Ferrobobfergusonite

Chemical formula: &#₉₇₄₄;Na₂Fe₂+₅Fe₃+Al(PO₄)₆

Ferrobobfergusonite is a very rare, dark green to black phosphate mineral, named after the Canadian mineralogist Robert Ferguson.

## Characteristics Ferrobobfergusonite is a complex sodium, iron, and aluminum phosphate belonging to the alluaudite group. It forms elongated, lath-like crystals, usually not exceeding 1 mm in size, which often occur in radial or tangled aggregates. The mineral is opaque and has a dark green, greenish-black, or almost black color. ## Physical Properties Crystals exhibit a vitreous luster. The Mohs hardness is approximately 4, and the density is estimated at 3.65 g/cm³. The mineral is brittle and characterized by an uneven fracture. No fluorescence has been observed under ultraviolet light. ## History and Name The mineral was approved by the IMA in 2017. Its name honors Robert Bury Ferguson (1920-2015), a Canadian mineralogist and crystallographer from the University of Manitoba, in recognition of his contributions to mineralogy. The prefix "ferro-" refers to the dominance of divalent iron (Fe²⁺) in its chemical composition, which distinguishes it from other minerals in this series.

Properties

Mohs hardness: 4
Luster: Vitreous
Streak: Greenish-gray
Density: 3.65
Cleavage: Good on {100}
Fracture: Uneven
Transparency: Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of ferrobobfergusonite requires advanced analytical methods, such as Raman spectroscopy or chemical analysis using an electron microprobe (EDS/WDS). Visually, it is difficult to distinguish from other dark associated minerals. Its characteristic lath-like habit and occurrence in granitic pegmatites are distinctive. ## Distinguishing from Similar Minerals It can be confused with other minerals from the alluaudite group, such as bobfergusonite or alluaudite, as well as with dark tourmalines (schorl) or arfvedsonite, with which it co-occurs. Definitive differentiation is possible only through chemical analysis, which will show the dominance of Fe²⁺. ## Crystal Forms It forms prismatic, lath-like crystals, elongated along the c-axis, up to 1 mm in length. These crystals group into radial or randomly oriented aggregates.

Geological environment

## Genesis Ferrobobfergusonite is a magmatic mineral, crystallizing in the late stages of the evolution of complex granitic pegmatites, rich in phosphates. It forms in zones with highly differentiated chemical composition. ## Mineral Associations This mineral co-occurs with quartz, microcline, albite, arfvedsonite, schorl, as well as other rare phosphates such as beusite, fillowite, and galileiite. ## Localities The only confirmed locality of ferrobobfergusonite in the world (type locality) is the "Pod Pegmatytem" granite quarry near the town of Piława Górna in Lower Silesia, Poland.

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, its collector value depends on the quality and development of the crystals, rather than their size. Specimens with well-defined, undamaged crystals forming aesthetic aggregates, clearly contrasting with the matrix rock, are most prized. The presence of associated minerals is also important. ## Popular Localities The only source of specimens is the type locality in Piława Górna, Poland, which makes every specimen from this location unique.

Care and storage

## Cleaning Due to its brittleness and rarity, mechanical cleaning is not recommended. If necessary, compressed air can be used to remove dust. Contact with water and chemical agents should be avoided. ## What to Avoid Avoid ultrasonics, steam cleaners, and all acids and solvents, which can damage or destroy delicate crystals. The mineral is sensitive to shocks and impacts. ## Storage Ferrobobfergusonite specimens should be stored under stable conditions, in a sealed "micromount" box, protected from dust, moisture, and mechanical damage. Avoid exposure to direct sunlight and sudden temperature changes.

Sources

IMA Mineral List (CNMNC)