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Fluorowardite, NaAl₃(PO₄)₂(OH)₂F₂·2H₂O, the fluorine analog of wardite from the Silver Coin mine, Valmy, Nevada

Kampf, Anthony R. and Adams, Paul M. and Housley, Robert M. and Rossman, George R. (2014) Fluorowardite, NaAl₃(PO₄)₂(OH)₂F₂·2H₂O, the fluorine analog of wardite from the Silver Coin mine, Valmy, Nevada. American Mineralogist, 99 (4). pp. 804-810. ISSN 0003-004X. doi:10.2138/am.2014.4663.

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Fluorowardite (IMA2012-016), NaAl₃(PO₄)₂(OH)₂F₂·2H₂O, the F analog of wardite, is a new mineral from the Silver Coin mine, Valmy, Iron Point district, Humboldt County, Nevada, U.S.A., where it occurs as a low-temperature secondary mineral in complex phosphate assemblages rich in Al, Na, and F. Fluorowardite forms colorless to white or cream-colored, tetragonal-pyramidal crystals up to 0.1 mm in diameter. The streak is white. Crystals are transparent to translucent, with vitreous to pearly luster. The Mohs hardness is about 5, the tenacity is brittle, the fracture is irregular, and crystals exhibit one perfect cleavage on {001}. The calculated density is 2.760 g/cm³. Optically, fluorowardite is uniaxial positive, with ω = 1.576(2) and ɛ = 1.584(2) (white light) and is non-pleochroic. Electron microprobe analyses (average of 8) provided: Na₂O 6.27, CaO 1.74, MgO 0.42, Al₂O₃ 35.21, Fe₂O₂ 0.72, P₂O₅ 32.49, As₂O₅ 0.64, F 6.76, O=F −2.85, H₂O 13.35 (structure), total 94.74 wt%. The presence of H₂O and OH and the absence of CO₃ were confirmed by FTIR spectroscopy. The empirical formula (based on 14 anions) is: Na_(0.87)Ca_(0.13)Mg_(0.04))_(∑1.04)(Al_(2.96)Fe^(3+)_(0.04))_(∑3.00)(P_(1.96)As_(0.03))_(∑1.99)O_(8.12)(OH)_(2.35)F_(1.53)·2H_2O. Fluorowardite is tetragonal, P4_12_12, ɑ = 7.077(2), c = 19.227(3) Å, V = 962.8(5) Å^3, and Z = 4. The eight strongest lines in the X-ray powder diffraction pattern are [d_(obs) in Å(I)(hkl)]: 4.766(100)(004,103); 3.099(75)(211,203); 3.008(62)(115,212); 2.834(28)(204,213); 2.597(56)(205); 1.7628(32)(400,401); 1.6592(29)(multiple); and 1.5228(49)(423, 2·2·10). The structure of fluorowardite (R_1 = 3.15% for 435 F_o > 4σF) contains layers parallel to {001} consisting of Alϕ₆ (ϕ = F, O, OH or H₂O) octahedra, PO₄ tetrahedra, and NaO₆(H₂O)₂ polyhedra. The two independent Alϕ₆ octahedra link by corner-sharing to form a square array. Each PO4 tetrahedron shares corners with three adjacent octahedra in the same square array and a fourth corner with an octahedron in the next layer. The Na atoms reside in the “cavities” in the square array, forming bonds only to O atoms in the same layer. Of the two nearly identical OH sites in the wardite structure, only one is occupied by F in the fluorowardite structure. This is an interesting example of a structure in which OH and F are selectively incorporated into two different, but similar, sites as the result of rather subtle hydrogen bonding influences.

Item Type:Article
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URLURL TypeDescription Data
Kampf, Anthony R.0000-0001-8084-2563
Rossman, George R.0000-0002-4571-6884
Additional Information:© 2014 Mineralogical Society of America. Manuscript received July 9, 2013. Manuscript accepted October 7, 2013. Manuscript handled by G. Diego Gatta. Reviewers Stuart Mills and Frédéric Hatert and Editor Keith Putirka are thanked for their constructive comments on the manuscript. Work at the California Institute of Technology was supported by grants from the Northern California Mineralogical Association and the National Science Foundation (EAR-0947956). 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.
Group:Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Northern California Mineralogical AssociationUNSPECIFIED
John Jago Trelawney EndowmentUNSPECIFIED
Subject Keywords:Fluorowardite; new mineral; crystal structure; hydrogen bonding; FTIR spectroscopy; Raman spectroscopy; electron microprobe analysis; Silver Coin mine, Valmy, Nevada
Issue or Number:4
Record Number:CaltechAUTHORS:20140519-133338710
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Official Citation:Anthony R. Kampf, Paul M. Adams, Robert M. Housley, and George R. Rossman Fluorowardite, NaAl3(PO4)2(OH)2F2·2H2O, the fluorine analog of wardite from the Silver Coin mine, Valmy, Nevada American Mineralogist, , v. 99, p. 804-810, doi:10.2138/am.2014.4663
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45827
Deposited By: Ruth Sustaita
Deposited On:19 May 2014 22:10
Last Modified:21 Feb 2023 23:18

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