Gagarinite-(Ce)
Gagarinite-(Ce) previously zajacite-(Ce) is a rare radioactive fluoride mineral with formula Na(REExCa1−x)(REEyCa1−y)F6. REE refers to rare-earth elements, mostly those belonging to the lanthanide series. It crystallizes in the trigonal rhombohedral system and has a white vitreous appearance with a conchoidal fracture. It has a Mohs hardness of 3.5 and a specific gravity of 4.44 to 4.55. Zajacite is transparent with refractive indices nω = 1.483 and nε = 1.503. Gagarinite-(Y) is a yttrium-rich analog.
Intro adapted from Wikipedia (CC BY-SA).
Gagarinite-(Ce) is an IMA-recognized mineral species in the halide class, with the chemical formula NaCaCeF₆.
It crystallizes in the hexagonal crystal system (space group P6_3/m). It is a member of the Gagarinite structural group.
Key properties: Mohs hardness 3.5; specific gravity 4.44; White streak; Vitreous luster; optically uniaxial.
IMA symbol Gag-Ce, IMA status: approved, named in 1993.
Found in a rare-earth-element enriched, peralkaline granitic complex (Strange Lake).
It is found associated with Vlasovite, narsarsukite, willemite, fluorite (Strange lake).
The mineral was named to honor the first cosmonaut, Yuri Alekseevich Gagarin (1934-1968) and a suffix for the dominant rare earth element, cerium.