Nigelcookite

Chemical formula: Pb<sup>2+</sup>Fe<sup>2+</sup><sub>2</sub>V<sup>3+</sup><sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>(OH)<sub>3</sub>

Nigelcookite is an extremely rare phosphate mineral of the palermoite group, forming microscopic, dark brown to black crystals.

## Characteristics Nigelcookite is a very rare, recently discovered mineral belonging to the palermoite group. It occurs as small aggregates, composed of subhedral (partially formed) and anhedral (unformed) grains, whose size does not exceed 150 micrometers. It typically forms dark brown, almost black aggregates with a submetallic luster. ## Physical Properties The hardness of the mineral has not been measured, but it has been calculated to be approximately 4 on the Mohs scale. Its density, also determined by calculation, is 4.43 g/cm³. The mineral is opaque, and its streak is brown. It exhibits weak pleochroism in shades of brown. ## Colors and Varieties The only known color of nigelcookite is dark brown to black. No varieties have been distinguished. ## History and Name The mineral was officially approved by the International Mineralogical Association (IMA) in 2022. Its name honors Professor Nigel John Cook (born 1957), an Australian mineralogist and ore geologist, for his contributions to ore mineralogy. The type locality (locus typicus) is the Patrocínio mine in Ferruginha, Conselheiro Pena, Minas Gerais, Brazil. ## Applications Due to its extreme rarity and microscopic size, nigelcookite has no commercial or industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized systematic collections.

Properties

Mohs hardness
4 (obliczona)
Luster
Sub-metallic
Streak
Brown
Density
4.43 (obliczona)
Cleavage
None
Fracture
Uneven
Transparency
Opaque
Crystal system
Monoclinic

Diagnostic features

## Identification Identification of nigelcookite is impossible without advanced analytical techniques. Due to the microscopic size of the grains, it is necessary to use a scanning electron microscope with EDS or WDS analysis and powder X-ray diffraction (PXRD). A key clue is its occurrence in paragenesis with other rare phosphates in the only known locality. ## Differentiation from Similar Minerals Under a microscope, it can be confused with other dark, opaque co-occurring minerals, such as goethite. Definitive differentiation is only possible based on chemical composition analysis. ## Crystal Forms Nigelcookite forms aggregates composed of subhedral and anhedral crystals up to 150 μm in size. Well-formed, isolated crystals have not been observed.

Geological environment

## Genesis Nigelcookite is a secondary mineral that formed within a phosphate-rich lens located in a quartz vein cutting phyllites. Its formation is likely the result of hydrothermal or weathering processes acting on earlier phosphate minerals. ## Mineral Associations This mineral co-occurs with goethite, anapaite, strengite, variscite, and other yet unidentified phosphates. ## Localities The only confirmed occurrence of nigelcookite in the world is its type locality – the Patrocínio mine, Ferruginha, Conselheiro Pena, in the state of Minas Gerais, Brazil.

Rarity

Extremely rare

For collectors

## Quality Criteria For a microscopic mineral such as nigelcookite, the collector's value of a specimen depends on the abundance of aggregates on the rock matrix and the presence of well-defined, though still microscopic, crystalline clusters. The aesthetics of co-occurring minerals also enhance the specimen's attractiveness. ## Popular Localities Specimens originate exclusively from the discovery site in Minas Gerais, Brazil, and are extremely difficult to obtain, mainly going to research institutions and the most specialized rare mineral collections.

Care and storage

## Cleaning Nigelcookite specimens are typically micromounts, which are very delicate. Cleaning is not recommended. If necessary, a gentle stream of compressed air can be used to remove dust, but extreme caution should be exercised. ## What to Avoid Avoid contact with all chemicals, especially acids, which can damage the mineral. Ultrasonic cleaning, washing in water, and exposing the specimen to sudden changes in temperature and humidity are also not recommended. ## Storage Specimens should be stored exclusively in dedicated "micromount" boxes, protecting them from dust, vibrations, and mechanical damage. Storage under stable room conditions is entirely sufficient.

Sources

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