Cesiokenopyrochlore

cesiokenopyrochlore

behierite

rynersonite

xenotime-(Y)

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Formula: ☐Nb2(O,OH)6Cs1-x
Oxide, niobium- and cesium- bearing mineral
Specific gravity: 5.984 calculated
Hardness: 5
Colour: Light brown
Luminescence: Non-fluorescent in UV
Environments

Pegmatites

Cesiokenopyrochlore is a rare mineral; it was approved in 2016 and to date (July 2022) has been reported only from the type locality.

Localities

At the type locality, the Tetezantsio pegmatites, Tetezantsio-Andoabatokely Pegmatite Field, Andrembesoa, Betafo, Vakinankaratra, Madagascar, cesiokenopyrochlore was discovered in a sample from a rare-element granitic pegmatite.
Central Madagascar is characterised by a tectonic structure with a lower unit of gneiss and an upper unit of quartzites, schists, and marbles. Both units are locally intruded by granitic pegmatites, which probably formed via fractional crystallisation of granitic plutons emplaced at relatively shallow depths. The pegmatites consist of grey K-feldspar, white to smoky quartz, white albite, multicoloured tourmaline, colourless to pink or green spodumene, and a variety of accessory minerals.
The cesiokenopyrochlore-bearing sample represents a well formed tetrahedral bipyramidal greyish brown béhierite crystal 7 mm across in a cavity of quartz-orthoclase aggregate. Associated minerals include elbaite as pink transparent crystals up to 1 mm, rynersonite as darkred crystals up to 0.1 mm, muscovite, xenotime-(Y), pollucite, zircon, and a clay mineral, presumably kaolinite, in a cavity.
Cesiokenopyrochlore is a late-stage mineral forming rough equant crystals up to 0.05 mm overgrowing béhierite and rynersonite, which occurs on the surface of the béhierite crystal (CM 59.1.149–157).

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