Images
Formula: (Ca,Y,Dy)2Y(WO4)2(AsO4)
Tungstate, arsenic-,
yttrium- and dysprosium-
bearing mineral
Crystal system: Tetragonal
Specific gravity: 5.95 calculated
Colour: Cream-yellow
Luminescence: Moderately strong yellow-orange fluorescence under short wave UV, not fluorescent at 366 nm
Environments
Metamorphic environments
Hydrothermal environments
Localities
At the type locality, the Monte Cervandone area, Devero Alp, Baceno, Verbano-Cusio-Ossola Province, Piedmont, Italy,
paraniite-(Y) was discovered on the Italian side in a fissure in
gneiss in an area anomalously high in
arsenic. Crystals are creamy yellow and show a tetragonal-bipyramidal
habit, closely resembling scheelite. Like
scheelite, they strongly fluoresce orange-yellow. Crystals reach a maximum
size of about 2 mm
(MinRec 56.3.318, HOM).
At Fianel, Ausserferrera, Ferrera, Viamala Region, Grisons, Switzerland, polyphase metamorphism led to the formation
of quartz-dolomite veinlets
containing beryl,
scheelite-powellite,
paraniite-(Y), monazite-(Ce),
fluorapatite, bergslagite
and fluorcalcioroméite (?); these
veinlets crosscut dolomite
breccia lenses that are embedded in
hematite-quartz carbonate ores.
Scheelite-powellite
displays a continuous range of compositions between 28 and 70 mol% CaMoO4. The
scheelite-powellite grains
display a two-stage chemical zoning: stage A generally produced a core and a rim that, relative
to the core, is richer in W, As, and Y than the core. During stage B, W-rich
scheelite-powellite replaces
stage-A grains along fractures and rims. Crystals of paraniite-(Y) occur as small inclusions (~1 micron) in
stage-B scheelite-powellite.
At Fianel, paraniite-(Y) is characterised by elevated Mo, and seems to have crystallised under the influence
of W- and LREE-rich fluids during stage B
(AM 83.9.1100-1110).
Paraniite-(Y) from Fianel - Image
Back to Minerals