FERRO-FERRI-NYBØITE, NaNa2(Fe2+3Fe3+2)(Si7Al)O22(OH)2, A NEW CLINOAMPHIBOLE FROM MONT SAINT-HILAIRE, QUÉBEC, CANADA: DESCRIPTION AND CRYSTAL STRUCTURE

Abstract

Abstract Ferro-ferri-nyboite, NaNa 2 (Fe 2+ 3 Fe 3+ 2 )(Si 7 Al)O 22 (OH) 2 , is a new mineral of the amphibole group from Poudrette quarry, Mont Saint-Hilaire, La Vallee-du-Richelieu RCM, Monteregie (formerly Rouville County), Quebec, Canada. It occurs in an igneous microbreccia associated with a eudialyte-group mineral, an astrophyllite-group mineral, albite, and nepheline. Crystals are prismatic parallel to [001] with {100} and {110} forms and cleavage surfaces, and the prism direction is terminated by irregular fractures. Grains are up to 3 cm long, and occur as blocky aggregates. Crystals are black with a greyish-green to black streak. Ferro-ferri-nyboite is brittle, has a Mohs hardness of 6 and a splintery fracture; it is non-fluorescent with perfect {110} cleavage, no observable parting, and has a calculated density of 3.424 g/cm 3 . Crystals show extreme optical absorption due to intervalence charge transfer, which inhibited measurement of optical properties. Ferro-ferri-nyboite is monoclinic, space group C 2/ m , a 9.9190(5), b 18.0885(8), c 5.3440(3) A, β 103.813(1)°, V 931.09(13) A 3 , Z = 2. The strongest ten X-ray diffraction lines in the powder pattern are [ d in A( I )( hkl )]: 8.520(100)(110), 3.162(55)(310), 2.834(24)(330), 1.671(19)(461), 2.732(10)(151), 2.552(10)( 2 ¯ 02), 2.344(9)( 3 ¯ 51), 3.298(7)(240), 2.606(6)(061), 1.446(6)( 6 ¯ 61,4.10.0). Analysis by a combination of electron microprobe and Mossbauer spectroscopy gives SiO 2 45.80, Al 2 O 3 3.11, TiO 2 0.50, Fe 2 O 3 11.18, FeO 23.45, MnO 2.28, ZnO 0.12, MgO 0.23, CaO 0.99, Na 2 O 8.01, K 2 O 1.30, F 0.81, H 2 O calc 1.47, O ≡ F−0.34 sum 98.91 wt.%. The formula unit, calculated on the basis of 24 (O + OH + F) with (OH + F) = 2 apfu is (Na 0.66 K 0.27 ) Σ0.93 (Na 1.83 Ca 0.17 ) Σ2.00 (Mg 0.06 Fe 2+ 3.15 Mn 0.31 Zn 0.01 Fe 3+ 1.38 Ti 0.06 Al 0.03 ) Σ5.00 (Si 7.35 Al 0.65 ) Σ8.00 O 22 (OH 1.58 F 0.42 ) Σ2.00 . Ferro-ferri-nyboite, ideally NaNa 2 (Fe 2+ 3 Fe 3+ 2 )(Si 7 Al)O 22 (OH) 2 , is related to endmember nyboite, NaNa 2 (Mg 3 Al 2 )(Si 7 Al)O 22 (OH) 2 by the substitutions Fe 2+ → Mg and Fe 3+ → Al.