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Formula: Zn2Fe3+3(PO4)3(OH)4(H2O)
Hydrated phosphate, rockbridgeite group,
zinc-bearing mineral
Crystal system: Orthorhombic
Specific gravity: 3.67 measured, 3.62 calculated for the empirical formula
Hardness: 3½ to 4
Streak: Pale greyish green
Colour: Pale green to dark olive-green, almost black
Luminescence: No observable fluorescence under UV
Environments
Metamorphic environments
Hydrothermal environments
Plimerite is a secondary mineral occurring in the
weathering zone in seams and cavities of quartz -
garnet - goethite rich rock
(HOM).
Localities
The type locality is the Block 14 opencut, Broken Hill, Broken Hill district, Yancowinna County, New South Wales,
Australia. The region has undergone multiphase metamorphism and deformation to
granulite and
upper amphibolite facies. A long and complex history
of weathering has resulted in an extensive oxidised zone, which is notable for the complexity of its mineralogy.
The phosphate suites are derived from weathering of
primary
fluorapatite, which is a common accessory mineral in the sulphide
orebody.
The following paragenesis for the suite of secondary phosphate
minerals has been proposed:
corkite–hinsdalite →
turquoise–chalcosiderite
→ leucophosphite →
dufrenite/rockbridgeite
→ kidwellite →
beraunite →
sampleite/strengite →
torbernite.
Plimerite-zincian
rockbridgeite is found in seams and cavities in
quartz - garnet -
goethite rich rocks from the Block 14 Opencut. On the type specimen,
plimerite is associated with crusts of white to yellow
hinsdalite-plumbogummite,
white prisms of calcian pyromorphite, sprays of pale green
libethenite prisms, greenish-blue
brochantite crystals and aggregates of acicular
malachite crystals. On other specimens, additional associated minerals
are greenish-blue crystals of tsumebite and hemispherical aggregates of
pinkish white strengite crystals.
Plimerite occurs as pale-green to dark olive-green hemispherical aggregates of radiating acicular crystals,
and less commonly as pale olive-green to dark green, almost black, acicular to elongated, bladed and prismatic
crystals, which are found as individual crystals but more typically as radiating sprays and hemispherical
aggregates. The maximum length of crystals is 0.5 mm and hemispherical aggregates can reach up to about 3 mm across.
Plimerite is translucent with a pale greyish green streak and a vitreous lustre
(MM 73.1.131-148).
Plimerite from the Block 14 opencut -
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At Reaphook Hill, Martins Well, Pastoral Unincorporated Area, South Australia, Australia, plimerite occurs as
green- to greenish-yellow crystal aggregates and druses, and is associated with
scholzite, parahopeite,
collinsite–hillite and
eosphorite
(MM 73.1.131-148).
Plimerite from Reaphook Hill -
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At the Huber stock, Krásno, Sokolov District, Karlovy Vary Region, Czech Republic, plimerite samples have
been found at supergene altered phosphate accumulations in
the abandoned Huber open pit. The plimerite was found in cavities of strongly altered original
triplite accumulations in the following five morphological types:
Plimerite type 1 forms abundant semi-spherical to spheroidal radiating aggregates up to 1.5 mm in size,
locally clustering to aggregates up to 2 mm, in association with light yellow-grey imperfect crystals of young
fluorapatite. They occur in cavities (1–2 mm across) of
triplite aggregates, altered to compact red-brown
fluorapatite and isokite.
This material is accompanied by coarse-grained white quartz containing
grains (up to 2 cm) of dark green fluorapatite. The plimerite
type 1 aggregates are black-green to black with a green hue, vitreous on fracture, with a greasy lustre. Its minute
splinters are transparent, bright green, and have a light grey-green streak. The surface of the aggregates consists
of intergrown tabular crystals 20 to 40 μm long, oriented perpendicular to the surface of the spherical aggregates.
Plimerite type 2 has been found in strongly altered aggregate of pinkish and white
fluorapatite, 7 by 10 cm in size. Plimerite forms soft and
crumbly olive to grey-green aggregates up to 2 cm across, deposited in irregular cavities in
fluorapatite 5 by 6 cm in size. These aggregates consist of minute
well-formed crystals up to 100 μm long in association with frequent white to light green
fluorapatite and less abundant greyish white
kolbeckite aggregates. Individual tabular crystals of plimerite
are green to black with a green hue and have a vitreous lustre.
Plimerite type 3 occurs in weathered vugs (2 by 3 cm in size) in
fluorapatite/isokite
accumulations with triplite relics. It forms dark green crystalline
aggregates 0.5 to 1 mm across, composed of tabular crystals up to 0.1 mm long. Plimerite aggregates with a
strong vitreous lustre, showing occasional rhombic cross- sections, are usually overgrown by zoned aggregates of
minerals of the turquoise group,
pharmacosiderite, rare
kolbeckite and chlorine-rich
fluorapatite. Kunatite,
leucophosphite,
whitmoreite and
earlshanonnite were also observed in this association.
Plimerite type 4 forms microscopic (up to 30 μm) irregular inclusions in acicular to fibrous
zinc- and aluminium-rich
beraunite associated with
fluorapatite and irregular crystals and aggregates of potassium-poor
leucophosphite
Plimerite type 5 was found as irregular aggregates up to 100 μm in size, which (with
whitmoreite) replace older aggregates of
isokite and fluorapatite
(Journal of GEOsciences 56.2.215-229).
Plimerite from the Huber Stock -
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