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Formula: Fe2+Sn4+Ta2O8
Oxide, wodginite group,
columbite supergroup,
tantalum- and tin- bearing mineral
Crystal System: Monoclinic
Specific gravity: 7.02 calculated
Hardness: 5½
Streak: Dark brown
Colour: Dark brown to black
Luminescence: Not fluorescent under UV
Common impurities: Mn,Ti,Nb
Environments
Localities
At the Sierra de la Estanzuela, Chacabuco Department, San Luis Province, Argentina, in the San Elias
pegmatite
ferrotitanowodginite occurs aggregated with
ferrowodginite and associated with microlite,
ferrotapiolite
cleavelandite and quartz. In La
Viquita pegmatite,
ferrotitanowodginite occurs in a replacement unit associated
with wodginite, ferrowodginite,
titanowodginite and
tapiolite-(Fe) in yellow
muscovite and quartz
(AM 84.773–777).
Ferrowodginite from the Sierra de la Estanzuela
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At the Separation Rapids Lithium Project, Kenora District, Ontario, Canada, ferrowodginite has been found in
the beryl zone and in the
petalite zone.
In the beryl zone three occurrences of
wodginite group minerals have been investigated:
(i) ferrowodginite from a dyke of garnetiferous
aplite close to the margin of the Separation Rapids pluton
(ii) ferrowodginite from a fluorapatite -
garnet - biotite -
muscovite potassic
pegmatite in close proximity to the
petalite zone
(iii) wodginite (ss) from a layered 8 m thick
fluorapatite - garnet
- biotite - muscovite potassic
pegmatite containing platy
albite-rich pods with purple
lithian muscovite, white
beryl, tourmaline,
cassiterite,
columbite-(Mn) and (almost end-member)
tantalite-(Mn).
In the petalite zone in
petalite-bearing
pegmatites, the greatest variety of
wodginite group minerals has been found, with ferrowodginite
by far the most widespread. Cassiterite is the oxide mineral most
commonly found with the wodginite group minerals, and in some
samples, the wodginite occurs only as inclusions in
cassiterite grains.
Columbite and tantalite are
also found in most wodginite-bearing samples. In order of increasing
rarity, other oxide phases include microlite,
uraninite,
fluornatromicrolite,
oxystibiomicrolite and
strüverite. The oxide assemblages, however, are abundant only in
primary albite-rich
units or secondary
beryl - muscovite -
albite assemblages that variably replace the central
petalite-rich core of some
pegmatite bodies.
Concentrations of niobium -
tantalum - tin oxides (such as
ferrowodginite) are commonly associated with fluorapatite.
Ferronigerite-2N1S,
chalcopyrite,
arsenopyrite, löllingite,
thorian monazite,
xenotime and zircon occur less
frequently. Tourmaline and
garnet may also be present, the latter locally abundant in outer,
earlier-crystallised units.
Ferrowodginite is opaque and occurs as isolated grains associated with
albite and apatite or as
inclusions within cassiterite grains
(CM 36.2.637–658).
At the type locality, the Sukula Pegmatites, Tammela, Kanta-Häme, Finland, ferrowodginite occurs in the
granitic
pegmatite. Samples consist predominantly of granular
aggregates of strongly colour-zoned tantalum-bearing
cassiterite, with individual grain-sizes ranging from 1 mm to a few cm.
Tapiolite, native bismuth and
ferrowodginite occur as inclusions in the cassiterite.
Oxystannomicrolite occurs as a replacement of the
ferrowodginite.
The ferrowodginite inclusions in cassiterite are typically 0.01
to 0.2 mm long; however, grains as large as 0.3 mm have been found.
Oxystannomicrolite rims about the ferrowodginite
inclusions are
typically of the order of 10 microns thick. Ferrowodginite is dark brown to black and has a dark brown
streak. It is transparent to translucent, non-fluorescent, and has a vitreous lustre.
(CM 30.3.633-638).
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