HYDROXYLGUGIAITE: A NEW BERYLLIUM SILICATE MINERAL FROM THE LARVIK PLUTONIC COMPLEX, SOUTHERN NORWAY AND THE ILIMAUSSAQ ALKALINE COMPLEX, SOUTH GREENLAND; THE FIRST MEMBER OF THE MELILITE GROUP TO INCORPORATE A HYDROGEN ATOM

Hydroxylgugiaite, ideally (Ca-3 square(1))Sigma(4)(Si3.5Be2.5)Sigma O-6(11)(OH)(3), is a new mineral species from two localities in the Larvik plutonic complex in Porsgrunn, Telemark, Norway, and one locality in Ilimaussaq, Greenland. Hydroxylgugiaite crystals occur as squat dipyramids {111} (30 3 50 mu m) or as elongate tetragonal prisms. The crystals are translucent, white to pale grey in color, with a white streak and vitreous luster. It is brittle, with no apparent cleavage. Hydroxylgugiaite is uniaxial positive with omega= 1.622 +/- 0.002 and epsilon=1.632 +/- 0.002. There is no pleochroism and birefringence is low. The average of eight analyses of a single grain of type material (oxide wt.%) gave Na2O 2.04, CaO 32.90, FeO 0.22, MnO 0.74, BeO 13.47 (LA-ICP-MS), Al2O3 0.74, SiO2 44.06, F 1.74, H2O (assuming 3 OH+ F) 4.93, Total (-0.73 O = F) 100.10. Potassium, strontium, and magnesium were measured but not detected. The calculated density is 2.79 g cm(-3). The empirical formula on the basis of 14 anions including 3 OH-+F- is: (Ca2.76Na0.31Mn0 Fe-.05(0.01))(Sigma 3.13)(Si3.45Be2.53Al0.07) O-Sigma 6.05(11)[(OH) F-2.57(0.43)]Sigma 3. The formula from crystal-structure analysis of the Saga specimen is: (Ca-3.02 square(0.98))(Sigma 4)(Si1.79Be0.21)(Sigma 2)(Be2.29Si1.71)(Sigma 4)O-11(OH)(3). Combined structural and chemical data gives the following formula for the Nakkaalaaq specimen: (Ca-2.88 square 0.98Na0.12Mn0.02)(Sigma 4)(Si 1.80Be0.17Al0.03)(Sigma 2) (Be2.32Si1.68)(Sigma 4)O-11[(OH) F-2.70(0.30)] Sigma(3); with simplified formula (Ca,square) (4)(Si, Be) (2)(Be, Si) O-4(11)(OH) (3). The crystal structure of hydroxylgugiaite is tetragonal in acentric space group P421/m, with a 7.4151(2), b 7.4151, c 4.9652(1)angstrom, V 272.9(1) angstrom(3), and Z = 1. It has been refined to an R index of 0.028 on the basis of 342 observed reflections and a correction for the {110} twin law. It is an H-bearing member of the melilite group. The structure has two distinct layers. The one crystallographically distinct Ca site with eight-fold coordination is a square antiprism polyhedron. The Ca polyhedra are in a layer with the H atoms. A second layer consists of corner-sharing Si/Be atoms in tetrahedral coordination with O. One H atom is bonded to an apical O atom that is not shared by two tetrahedra. This H atom is present only when there is a Ca-site vacancy. The other H atom is loosely bonded to the same O atom but at a different site. The IR spectrum supports this H-bonding scheme. Additional hydroxylgugiaite data is given for the other localities.