Distinguishing among schoepite, [(UO{sub 2}){sub 8}O{sub 2}(OH){sub 12}](H{sub 2}O){sub 12}, and related minerals by X-ray powder diffraction
- Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, R3T 2N2 (Canada)
- Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico, 87131 (United States)
We have calculated X-ray powder-diffraction data for schoepite, [(UO{sub 2}){sub 8}O{sub 2}(OH){sub 12}](H{sub 2}O){sub 12}, using unit-cell and atomic parameters from the crystal structure ({bold {ital a}} 14.337, {bold {ital b}} 16.813, {bold {ital c}} 14.781, Z=4, D{sub x}=4.87gcm{sup {minus}3}). Schoepite crystallizes in space group P2{sub 1}ca but is strongly pseudo- centrosymmetric, and observed reflections (I{sub rel}{gt}0.1{percent}) conform to space group Pbca. The six strongest reflections for schoepite are [d({Angstrom}), hkl (relative intensity)] 7.365, {ital 002} (100), 3.253, {ital 242} (55), 3.626, {ital 240} (36), 3.223, {ital 402} (25), 3.683, {ital 004} (20), 2.584, {ital 244} (18). The calculated intensities of reflections that distinguish space group Pbca from space group Pbna (the space group of metaschoepite), i.e., h0l with h odd and l even, are weak, and may not be evident in experimental powder patterns. The {bold {ital a}} axis of schoepite (14.34 {Angstrom}) is significantly longer than that of synthetic metaschoepite (13.98 {Angstrom}), and the two phases can best be distinguished by their unit-cell parameters. However, potential overlap of the strongest reflections can make identification and unit-cell determination difficult, especially for fine-grained material. Natural samples commonly contain intergrowths of schoepite, metaschoepite, and dehydrated schoepite. The calculated powder pattern for schoepite agrees well with data reported for natural schoepite (PDF 13-241) but shows discrepancies with the data from synthesis products. Data for {open_quotes}synthetic schoepite{close_quotes} indicate that this product was a mixture. Powder data labeled {open_quotes}paraschoepite{close_quotes} in the Powder Diffraction File do not correspond to the mineral of that name. {copyright} {ital 1997 International Center for Diffraction Data.}
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG03-95ER14540
- OSTI ID:
- 550495
- Journal Information:
- Powder Diffraction, Journal Name: Powder Diffraction Journal Issue: 4 Vol. 12; ISSN 0885-7156; ISSN PODIE2
- Country of Publication:
- United States
- Language:
- English
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