Mendeleevite-(Ce)

mendeleevite-(Ce)

pectolite

zeravshanite

stillwellite-(Ce)

Images

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

Pegmatites

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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