HOGTUVAITE, A NEW BERYLLIAN MEMBER OF THE AENIGMATITE GROUP FROM NORWAY, WITH NEW X-RAY DATA ON AENIGMATITE

Hogtuvaite, essentially (Ca, Na)2 (Fe2+, Fe3+, Ti, Mg, Mn, Sn)6 (Si, B e, Al)6 O20, is a new beryllian member of the aenigmatite group that w as discovered in Nordland County, Norway. It is a metamorphic mineral, hosted by Proterozoic granitic gneisses and mafic pegmatites of metam orphic origin. Compositional variations within and between gneiss-host ed samples of hogtuvaite are minimal; however, pegmatite-hosted sample s of hogtuvaite are significantly different, containing less Al and Sn , and more Ti and Mn, than those from the gneisses. The composition of type hogtuvaite (in wt.%) is CaO 10.44, Na2O 1.52, FeO 28.06, Fe2O3 1 9.03, TiO2 2.77, MgO 0.42, MnO 0.27, SnO2 0.53, SiO2 31.60, BeO 2.65, Al2O3 2.64. Hogtuvaite forms black, elongate, poikiloblastic crystals. It has a dark green streak, an uneven fracture, two good cleavage dir ections, and a nonmetallic subadamantine luster. It is nonmagnetic, is not fluorescent, and does not react to most common acids and bases. H owever, it does dissolve slowly in cold hydrofluoric acid. Its measure d density is 3.85 g/cm3, and the calculated density is 3.98 g/cm3. The mineral is opaque to subtransparent, biaxial negative (?) with a larg e 2V, strongly pleochroic (bronze to green) and has alpha' 1.78 and ga mma' 1.82. It is triclinic (pseudo-monoclinic), space group P1BAR, wit h a 10.317(1), b 10.724(1) c 8.855(1) angstrom, alpha 105.77(1)degrees , beta 96.21(1)degrees, gamma 124.77(1)degrees, V 730.4(1) angstrom3, and Z = 2. All samples are intensely polysynthetically twinned. The st rongest seven X-ray powder-diffraction lines [d in angstrom(1)(hkl)] a re 2.5293(100)(420BAR), 8.048(90)(010), 2.0979(63)(251BAR), 2.9247(59) (031BAR), 2.6761(48)(241BAR), 2.0747(47)(411BAR) and 3.125(46)(021). A new and uniquely indexed set of X-ray powder diffraction data for aen igmatite is presented. The name hogtuvaite is inspired by the highest peak near die type locality.