New data on lacroixite, NaAlFPO4

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Authors:Pajunen, Aarne; Lahti, Seppo I.
Author Affiliations:Primary:
Univ. Helsinki, Dep. Inorg. Chem., Helsinki, Finland
Other:
Geol. Surv. Finl., Finland
Volume Title:American Mineralogist
Source:American Mineralogist, 70(7-8), p.849-855. Publisher: Mineralogical Society of America, Washington, DC, United States. ISSN: 0003-004X
Publication Date:1985
Note:In English; illus. incl. 5 tables
Summary:Museum specimens of lacroixite from the type locality (near Freifenstein, East Germany) were restudied. The mineral occurs in druses of a Li-bearing granite in close association with viitaniemiite, the physical properties of which have been cited for lacroixite in the literature. Lacroixite (NaAlFPO4, C/2c, a 6.414, b 8.207, c 6.885 A, beta 115.47°, Z = 4) has strongest XRD peaks 3.155(100), 2.895(98), 2.476(57), 4.73(51), 2.166(43), 4.627(32) A. The specific gravity is 3.29 and H. 4-5. The mineral is colourless or grey, biaxial with alpha 1.546, beta 1.563, gamma 1.580, 2Valpha (calc) 89.1°; r < v. The structure of lacroixite has been solved by Patterson and Fourier methods. After the least-squares refinement the final R is 0.034 for 468 (2sigma observed) reflections collected on a sharing AlO4F2 octahedra cross-linked by PO4 tetrahedra. The resulting large cavities in the framework are filled with Na atoms in 7-fold coordination. Lacroixite is the phosphate analogue of durangite, NaAlFAsO4; both are isostructural with high-T (A2/a) titanite, CaTiOSiO4. [J.A.Z.]
Subjects:Crystal chemistry; Crystal structure; Mineralogy; Minerals; Nesosilicates; Orthosilicates; Phosphates; Properties; Silicates; Titanite; Titanite group; X-ray data; Central Europe; Europe; Germany; Saxony Germany; Durangite; East Germany; Greifenstein; Lacroixite; NaAlFPO<4`
Abstract Numbers:86M/2242
Record ID:1986019547
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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