other colorful secondary minerals (e.g., mimetite) are also attractive. Massive, earthy, or compact forms have significantly lower collector value. ## Popular Localities Historical localities in Broken Hill, Australia, are considered classic and provide the best specimens. Many museum-quality radial aggregates originate from there. Some localities in Morocco also provide aesthetic specimens. Specimens from the type locality in Arizona (USA) are mainly of historical significance.

Care and storage

## Cleaning Coronadite specimens should be cleaned very carefully, preferably dry, using a soft brush to remove dust. If necessary, a damp cloth or cotton swab with distilled water can be used, immediately drying the specimen. Avoid washing under running water, and especially avoid using ultrasonic cleaners, which can damage delicate, fibrous aggregates. ## What to Avoid Coronadite is sensitive to acids, which can damage it. Contact with household and laboratory chemicals should be avoided. As a lead-containing mineral, dust generated during its processing or cleaning is toxic – avoid inhaling it and wash hands after contact with raw, dusty specimens. ## Storage Coronadite specimens, especially those with a delicate, fibrous structure, should be stored in separate, padded boxes to prevent mechanical damage and abrasions. It does not require special conditions regarding light or humidity, but it should be protected from dust and extreme conditions.

External references

https://en.wikipedia.org/wiki/https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FCoronadite