Atelisite-(Y), a new rare earth defect silicate of the KDP structure type
Malcherek, Thomas; Mihailova, Boriana; Schlüter, Jochen; Husdal, Tomas
European Journal of Mineralogy Volume 24 Number 6 (2012), p. 1053 - 1060
published: Dec 1, 2012
ArtNo. ESP147052406009, Price: 29.00 €
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.