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Fluorowardite, NaAl_3(PO_4)_2(OH)_2F_2·2H_2O, 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, NaAl_3(PO_4)_2(OH)_2F_2·2H_2O, the fluorine analog of wardite from the Silver Coin mine, Valmy, Nevada. American Mineralogist, 99 (4). pp. 804-810. ISSN 0003-004X. http://resolver.caltech.edu/CaltechAUTHORS:20140519-133338710

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Abstract

Fluorowardite (IMA2012-016), NaAl_3(PO_4)_2(OH)_2F_2·2H_2O, 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/cm^3. 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: Na_2O 6.27, CaO 1.74, MgO 0.42, Al_2O_3 35.21, Fe_2O_3 0.72, P_2O_5 32.49, As_2O_5 0.64, F 6.76, O=F −2.85, H_2O 13.35 (structure), total 94.74 wt%. The presence of H_2O and OH and the absence of CO_3 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 Alϕ_6 (ϕ = F, O, OH or H_2O) octahedra, PO_4 tetrahedra, and NaO_6(H_2O)_2 polyhedra. The two independent Alϕ_6 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
Related URLs:
URLURL TypeDescription
http://ammin.geoscienceworld.org/content/99/4/804.abstractPublisherArticle
http://dx.doi.org/10.2138/am.2014.4663DOIArticle
http://www.minsocam.org/MSA/AmMin/TOC/2014/Apr2014_data/Apr2014_data.htmlOtherSupplementary Data Info
ORCID:
AuthorORCID
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.
Funders:
Funding AgencyGrant Number
Northern California Mineralogical AssociationUNSPECIFIED
NSFEAR-0947956
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
Record Number:CaltechAUTHORS:20140519-133338710
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140519-133338710
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
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:19 May 2014 22:10
Last Modified:06 Feb 2017 19:46

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