Nepheline: Structure of Three Samples from the Bancroft Area, Ontario, Obtained using Synchrotron High-Resolution Powder X-Ray Diffraction

Journal Article · Tue May 25 04:00:00 EDT 2010 · Can. Mineral.

DOI:https://doi.org/10.3749/canmin.48.1.69· OSTI ID:1002404

Antao, Sytle M; Hassan, Ishmael ^[1]

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1. Calgary

The crystal structure of three samples of nepheline (ideally, K{sub 2}Na{sub 6}[Al{sub 8}Si{sub 8}O{sub 32}]) from the Bancroft area of Ontario (1a, b: Egan Chute, 2: Nephton, and 3: Davis Hill), each with different types of superstructure reflections, has been studied using synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinement. The samples have different origins. The structure was refined in space group P6{sub 3}. The R{sub F}{sup 2} index, number of unique observed reflections, pseudohexagonal subcell parameters, and site-occupancy factor (sof) for the K site are as follows: Sample 1b: R{sub F}{sup 2} = 0.0433, N{sub obs} = 1399, a = 9.99567(1), c = 8.37777(1) {angstrom}, V = 724.907(2) {angstrom}{sub 3}, and K (sof) = 0.716(1). Sample 2: R{sub F}{sup 2} = 0.0669, N{sub obs} = 1589, a = 10.00215(1), c = 8.38742(1) {angstrom}, V = 726.684(1) {angstrom}{sub 3}, and K (sof) = 0.920(1). Sample 3: R{sub F}{sup 2} = 0.0804, N{sub obs} = 1615, a = 9.99567(1), c = 8.37873(1) {angstrom}, V = 724.991(1) {angstrom}{sub 3}, and K (sof) = 0.778(2). Sample 2 has the largest sof for K and the largest volume. The satellite reflections in the three nepheline samples were observed in the HRPXRD traces and give rise to different incommensurate superstructures. The Al and Si atoms in the T{sub 3} and T{sub 4} sites are ordered differently in the three samples, which may indicate the presence of a domain structure based on Al-Si order. The positions for the Al and Si atoms were interchanged in two samples because of the resulting <T-O> distances. The slight excess of Si over Al atoms, characteristically encountered in well-analyzed samples of nepheline, is reflected in the <T-O> distances.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: USDOE
• OSTI ID: 1002404
• Journal Information: Can. Mineral., Journal Name: Can. Mineral. Journal Issue: (1) ; 02, 2010 Vol. 48; ISSN CAMIA6; ISSN 0008-4476
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

58 GEOSCIENCES
CRYSTAL STRUCTURE
DATA
DOMAIN STRUCTURE
NEPHELINE BASALTS
ONTARIO
ORDER PARAMETERS
X-RAY DIFFRACTION