Mn-BEARING HELLANDITE-(Y) FROM THE HEFTETJERN PEGMATITE, TØRDAL, NORWAY

Mn-bearing hellandite-(Y) occurs as pinkish yellow granular crystals (up to sub mm) in the Sc-rich granite pegmatite at Heftetjern, Tordal, 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 Ca1.34Mn1.07Y2.75Ce0.02Nd0.02Sm0.01Gd0.01Dy0.05Er0.05Yb0.15Al0.94Fe0.08Si3.99B4.33O22.00(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) A, β = 111.37(6)°, V 824.1(10) A3. 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 > 2σ( I )] and 0.0318 for all 1768 reflections, resulting in the structural formula M 3(Ca0.56Mn0.44)2 M 4(Y0.43Ca0.23Ln0.14□ 0.20)2 M 2(Y0.94Ln0.06)2 M 1(Al0.92Fe0.08)Si4B4O21.21(OH)2.79. In this hellandite-(Y), Mn2+ replaces Ca2+ 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)–.