Paraniite-(Y)

paraniite-(Y)

scheelite

powellite

monazite-(Ce)

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

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