Alflarsenite, a new beryllium-silicate zeolite from a syenitic pegmatite in the Larvik plutonic complex, Oslo region, Norway

Alflarsenite is a new beryllium-silicate zeolite with chemical composition close to NaCa (sub 2) Be (sub 3) Si (sub 4) O (sub 13) (OH).2H (sub 2) O. It is a late-stage hydrothermal mineral from a syenitic pegmatite in the Tuften larvikite quarry, Tvedalen, Larvik, Vestfold, south Norway. Closely associated minerals are calcite, analcime and K-feldspar. Alflarsenite is monoclinic, P2 (sub 1) , with a=7.1222(4), b=19.8378(11), c= .8071(5) Aa, beta =111.287(1) degrees , V=1291.1(2) Aa (super 3) , Z=4. The crystal structure was refined from single-crystal X-ray data to R1 = 0.045 for 3283 observed reflections. The zeolite structure is novel, consisting of intersecting channels: 5- and 8-membered channel rings along [010] and 3-, 6- and 8-membered channel rings along [100]. The strongest eight reflections of the X-ray powder-diffraction pattern [d(obs.) in Aa (I) (hkl)] are: 9.095 (100) (001), 6.279 (42) (-111, 110), 4.189 (32) (-122, 121), 3.972 (76) (-141, 140), 3.205 (37) (-113, 112), 2.964 (70) (-232, 230), 2.915 (92) (-133, 132), 2.757 (33) (-242, 240). Alflarsenite crystals are colourless (in aggregates pale beige) and bladed; they are flattened on (010) and elongate on [100]. Identified crystal forms are {010}, {0-10}, {001} and {20-1}. Cleavage was not observed. The mineral is biaxial (+) with refractive indices alpha 1.578(1), beta 1.580(1), gamma 1.583(1), measured at 590 nm. 2V (meas.)=82(5) degrees from extinction curves and =76(5) degrees by the Kamb method; 2V (calc.) = 79 degrees . The optical orientation is Z=b, X (circumflex) a = 45(2) degrees . The Mohs hardness is approximately 4; D (calc.)=2.605 g/cm (super 3) .