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Formula: Ca2Mn2+(PO4)2.2H2O
Hydrated phosphate, fairfieldite group, forms a series with
collinsite,
manganese-bearing mineral
Crystal System: Triclinic
Specific gravity: 3.08 to 3.11 measured, 3.095 calculated
Hardness: 3½
Streak: White
Colour: White, greenish white, light amber, salmon-yellow; colourless in transmitted light
Solubility: Soluble in acids
Environments
Fairfieldite is an accessory mineral in granite
pegmatites, associated with apatite, strunzite,
diadochite, dickinsonite,
stewartite, rockbridgeite,
mitridatite, hureaulite,
eosphorite, other iron-manganese phosphates,
jahnsite, rhodochrosite,
quartz and muscovite
(HOM ). It is found as an alteration product of dickinsonite and as
pseudomorphs after rhodochrosite
(Mindat, Dana).
Localities
At the type locality, the Fillow Quarry, Branchville, Redding, Fairfield County, Connecticut, USA, fairfieldite occurs in
a granite pegmatite associated with triploidite,
reddingite, lithiophilite,
fillowite, eosphorite and
dickinsonite-(KMnNa)
(Mindat, Dana).
At Berry quarry, Poland, Androscoggin county, Maine, USA, fairfieldite is found with
rhodochrosite, eosphorite,
reddingite and other manganese phosphates
(Dana).
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, fairfieldite is associated with
hureaulite, vivianite and
mitridatite
(R&M 94.6.507).
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.
Fairfieldite was found in a vug containing microsized blue to white
fluorapatite and white crystals of probable
gordonite
(R&M 97.4.315).
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