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Formula: Fe3+(PO4).2H2O
Hydrated phosphate, metavariscite group,
paramorph of
strengite
Crystal System: Monoclinic
Specific gravity: 2.74 to 2.76 measured, 2.72 calculated
Hardness: 3½ to 4
Streak: White
Colour: Purple to reddish violet, rose-red, peachy-pink, brownish yellow, moss-green, colourless; rose to colourless in
transmitted light.
Solubility: Totally soluble in hydrochloric acid, nearly insoluble in nitric acid (Mindat)
Common impurities: Al,Mn
Environments:
Phosphosiderite is typically an alteration product of triphylite in zoned complex
granite pegmatites;
it also may be a component of soils, replacing bones or shells.
Associated minerals include triphylite,
barbosalite, leucophosphite,
laueite, hureaulite,
strengite and turquoise
(HOM).
Localities
At the phosphate deposits of South Australia, phosphosiderite is associated with
variscite,
quartz and leucophosphite
(AJM 17.1.25).
Phosphosiderite from South Australia - Image
At the type locality, the Kalterborn Mine, Eiserfeld, North Rhine-Westphalia, Germany, phosphosiderite occurs in
iron ore (Dana).
At the Keyes Mica Quarries, Orange, Grafton County, New Hampshire, USA, the
pegmatites are beryl-type
rare-element (RE) pegmatites.
The Number 1 mine exposed a pegmatite that shows the most
complex zonation and diverse mineralogy of any of the Keyes
pegmatites. Six zones are distinguished, as follows, proceeding
inward from the margins of the pegmatite:
(1) quartz-muscovite-plagioclase
border zone, 2.5 to 30.5 cm thick
(2) plagioclase-quartz-muscovite
wall zone, 0.3 to 2.4 metres thick
(3) plagioclase-quartz-perthite-biotite
outer intermediate zone, 0.3 to 5.2 metres thick, with lesser muscovite
(4) quartz-plagioclase-muscovite
middle intermediate zone, 15.2 to 61.0 cm thick
(5) perthite-quartz inner intermediate zone, 0.9 to 4.6 meters thick
(6) quartz core, 1.5 to 3.0 metres across
The inner and outer intermediate zones contained perthite crystals up to
1.2 meters in size that were altered to vuggy
albite-muscovite with
fluorapatite crystals. This unit presumably was the source of the
albite, muscovite,
fluorapatite, quartz and other
crystallised minerals found in pieces of vuggy albite
rock on the dumps next to the mine.
The middle intermediate zone produced sheet mica with accessory minerals including
tourmaline, graftonite,
triphylite, vivianite,
pyrite, pyrrhotite, and
beryl crystals to 30.5 cm long and 12.7 cm across.
Phosphosiderite occurs here associated with rockbridgeite
(R&M 97.4.322).
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