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Fluorphosphohedyphane, Ca_2Pb_3(PO_4)_3F, the first apatite supergroup mineral with essential Pb and F

Kampf, Anthony R. and Housley, Robert M. (2011) Fluorphosphohedyphane, Ca_2Pb_3(PO_4)_3F, the first apatite supergroup mineral with essential Pb and F. American Mineralogist, 96 (2-3). pp. 423-429. ISSN 0003-004X.

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The new mineral fluorphosphohedyphane, Ca_2Pb_3(PO_4)_3F, the F-analog of phosphohedyphane, is hexagonal with space group P6_3/m and cell parameters a = 9.6402(12), c = 7.0121(8) Å, V = 564.4(1) Å^3, and Z = 2. It occurs in the oxidation zone of a small Pb-Cu-Zn-Ag deposit, the Blue Bell claims, about 11 km west of Baker, San Bernardino County, California. It forms as sub-parallel intergrowths and irregular clusters of transparent, colorless, highly lustrous, hexagonal prisms with pyramidal terminations. It is found in cracks and narrow veins in a highly siliceous hornfels in association with cerussite, chrysocolla, fluorite, fluorapatite, goethite, gypsum, mimetite, opal, phosphohedyphane, plumbogummite, plumbophyllite, plumbotsumite, pyromorphite, quartz, and wulfenite. The streak of the new mineral is white, the luster is subadamantine, and the Mohs hardness is about 4. The mineral is brittle with subconcoidal fracture and no cleavage. The calculated density is 5.445 g/cm^3 based upon the empirical formula. Optical properties (589 nm): uniaxial (–),ω= 1.836(5), ε= 1.824(5), nonpleochroic. SEM-EDS analyses yielded the averages and ranges in wt%: O 21.28 (20.31–22.14), F 1.59 (1.38–1.91), P 10.33 (9.81–10.83), Ca 9.66 (8.97–10.67), Pb 60.08 (57.67–61.21), total 102.95 (102.02–103.88), providing the empirical formula (based on P = 3): Ca2.00(Pb_(2.61)Ca_(0.17)) Σ_(2.78)P_3O_(11.91)F_(0.75). Infrared spectroscopy showed no evidence of OH or carbonate. The strongest powder X-ray diffraction lines are [d(hkl)I]: 8.38(100)22, 3.974(111)28, 3.506(002)25, 2.877(121,211)100, 1.878(213,123)26. Fluorphosphohedyphane has the apatite structure (R_1 = 1.75% for 444 reflections with F_o > 4 F) with ordering of Ca and Pb in two cation sites, as in hedyphane and phosphohedyphane. The Pb^(2+) cation exhibits a stereoactive 6s^2 lone-electron-pair. The X anion site at (0, 0,1/2) is fully occupied by F forming six bonds of 2.867 Å to Pb atoms, in contrast to the six Pb-Cl bonds of 3.068 Å in phosphohedyphane.

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Kampf, Anthony R.0000-0001-8084-2563
Additional Information:© 2011 Mineralogical Society of America. Manuscript received April 21, 2010; Manuscript accepted September 9, 2010; Manuscript handled by Rhian Jones. John M. Hughes and Stuart J. Mills provided helpful comments on the manuscript. Associate Editor, Rhian Jones is especially thanked for pointing out the need to look more critically at the F analyses. Joseph Marty of Salt Lake City, Utah, is thanked for providing the specimens of fluorphosphohedyphane used in this study. The IR spectroscopy was conducted in the laboratory of George R. Rossman at the California Institute of Technology and with his assistance. The SEM/EDS studies and the microprobe analyses were supported by a grant to Caltech from the Northern California Mineralogical Association. The remainder of this study was funded by the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County.
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Northern California Mineralogical AssociationUNSPECIFIED
John Jago Trelawney EndowmentUNSPECIFIED
Subject Keywords:Fluorphosphohedyphane; new mineral; crystal structure; apatite supergroup; hedyphane group; Pb2+ 6s(2) lone-electron-pair; Blue Bell claims; California
Issue or Number:2-3
Record Number:CaltechAUTHORS:20110307-133810267
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22696
Deposited By: Tony Diaz
Deposited On:08 Mar 2011 18:26
Last Modified:09 Mar 2020 13:18

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