|Unit cell||a = 6.099 Å, c = 11.064 Å, Z = 3|
|Color||Colorless, pale pink, orange|
|Crystal symmetry||Trigonal - rhombohedral
H-M symbol: (3)
Space group: P3
|Mohs scale hardness||3.5|
|Specific gravity||4.44 - 4.55|
|Optical properties||Uniaxial (+)|
|Refractive index||nω = 1.483 nε = 1.503|
|Birefringence||δ = 0.020|
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 of nω=1.483 and nε=1.503. Gagarinite-(Y) is a yttrium rich analog.
It was discovered in 1993 at Strange Lake, Quebec - Labrador, (56°20'N, 64°10'W) and was initially named for Ihor Stephan Zajac, who led the expedition responsible for its discovery, and who first recognized the presence of the new mineral. The mineral was renamed gagarinite-(Ce) in 2010 by the IMA. The new name is for Russian cosmonaut Yuri Gagarin (1934–1968).
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