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Polyakovite-(Ce): (Ce,La,Nd,Pr,Ca)4(Mg,Fe++)(Cr,Fe+++)2(Ti,Nb)2Si4O22
Comments: Black, pitchy, polyakovite-(Ce) crystal showing conchoidal surfaces so typical for this mineral. Green fluororichterite overgrowth is just visible. Measured radioactivity is 146µR/h. Location: Pit No. 97 (N97 Mine), Ilmen Natural Reserve, Ilmen Mts, Chelyabinsk Oblast', Southern Urals, Urals Region, Russia. Scale: Specimen size is 4.5x3x2.5 cm. © Pavel M. Kartashov