THE CRYSTAL STRUCTURES OF LOPARITE-(Ce)

The structures of three compositionally distinct crystals of loparite-(Ce) have been determined by single-crystal X-ray diffractometry using a CCD area detector. Niobian calcian loparite-(Ce) from the Khibina complex, in Russia, is orthorhombic [Pbnm; a 5.5108(14), b 5.5084(14), c 7.7964(20) Å]. Calcian niobian loparite-(Ce) from the Lovozero complex, also in Russia, is tetragonal [I4/mcm; a 5.5022(11), c 7.7967(16) Å]. Strontian calcian loparite-(Ce) from the Bearpaw Mountains, in Montana, is tetragonal [I4/mcm; a 5.5076(17), c 7.7767(24) Å]. None of these samples show any evidence of cation order at the A or B site. All examples of loparite-(Ce) have the general formula (Na,Ce,Ca)2(Ti,Nb)2O6. These structural and compositional data indicate that loparite requires redefinition as a mineral species.