Ferricoronadite

Chemical formula: Pb²⁺(Mn⁴⁺₆Fe³⁺₂)O₁₆

Ferrocoronadite is a rare lead, manganese, and iron oxide from the hollandite supergroup, forming microscopic, black, metallic crystals.

## Characteristics Ferrocoronadite is a mineral from the hollandite supergroup, being the iron (Fe³⁺) analogue of coronadite. It occurs as very small, prismatic or acicular crystals, rarely exceeding 0.1 mm in length. It typically forms radial or tangled aggregates. It is opaque and black in color. ## Physical Properties Due to the microscopic size of the crystals, most physical properties, such as hardness or density, have not been precisely measured, but only calculated based on crystallographic data. The luster is described as metallic to submetallic. The streak of the mineral is black. ## History and Name The mineral was first described in 1986 by J.E. Post, P.J. Dunn, and B.S. Criddle. Its name refers to its chemical composition – the dominance of iron (Latin: *ferrum*) – and its structural relationship to coronadite. It was approved by the International Mineralogical Association (IMA) as a new mineral (IMA1984-041). The type locality is the Silver Hill mine in Arizona, USA.

Properties

Mohs hardness: 5
Color: Black
Luster: Metallic
Streak: Brownish-black
Density: 5.538
Cleavage: (100)
Fracture: Irregular/Uneven
Transparency: Opaque
Crystal system: Tetragonal

Diagnostic features

## Identification Identification of ferrocoronadite is impossible without advanced analytical techniques. It requires chemical analysis (EDS/WDS) to confirm the presence of lead, manganese, and iron in appropriate proportions, and X-ray diffraction (XRD) to determine the crystal structure. Visually, it appears as black, metallic, microscopic needles. ## Distinguishing from Similar Minerals It can be confused with other black, acicular manganese minerals from the hollandite supergroup, such as coronadite, hollandite, or cryptomelane. Differentiation is based solely on precise chemical composition analysis, particularly the ratio of iron to other cations. ## Crystal Forms It forms very small, elongated crystals with a prismatic or acicular habit. These crystals often occur as radial or haphazardly tangled aggregates.

Geological environment

## Genesis Ferrocoronadite is a secondary mineral, forming in the oxidation zones (iron caps) of polymetallic ore deposits, especially those rich in manganese and lead. It forms under low temperature and pressure conditions as a result of the weathering of primary minerals. ## Mineral Associations At the type locality (Silver Hill mine, Arizona, USA), it co-occurs with minerals such as cerussite, anglesite, hemimorphite, wulfenite, fluorite, quartz, and other manganese oxides. ## Localities This is an extremely rare mineral, identified in only a few locations worldwide. Besides the type locality in Arizona (USA), its occurrence has also been reported in the Aghbar mine in Morocco and in the Olary region of South Australia.

Rarity

Extremely rare

For collectors

## Quality Criteria For such a rare mineral, the main criterion for value is its confirmed presence on the rock matrix. Specimens where ferrocoronadite forms richer, microscopically visible clusters of acicular crystals are more highly valued. Association with other well-formed minerals, such as wulfenite or cerussite, is also important. ## Popular Localities The only source of specimens available on the collector's market is its type locality – the Silver Hill mine in Pima County, Arizona, USA.

Care and storage

## Cleaning Due to the extreme rarity and microscopic nature of specimens, mechanical cleaning is not recommended. If absolutely necessary, compressed air can be used to remove dust. Avoid contact with water and chemicals. ## What to Avoid Avoid all acids and strong bases, which can react with the mineral. Specimens are very brittle and sensitive to mechanical damage. They should not be heated or exposed to ultrasound. ## Storage Ferrocoronadite specimens should be stored exclusively in specialized micromount boxes, protecting them from dust, moisture, and physical damage. Avoid vibrations and shocks.