Graftonite

graftonite

triphylite

beusite

sarcopside

Images

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

Pegmatites

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).

Back to Minerals