Bacaferrite

Chemical formula: BaCaFe<sup>3+</sup><sub>4</sub>O<sub>8</sub>

Bacaferrite is an extremely rare barium, calcium, and iron oxide, forming microscopic, black crystals with a metallic luster.

## Characteristics Bacaferrite is an oxide mineral that visually presents as opaque, black crystals with a strong metallic luster. It typically forms very small, bladed or tabular crystals, not exceeding 0.2 mm in length. These crystals often occur as radial aggregates or small rosettes on the surface of the host rock, which is hematite. ## Physical Properties This mineral is opaque. Its Mohs hardness has not been determined. The density calculated based on its chemical composition and unit cell parameters is 4.96 g/cm³. It exhibits good cleavage in one direction. ## Colors and Varieties Bacaferrite occurs exclusively in black. No color or commercial varieties are known. ## History and Name The mineral was first described in 1998 by S.J. Mills, W.D. Birch, U. Kolitsch, and W.G. Mumme. Its name refers to its chemical composition, dominated by barium (Ba), calcium (Ca), and iron (Latin: *ferrum*, Fe). The type locality, which is the only confirmed occurrence, is the Iron Monarch mine in South Australia. ## Uses Due to its extreme rarity and microscopic size, bacaferrite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized micromount collectors.

Properties

Luster
Metallic
Streak
Black
Density
4.96
Cleavage
Good on {010}
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Characteristic features of bacaferrite include its black color, strong metallic luster, and the form of small, bladed crystals forming radial aggregates. Its occurrence on a hematite matrix at the only known locality in the world is also crucial. Definitive identification is only possible using advanced analytical methods, such as X-ray microanalysis (EDS/WDS). ## Distinguishing from Similar Minerals Bacaferrite can be confused with other black minerals with a metallic luster, such as fine-grained hematite or goethite. Distinguishing it with the naked eye or under a magnifying glass is practically impossible. Chemical composition and crystal structure analyses are decisive. ## Crystal Forms The mineral forms elongated, bladed or flattened, tabular crystals. They often coalesce into small, radial aggregates resembling rosettes.

Geological environment

## Genesis Bacaferrite forms under high-temperature conditions in highly oxidized, metamorphosed iron formations. Its genesis is likely associated with fumarolic activity, i.e., exhalations of hot volcanic gases rich in various elements. ## Mineral Associations This mineral occurs in direct association with hematite (which is the host rock), baryte, and another unnamed barium-iron oxide. ## Localities The only confirmed and described occurrence of bacaferrite in the world is the Iron Monarch open-pit iron ore mine, located in the Iron Knob region on the Eyre Peninsula in South Australia.

Rarity

Extremely rare

For collectors

## Quality Criteria The quality of bacaferrite specimens, being a mineral for micromount collectors, is assessed based on several criteria. Specimens with well-formed, sharp, and undamaged crystals are most highly valued. Their attractive arrangement on the rock matrix, forming aesthetic rosettes or rich aggregates, is important. Contrast with the surrounding hematite also enhances the visual value of the specimen. ## Popular Localities The only source of bacaferrite specimens is its type locality – the Iron Monarch mine in South Australia. All specimens available on the collector's market originate from this single location.

Care and storage

## Cleaning Bacaferrite specimens are extremely small and fragile, so mechanical or chemical cleaning is not recommended. Any attempts may lead to irreversible damage to the crystals. If necessary, dust can be carefully removed with a stream of compressed air from a safe distance. ## What to Avoid Contact with any chemicals, acids, and detergents must be strictly avoided. The mineral is sensitive to shocks and abrasions. Do not use ultrasonic cleaners. Store away from sources of moisture. ## Storage It is recommended to store specimens exclusively in specialized, sealed micromount boxes. This protects the delicate crystals from dust, mechanical damage, and changes in ambient humidity.

Sources

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