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Angarfite, NaFe^(3+)_5(PO_4)_4(OH)_(4)·4H_2O, a New Mineral Species from the Angarf-Sud Pegmatite, Morocco: Description and Crystal Structure

Kampf, Anthony R. and Mills, Stuart J. and Housley, Robert M. and Favreau, Georges and Boulliard, Jean-Claude and Bourgoin, Vincent (2012) Angarfite, NaFe^(3+)_5(PO_4)_4(OH)_(4)·4H_2O, a New Mineral Species from the Angarf-Sud Pegmatite, Morocco: Description and Crystal Structure. Canadian Mineralogist, 50 (4). pp. 781-791. ISSN 0008-4476. doi:10.3749/canmin.50.4.781.

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Angarfite, ideally NaFe^(3+)_5(PO_4)_4(OH)_(4·)4H_2O, is a new mineral from the Angarf-Sud pegmatite, Tazenakht, Ouarzazate Province, Souss-Massa-Draâ region, Morocco. The mineral occurs on etched surfaces of triphylite in association with lipscombite–barbosalite, jahnsite-(NaFeMg) and bederite. It is interpreted as having resulted from the reaction of Na-bearing hydrothermal solutions with primary triphylite. The crystals are orange-brown to red-brown needles and prisms, elongate on [001], with poorly formed chisel-like terminations. The mineral is transparent and has a pale brown streak, a vitreous luster, a Mohs hardness of approximately 2½, a splintery fracture and one poorly developed cleavage on {010}. It is brittle, but thin needles are slightly flexible. The measured and calculated densities are 2.76(3) and 2.771 g/cm^3, respectively. It is optically biaxial (+),α 1.688(1), β 1.696(1), γ 1.708(2) (white light); 2V_(meas) = 80(3)°; 2V_(calc) = 79°; strong r > v dispersion; optical orientation: X = b, Y = c, Z = a; pleochroism: X is tan, Y, medium red-brown, and Z, dark red-brown, with X < Y < Z. The average results of five electron-microprobe analyses gave Na_2O 2.69, MgO 4.76, Mn_2O_3 1.79, Fe_2O_3 37.36, P_2O_5 34.68, H_2O 14.63 (from structure refinement), total 95.91 wt%. The empirical formula, based on 24 O atoms, is Na_(0.71)(Fe^(3+)_(3.83)Mg_(0.97)Mn^(3+)_(0.19))Σ_(4.99)(P_(1.00)O_4)_4(OH)_(2.71)(H_2O)_(1.29·)4H_2O. Angarfite is orthorhombic, C222_1, ɑ 12.7997(3), b 17.9081(4), c 8.2112(6) Å, V 1882.16(15) Å^3 and Z = 4. The eight strongest lines in the X-ray powder-diffraction pattern [d_(obs) in Å(I)(hkl)] are: 10.463(43)(110), 9.016(100)(020), 6.459(42)(111), 3.731(27)(022), 3.355(51)(241), 3.026(29)(042), 1.926(33)(462, 263), 1.463(36)(822, 663, 4102, 2103). The crystal structure (R_1 = 3.02% for 2074 reflections, F_o > 4σF) contains zig-zag chains of edge-sharing Fe^(3+)O_6 octahedra along c, which are linked into sheets parallel to {010} by sharing corners with octahedra in adjacent chains and by sharing corners with peripheral PO_4 tetrahedra. Insular octahedra between the sheets share two sets of cis corners with tetrahedra in adjacent sheets, thereby linking the sheets into a framework. Channels in the framework parallel to c contain a partially occupied Na site and a disordered H_2O site. Identical sheets of octahedra and tetrahedra are found in the structures of bakhchisaraitsevite and mejillonesite.

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Kampf, Anthony R.0000-0001-8084-2563
Additional Information:© 2012 Mineralogical Association of Canada. Received June 16, 2011, revised manuscript accepted June 4, 2012. The manuscript benefitted from comments by reviewers Frédéric Hatert and Kim Tait. We also acknowledge the very able shepherding of the manuscript by Associate Editor Miguel Galliski and the astute editing of Editor-in-Chief Robert F. Martin. The EMP 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. Finally, we wish to pay special tribute to Petr Černý for ground-breaking contributions to the understanding of pegmatites.
Funding AgencyGrant Number
Northern California Mineralogical AssociationUNSPECIFIED
Natural History Museum of Los Angeles County John Jago Trelawney EndowmentUNSPECIFIED
Subject Keywords:angarfite, new mineral species, phosphate, crystal structure, bakhchisaraitsevite, mejillonesite, Angarf-Sud pegmatite, Morocco.
Issue or Number:4
Record Number:CaltechAUTHORS:20130403-100345038
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Official Citation:Angarfite, NaFe3+5(PO4)4(OH)4·4H2O, a New Mineral Species from the Angarf-Sud Pegmatite, Morocco: Description and Crystal Structure Anthony R. Kampf, Stuart J. Mills, Robert M. Housley, Georges Favreau, Jean-Claude Boulliard, and Vincent Bourgoin Can Mineral 2012 50:781-791; doi:10.3749/canmin.50.4.781
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37740
Deposited By: Ruth Sustaita
Deposited On:03 Apr 2013 17:43
Last Modified:09 Nov 2021 23:31

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