Publication Type:

Journal Article

Authors:

Haring, M. M. M.; McDonald, A. M.

Source:

Mineralogical Magazine, Mineralogical Society, London, United Kingdom, Volume 78, Number 3, p.591-607 (2014)

ISBN:

0026-461X

Keywords:

bonding, Canada, cell dimensions, crystal chemistry, crystal structure, eastern canada, feldspathoid rocks, formula, FTIR spectra, hydrogen, hydroxides, igneous rocks, infrared spectra, Mont-Saint-Hilaire Quebec, Monteregian Hills, niobates, octahedra, oxides, polyhedra, quebec, Raman spectra, refinement, Rouville County Quebec, single-crystal method, space groups, spectra, x-ray diffraction data

Abstract:

The crystal structure of franconite, NaNb (sub 2) O (sub 5) (OH).3H (sub 2) O, has been characterized by single-crystal X-ray diffraction using material from Mont Saint-Hilaire, Quebec, Canada. Results give a = 10.119(2), b = 6.436(1), c = 12.682(2) Aa and beta = 99.91(3) degrees and confirm the correct space group as P2 (sub 1) /c. The crystal structure, refined to R = 4.63% and wR (super 2) =11.95%, contains one Na site, two distorted octahedral Nb sites and nine O sites. It consists of clusters of four edge-sharing Nb(O,OH) (sub 6) octahedra, linked through shared corners to adjacent clusters, forming layers of Nb(O,OH) (sub 6) octahedra. These alternate along [100] with layers composed of NaO(H (sub 2) O) (sub 4) polyhedra, the two being linked together by well defined H bonding. The predominance of H bonding, essential to the mineral, results in a perfect {100} cleavage. Chemical analyses (n = 7) of four crystals give the empirical formula (Na (sub 0.73) Ca (sub 0.13) [] (sub 0.14) ) (sub Sigma =1.00) (Nb (sub 1.96) Ti (sub 0 .02) Si (sub 0.02) Al (sub 0.01) ) (sub Sigma =2.01) O (sub 5) (OH).3H (sub 2) O (based on nine oxygens) or ideally NaNb (sub 2) O (sub 5) (OH).3H (sub 2) O. Franconite is crystallo-chemically related to SOMS [Sandia Octahedral Molecular Sieves; Na (sub 2) Nb (sub 2-x) M (sub x) O (sub 6-x) (OH) (sub x) .H (sub 2) O with M = Ti, Zr, Hf], a group of synthetic compounds with strong ion-exchange capabilities. Both hochelagaite (CaNb (sub 4) O (sub 11) .nH (sub 2) O) and ternovite (MgNb (sub 4) O (sub 11) .nH (sub 2) O) have X-ray powder diffraction patterns and cation ratios similar to those of franconite indicating that these minerals probably have similar structures.

Notes:

GeoRef, Copyright 2018, American Geological Institute.<br/>2014-096926<br/>franconite<br/>hochelagaite<br/>Poudrette Quarry<br/>sodalite syenite<br/>ternovite