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Formula: (Ca3REE)Na3Nb(Si2O7)2(OF)F2
Sorosilicate (Si2O7 groups), rinkite group,
seidozerite supergroup,
rare earth- and niobium-
bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.45 measured, 3.43 calculated for the empirical formula
Hardness: 5
Colour: Colourless
Luminescence: No fluorescence under UV
Environments
Nacareniobsite-(Ce) occurs in alkaline undersaturated igneous rocks and oversaturated peralkaline
granites
(HOM).
Localities
The Papanduva pluton, Morro Redondo complex, Tijucas do Sul, Paraná, Brazil, consists of a variety of peralkaline
alkali feldspar
granites.
The nacareniobsite-(Ce)- and britholite-(Ce)- bearing
samples consist of deformed and oriented, ellipsoidal to irregular
alkali feldspar,
arfvedsonite and rare quartz
megacrystals (up to 4.0 mm in size) in a fine-grained saccharoidal matrix with
quartz, microcline,
albite, fluorite,
aegirine, some
arfvedsonite, and combinations of several rare accessory minerals,
including narsarsukite,
rare earth element-rich
turkestanite, elpidite, and
other (Na,K)-zirconosilicates
(CM 51.2.313-332).
At the type locality, the Kvanefjeld adit, Kvanefjeld deposit, Kuannersuit Plateau (Kvanefjeld), Ilímaussaq
complex, Kujalleq, Greenland, the nacareniobsite-(Ce) forms individual ruler-shaped crystals up to
3.0 x 0.04 x 0.04 mm3, and tabular crystal aggregates that are colourless and transparent with a vitreous
lustre.
Nacareniobsite occurs in dissolution cavities and in the matrix
lujavrite
(AM 75.708).
Associated minerals include arfvedsonite,
sodalite, eudialyte,
villiaumite, microcline
and albite
(HOM).
Nacareniobsite-(Ce) from the Kanefjeld Adit -
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