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Formula: PbFe2+2V3+2(PO4)3(OH)3
Phosphate, bjarebyite group,
vanadium-bearing mineral
Crystal system: Monoclinic
Specific gravity: 4.57 calculated
Hardness: 4 to 5
Colour: Dark brown to greenish brown
Environments
Volcanic igneous environments
Hydrothermal environments
Localities
At the type locality, Yushui Mine, Mei County, Meizhou, Guangdong, China, nigelcookite and
plumbojohntomaite occur in the bedded/massive
copper ore, and often occur in association with
chalcopyrite, galena,
sphalerite, nolanite,
pyrite, anhydrite,
apatite, fluorite,
xenotime-(Y) and quartz. They
are both members of the bjarebyite group.
Nigelcookite occurs as spearhead-shaped or platy crystals ranging from 5 to 100 μm in size, and
plumbojohntomaite occurs as platy crystals ranging from 5 to
80 μm in size. Both minerals are translucent to transparent with vitreous lustre, but they differ in colour.
Nigelcookite ranges from dark brown to greenish brown, while
plumbojohntomaite varies from dark green to olive green.
Indications are that there is isomorphic substitution between V3+ and Fe3+ in
nigelcookite and plumbojohntomaite respectively. Given the
occurrence of Fe3+ in plumbojohntomaite, its formation
condition is more oxidised than that of nigelcookite
(AM 110.10.1614-1625).
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