Publication Date:
2017-07-06
Description:
Natropalermoite, ideally Na 2 SrAl 4 (PO 4 ) 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 μm x 50 μm x 45 μm 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 (–), α = 1.624(1), β = 1.641(1), = 1.643(1) (589 nm), 2V meas = 43(4) o , 2V calc = 38 o . An electron microprobe analysis yielded an empirical formula (based on 20 O apfu) of (Na 1.69 Li 0.31 ) 2.00 (Sr 0.95 Mg 0.04 Ca 0.02 Ba 0.01 ) 1.02 (Al 3.82 Mn 0.03 Fe 0.03 ) 3.88 (P 1.01 O 4 ) 4 (OH) 4 . Natropalermoite is orthorhombic, space group Imcb , a = 11.4849(6), b = 16.2490(7), c = 7.2927(4) Å, V = 1360.95(17) Å 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 (Å), 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)].
Print ISSN:
0026-461X
Electronic ISSN:
1471-8022
Topics:
Geosciences
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