Perloffite

Chemical formula: BaMn²⁺₂Fe³⁺₂(PO₄)₃(OH)₃

Perloffite is a rare phosphate mineral characterized by its dark brown to black color, occurring as small, radial aggregates.

## Characteristics Perloffite is a complex barium, manganese, and iron phosphate belonging to the bjarebyite group. It forms very small, platy or tabular crystals, which most often occur as radial or spherulitic aggregates. Individual crystals rarely exceed 1 mm in length. Its color is typically dark brown, reddish-brown to almost black, giving it a characteristic, tar-like appearance. ## Physical Properties This mineral has a hardness of 5 on the Mohs scale. It has a vitreous to resinous luster. It is a relatively dense mineral, with a specific gravity of approximately 4.36 g/cm³. It is brittle and exhibits an uneven fracture. ## Colors and Varieties Perloffite occurs in shades from reddish-brown and dark brown to black. No varieties have been distinguished. ## History and Name Perloffite was discovered in the Big Chief mine, in the Glendale area, Pennington County, South Dakota (USA). It was described and approved as a new mineral in 1977. Its name honors Louis Perloff (1913–1999), an American mineral collector from Philadelphia, specializing in microminerals, who first noticed this mineral. ## Uses Due to its rarity and small crystal size, perloffite has no industrial applications. It is solely an object of collector interest, especially for micromineral collectors.

Properties

Mohs hardness
5
Color
Brownish black, green-brown, black
Luster
Vitreous to Resinous
Streak
Greenish yellow
Density
0
Cleavage
on {100}
Fracture
Uneven
Transparency
Transparent
Crystal system
Monoclinic

Diagnostic features

## Identification Perloffite can be identified by its characteristic radial aggregates composed of small, platy crystals with a dark brown to black color and vitreous or resinous luster. It occurs in a specific geological environment – in complex granitic pegmatites. ## Differentiation from Similar Minerals It can be confused with other dark phosphates found in pegmatites, such as arrojadite, graftonite, or members of the wyllieite group. Definitive differentiation requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS), due to visual similarity and co-occurrence with other phosphate minerals. ## Crystal Forms Perloffite crystals are most often platy or tabular, flattened parallel to the {001} plane. They typically form radial, rosette-like, or spherulitic aggregates, as well as granular masses.

Geological environment

## Genesis Perloffite is a secondary mineral that forms in hydrothermal zones or as a result of metasomatic processes in complex, phosphate-rich granitic pegmatites. It forms from the alteration of earlier phosphate minerals. ## Mineral Associations This mineral co-occurs with other pegmatitic phosphates. In its type locality (Big Chief mine, South Dakota, USA), it was found in association with minerals such as satterlyite, goethite, rockbridgeite, strengite, and quartz. In other localities, it is accompanied by, among others, jahnsite-(CaMnFe), mitridatite, ludlamite, and vivianite. ## Localities The most important and confirmed occurrences of perloffite are: - **USA**: Big Chief mine in South Dakota (type locality) and Palermo No. 1 mine in New Hampshire. - **Germany**: Hagendorf-Süd in Bavaria. - **Brazil**: Sapucaia in Minas Gerais. - **Rwanda**: Buranga mine in Western Province.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, radial aggregates of intense, dark color, contrasting with a lighter matrix. Given that perloffite is a typical micromineral, the quality and sharpness of individual crystals visible under magnification are crucial. The size of the aggregates and the richness of associations with other rare phosphates also significantly increase the value of a specimen. ## Popular Localities Specimens from the type locality, the Big Chief mine in South Dakota, have particular historical value. High-quality microminerals also come from Hagendorf, Germany, and the Palermo mine in New Hampshire.

Care and storage

## Cleaning Perloffite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its brittleness and small crystal size, ultrasonic cleaners and mechanical cleaning should be avoided. If liquid is necessary, distilled water is recommended. ## What to Avoid Contact with acids and strong chemical agents, which can damage the mineral, should be avoided. It should not be heated or exposed to sudden temperature changes. ## Storage Perloffite specimens, especially those in the form of micromounts, should be stored in sealed "micromount" boxes that protect them from dust, mechanical damage, and moisture. Exposure to direct sunlight should be avoided, although there is no evidence of fading.

External references

Sources

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