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Formula: Cs6(Ce,REE,Ca)30(Si70O175)(OH,F,H2O)35
Unclassified silicate, cesium- and
cerium- bearing mineral
Crystal System: Isometric
Specific gravity: 3.12 measured, 3.07 calculated
Hardness: 5 to 5½
Streak: White
Colour: Colourless to clear tea colour
Environments
Mendeleevite-(Ce) is a relatively new mineral, approved in 2010 and to date (April 2025) reported only
from the type locality.
Localities
At the type locality, the Dara-i-Pioz Massif, Districts of Republican Subordination, Tajikistan,
mendeleevite-(Ce) was found in the moraine of the Darai-Pioz glacier in nest-like segregations of a
polymineral aggregate composed of brownish grey fine to medium granular
pectolite with subordinate amounts of
quartz, aegirine and
fluorite, in a quartz-rich rock
with sogdianite,
stillwellite-(Ce),
reedmergnerite,
leucosphenite, aegirine,
polylithionite, microcline,
pyrochlore and turkestanite.
Other associated minerals are hyalotekite,
sokolovaite, kirchhoffite,
pekovite, neptunite and
zeravshanite.
Mendeleevite-(Ce) forms usually colourless, but sometimes clear tea colour, individual well-formed cubic
crystals with a size of 10 to 30 μm, while relatively large (up to 100 μm) segregations associated with
zeravshanite and light-green
aegirine are rare
(AM 99.871-872).
Mendeleevite-(Ce) from the Dara-i-Pioz Massif -
Image
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