Original paper

Atelisite-(Y), a new rare earth defect silicate of the KDP structure type

Malcherek, Thomas; Mihailova, Boriana; Schlüter, Jochen; Husdal, Tomas

Abstract

The title mineral has been discovered in a granitic pegmatite at the Stetind quarry, Tysfjord, Norway. Atelisite-(Y) forms pale brown to colourless, transparent crystals of dipyramidally terminated, short-prismatic habit with a diameter of up to 0.3 mm. Based on electron microprobe analysis and 16 anions per formula unit, the empirical formula is (Y3.11 Yb0.46Er0.19Dy0.11Gd0.09Ho0.01Tb0.02)Σ3.99Si2.40O16H10.43. The presence of hydroxyl-groups is inferred from the detection of OH-stretching modes near 3225 cm1 in Raman spectra of the new mineral. The crystal structure of atelisite was solved and refined on single-crystal X-ray diffraction data in space group I42d, with a = 6.947(4), c = 6.133(3) Å, V = 295.98(28) Å3. Site occupancy refinement at the 4a-site approaches 3/4 Si-occupancy, if the 4b-site is fully occupied by Y and Yb, with a refined Y/Yb ratio of 4. This suggests an idealized formula of Y4Si3O8(OH)8 for atelisite-(Y). The crystal structure of the new mineral is of particular interest with regard to the known occurrence of hydrous species in the nominally anhydrous minerals xenotime and zircon.

Keywords

rare earth elementszirconxenotime mineralatelisite-(y)new mineralcrystal structureyttrium silicate hydratetetrahedral vacancykdp structure typestetint (tysfjord, norway)