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Formula: Fe2+Fe2+2(PO4)2
Anhydrous normal phosphate, graftonite group, forms a series with
beusite, epitaxial intergrowths with
triphylite
Specific gravity: 3.67 to 3.79 measured, 3.95 calculated
Hardness: 5
Streak: White to faintly pink, when unaltered
Colour: Usually reddish brown, occasionally light brown, rarely salmon-pink, may be dark brown due to alteration; nearly
colourless in transmitted light
Luminescence: Not fluorescent in UV
Solubility: Readily soluble in acids
Environments
Graftonite is a primary phosphate mineral found in complex
granitic
pegmatites. Common associates include
albite,
heterosite, muscovite,
quartz and triphylite
(Mindat).
Localities
At the pegmatites at Bernic Lake, Lac-du-Bonnet area, Manitoba,
Canada, in atypical members of the
beryl-columbite-phosphate subtype,
homogeneous calcium-rich beusite is
manganese-dominant and associated with
manganese-bearing fluorapatite
and traces of triplite and
triphylite.
Low activities of sodium,
lithium and fluorine,
combined with high concentrations of calcium, iron,
manganese (and locally magnesium), are required to stabilise
graftonite-beusite. These conditions cannot be expected to be widespread
in the rare-element pegmatites of the Superior Province, as most
of them show early enrichment in lithium and fluorine. Consequently,
graftonite-beusite is not stable, as
triphylite-lithiophilite tends
to be a relatively early phase, and fluorapatite consumes all
phosphate-bound calcium
(CM 36.2.367-376).
At Cross Lake, Manitoba, Canada, in the #22 pegmatite, of the
beryl-columbite-phosphate subtype,
homogeneous calcium-poor beusite shows the most
manganese-rich composition known to date, and is associated with similarly
manganese-rich fillowite,
fluorapatite and triploidite,
plus two unidentified phosphates.
Low activities of sodium, lithium and fluorine,
combined with high concentrations of calcium, iron,
manganese (and locally magnesium), are required to stabilise
graftonite-beusite. These conditions cannot be expected to be widespread
in the rare-element pegmatites of the Superior Province, as most
of them show early enrichment in lithium and fluorine. Consequently,
graftonite-beusite is not stable, as
triphylite-lithiophilite tends
to be a relatively early phase, and fluorapatite consumes all
phosphate-bound calcium
(CM 36.2.367-376).
At Conifer Road, Campfire Lake, Kenora District, Ontario, Canada, in the
granulite facies terrane, a geochemically primitive,
barren pegmatite carries graftonite with inclusions of
scandium-bearing, magnesium-rich johnsomervilleite and exsolved
sarcopside lamellae.
Low activities of sodium, lithium and fluorine,
combined with high concentrations of calcium, iron,
manganese (and locally magnesium), are required to stabilise
graftonite-beusite. These conditions cannot be expected to be widespread
in the rare-element pegmatites of the Superior Province, as most
of them show early enrichment in lithium and fluorine. Consequently,
graftonite-beusite is not stable, as
triphylite-lithiophilite tends
to be a relatively early phase, and fluorapatite consumes all
phosphate-bound calcium
(CM 36.2.367-376).
At the Bothnian basin and the Uto-Mysingen field in Sweden,
graftonite-beusite is relatively widespread in the LCT
(lithium, cesium,
tantalum) family of
granitic
pegmatites. It commonly constitutes the matrix containing
either coarse lamellae of sarcopside, which in turn hosts fine lamellae of
triphylite, or abundant lamellae of
triphylite. Deformed and recrystallized granular aggregates of
graftonite with triphylite,
wolfeite and sarcopside are rare.
Graftonite-beusite is systematically calcium- and
manganese- rich and magnesium-poor relative to
sarcopside, which in turn is slightly
manganese-rich and distinctly magnesium-poor relative to the
lithium-concentrating triphylite.
Two patterns of exsolution that generated the lamellar intergrowths from disordered homogeneous precursors are indicated:
(1) Calcium- and lithium- poor graftonite exsolved
lithium-rich sarcopside, which in
turn broke down to sarcopside with
triphylite lamellae, and
(2) Calcium-, lithium-,
(manganese-) rich
graftonite-beusite exsolved
triphylite directly.
In regional zoning of pegmatite groups, calcium-bearing
graftonite-beusite is either the first
iron-, manganese-, (lithium-)
phosphate encountered in the
beryl-columbite
pegmatites, or it is found within the zone of
beryl-columbite-triphylite
pegmatites. Appreciable concentrations of calcium,
iron, manganese (and in part magnesium),
but low levels of fluorine and sodium, are required to stabilise
graftonite-beusite. Indications are that the homogeneous
graftonite-beusite precursor could have been generated by
phosphorus-induced destabilisation of garnet
(CM 36.377-394).
At the Waisanen Quarry, Greenwood, Oxford County, Maine, USA, in a
pegmatite, a specimen was found of massive graftonite,
about 2.5 x 2 x 1.5 cm, showing no crystal faces. On one side is a compact assemblage of
quartz, albite,
muscovite, chlorite,
calcite, pyrite,
sphalerite and arsenopyrite,
with an occasional grain of triphylite
(AM 22.1035-1039).
At the type locality, Melvin Mountain, Grafton, Grafton County, New Hampshire, USA, in a complex
granite
pegmatite, graftonite is
irregularly disseminated through a coarse crystalline mass of quartz and
feldspar, the feldspar individuals
being up to four feet long. Minerals associated with graftonite included
beryl, schorl,
almandine, muscovite and
biotite, all crystallised on a rather large scale, especially the
beryl
(The American Journal of Science 159.20-32).
At the Palermo mica mine, Groton, Grafton County, New Hampshire, USA, the
granite
pegmatite from which mica
was mined for many years is intruded in schist. The specimens present a
striking appearance due to the large number of bands of clear brown graftonite alternating with deep purple
heterosite, an alteration product of
triphylite. The graftonite bands, which do not exceed 4 mm in width,
are, as a rule, wider than the bands of heterosite. The minerals found in
association with graftonite were muscovite,
biotite, almandine coated with a
uranium mineral, and a few small
zircon crystals. The pocket in which the graftonite occurred seems to have
been lined with muscovite and
biotite in which zircon and
almandine crystals are embedded. Most of the specimens also contain
considerable amounts of triphylite without graftonite. One specimen
was essentially triphylite with narrow bands of
vivianite throughout the mass. There are also
pyrite cubes, pyrrhotite and some
chalcopyrite distributed in the
triphylite, all of which are somewhat oxidised
(AM 12.170-172).
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.
Graftonite has been reported from the middle intermediate zone of the Keyes No. 1
pegmatite, and it also occurs at the No. 2 mine. Keyes
graftonite typically is pinkish-brown and laminated, and associated with
triphylite and vivianite. It has
been found in masses to 9 cm
(R&M 97.4.318).
At the Parker Mountain mine, Parker Mountain, Strafford, Strafford County, New Hampshire, USA, in
pegmatites, graftonite occurs in small reddish brown
intergrowths with triphylite
(AM 23.814-815).
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