ALBERT

Description: Mn-bearing hellandite-(Y) occurs as pinkish yellow granular crystals (up to sub mm) in the Sc-rich granite pegmatite at Heftetjern, Tørdal, Telemark, Norway. Associated minerals are quartz, albite, Sc- and Ce-bearing epidote, hingganite-(Y), and an undetermined Ca-bearing hingganite-related mineral. Electron microprobe analyses give an empirical formula as Ca 1.34 Mn 1.07 Y 2.75 Ce 0.02 Nd 0.02 Sm 0.01 Gd 0.01 Dy 0.05 Er 0.05 Yb 0.15 Al 0.94 Fe 0.08 Si 3.99 B 4.33 O 22.00 (OH) 2.00 on the basis of Al+Fe+Si = 5 and 24 anions per formula unit. The lattice parameters were refined from diffraction data obtained using a Gandolfi camera with an imaging plate and Ni filtered Cu K α; a 18.693(17), b 4.651(3), c 10.178(7) Å, β = 111.37(6)°, V 824.1(10) Å 3 . The crystal structure was refined from single-crystal XRD data obtained with a CCD-diffractometer and graphite-monochromated Mo K α. The refinement with anisotropic atomic displacement parameters converged to R 1 = 0.0269 for 1567 reflections [ I 〉 2( I )] and 0.0318 for all 1768 reflections, resulting in the structural formula M 3 (Ca 0.56 Mn 0.44 ) 2 M 4 (Y 0.43 Ca 0.23 Ln 0.14 0.20 ) 2 M 2 (Y 0.94 Ln 0.06 ) 2 M 1 (Al 0.92 Fe 0.08 )Si 4 B 4 O 21.21 (OH) 2.79 . In this hellandite-(Y), Mn 2+ replaces Ca 2+ at the M 3 site and there is a significant vacancy at the M 4 site. The T site is vacant, and, instead, the O5 position is occupied by (OH) – .