Natropalermoite, Na2SrAl4(PO4)(4)(OH)(4), a new mineral isostructural with palermoite, from the Palermo No. 1 mine, Groton, New Hampshire, USA

Natropalermoite, ideally Na2SrAl4(PO4)(4)(OH)(4), the Na-analogue of palermoite, is a new mineral from the Palermo No. 1 mine, Groton, New Hampshire, USA. Associated minerals are palermoite, eosphorite and quartz. Natropalermoite crystals are prismatic with striations parallel to the direction of elongation (the a axis) up to 200 mu m x 50 mu m x 45 mu m in size. The mineral is colourless, transparent with a white streak and vitreous lustre and is visually indistinguishable from palermoite. It is brittle with subconchoidal fracture and has a Mohs hardness of 5.5. Cleavage is perfect on {001}, fair on {100} and no parting was observed. The calculated density is 3.502 g cm(-3). Natropalermoite is biaxial (-), alpha = 1.624(1), ss = 1.641(1), gamma = 1.643(1) (589 nm), 2V(meas) = 43(4)degrees, 2V(calc) = 38 degrees. An electronmicroprobe analysis yielded an empirical formula (based on 20 O apfu) of (Na1.69Li0.31)(Sigma 2.00) (Sr0.95Mg0.04C a(0.02)Ba(0.01))(Sigma 1.02) (Al3.82Mn0.03Fe0.03)(Sigma 3.88) (P1.01O4)(4)(OH)(4). Natropalermoite is orthorhombic, space group Imcb, a = 11.4849(6), b = 16.2490(7), c = 7.2927(4) angstrom, V = 1360.95(17) A(3), Z = 4. Natropalermoite is isotypic with palermoite, but substitution of the larger Na for Li results in substantial increase of the b cell parameter. Four of the seven Na-O distances are longer than their equivalents in palermoite, resulting in a more regular 7-fold coordination polyhedron about Na. The eight strongest peaks in the calculated X-ray powder diffraction are [d(calc) (angstrom), I-rel%, (hkl)]: [3.128, 100, (321)], [4.907, 68, (121)], [3.327, 48, (022)], [4.689, 45, (220)], [3.078, 45, (202)], [2.453, 38, (242)], [2.636, 35, (411)], [2.174, 35, (422)].12 month embargo; published online: 01 August 2018.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu