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Mn-rich fluorapatite from Austria: Crystal structure, chemical analysis, and spectroscopic investigations

Hughes, John M. and Ertl, Andreas and Bernhardt, Heinz-Jürgen and Rossman, George R. and Rakovan, John (2004) Mn-rich fluorapatite from Austria: Crystal structure, chemical analysis, and spectroscopic investigations. American Mineralogist, 89 (4). pp. 629-632. ISSN 0003-004X.

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The crystal structure of a pale blue transparent Mn-rich fluorapatite (MnO: 9.79 wt%) with the optimized formula ~(Ca_(8.56)Mn^(2+)_(1.41)Fe^(2+)_(0.01))P_6O_24F_(2.00) and space group P6_3/m,ɑ = 9.3429(3), c = 6.8110(2) Å, Z = 2 has been refined to R = 2.05% for 609 unique reflections (MoKα). The Mn in the Eibenstein an der Thaya, Austria apatite is strongly ordered at the Ca1 site: Ca1: Ca_(0.72(1))Mn_(0.28), Ca2: Ca_(0.96(1))Mn_(0.04). There is a linear variation in <Ca1-O> as a function of Mn content (r^2 = 1.00). The dominant band in the optical absorption spectrum of fluorapatite from Eibenstein is in the 640 nm region with E || c > E ⊥ c. The 640 nm band is attributed to Mn^(5+) at the P site by analogy with previous studies. This interpretation is consistent with studies of well-characterized synthetic materials of the apatite structure that contain Mn^(5+). Because Mn^(5+) has intense absorption in the visible region of the spectrum, if a small proportion of the total Mn is Mn^(5+) at the P site, that substituent dominates the spectrum and the color of the mineral. To determine if the pale blue color is due to radiation effects, a fragment of the fluorapatite crystal was heated at 400° C for 1 hour, and the change in color was slight. All of these observations are consistent with the origin of color from Mn^(5+). Assuming that all the intensity of the 640 nm (E || c) absorption is from Mn^(5+), the concentration of Mn^(5+) in this fluorapatite sample was calculated as 2.6% of the total manganese content (~P_(5.96)Mn^(5+)_(0.04)). The calibration was estimated from the spectrum of the related compound Sr_5(P_(0.99)Mn^(5+)_(0.01))_3Cl. The weak band at about 404 nm in the E || c spectrum may be the corresponding band for Mn^(2+) in octahedral coordination.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 2004 American Mineralogist. Received May 14, 2003; Accepted October 26, 2003; Manuscript handled by John Hanchar. We thank A. Prayer, Irnfritz, Lower Austria, for providing the apatite samples and A. Wagner, Vienna, Austria, for preparing them. This work was supported in part by NSF grants EAR-9627222 and EAR-9804768 to J.M.H., EAR-0003201 to J.M.H. and J.R., and EAR-0125767 to GRR. Thorough reviews were provided by Associate Editor J.M. Hanchar, P. Piccoli, and M. Gaft. F.C. Hawthorne provided a remarkably detailed review that considerably improved the presentation. The Instrumentation Laboratory of Miami University is gratefully acknowledged for maintaining the X-ray diffractometer.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
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Issue or Number:4
Record Number:CaltechAUTHORS:20130417-093946134
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Official Citation:John M. Hughes, Andreas Ertl, Heinz-Jürgen Bernhardt, George R. Rossman, and John Rakovan Mn-rich fluorapatite from Austria: Crystal structure, chemical analysis, and spectroscopic investigations American Mineralogist, April, v. 89, p. 629-632
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37981
Deposited By: Ruth Sustaita
Deposited On:17 Apr 2013 22:21
Last Modified:03 Oct 2019 04:53

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