Crystal chemistry of REEXO4 compounds (X = P,As, V). I. Paragenesis and crystal structure of phosphatian gasparite-(Ce) from the Kesebol Mn-Fe-Cu deposit, Vastra Gotaland, Sweden

Abstract

A new occurrence of the rare arsenate species gasparite-(Ce), ideally CeAsO 4 , is reported from the Kesebol Mn-Fe-Cu deposit in south-western Sweden, where it occurs as yellowish euhedral crystals up to 0.5 mm in maximum size, in association with rhodonite, andradite, Mn 2+ -dominant “allanite-(Ce)”, chernovite-(Y), manganoan calcite and quartz. All gasparite samples studied are phosphatian, and quantitative SEM-EDS analyses of two representative grains gave the following average compositions: Ce 0.77 La 0.10 Nd 0.10 Pr 0.02 Ca 0.01 Th 0.007 [As 0.84 P 0.12 Si 0.03 ]O 4 and Ce 0.79 La 0.11 Nd 0.11 Th 0.010 [As 0.85 P 0.11 Si 0.02 ]O 4 . The Kesebol gasparite-(Ce) is distinguished from the type material by a higher Ce/REE tot ratio and a significant P content. The crystal structure of phosphatian gasparite-(Ce) has been determined from single-crystal X-ray diffractometer data (Mo Ka radiation, CCD area detector) and refined in space group P2 1/n to R(F) = 2.86 % for 776 ‘observed’ reflections with F o > 4σ( F o ) ( a = 6.929(3), b = 7.129(3), c = 6.697(3) A, β = 104.46(3)°, V = 320.3(2) A 3 , Z = 4). The results confirm that gasparite-(Ce) has a monazite-type structure, and give the idealised formula (Ce, La, Nd)[(As 0.71 P 0.29 )O 4 ].