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Alcaparrosaite, K_3Ti^(4+)Fe^(3+)(SO_4)_4O(H_2O)_2, a new hydrophobic Ti^(4+) sulfate from Alcaparrosa, Chile

Kampf, A. R. and Mills, S. J. and Housley, R. M. and Williams, P. A. and Dini, M. (2012) Alcaparrosaite, K_3Ti^(4+)Fe^(3+)(SO_4)_4O(H_2O)_2, a new hydrophobic Ti^(4+) sulfate from Alcaparrosa, Chile. Mineralogical Magazine, 76 (4). pp. 851-861. ISSN 0026-461X. doi:10.1180/minmag.2012.076.4.03.

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Alcaparrosaite, ideally K_3Ti^(4+)Fe^(3+)(SO_4)_4O(H_2O)_2, is a new mineral from the Alcaparrosa mine, Cerritos Bayos, El Loa Province, Antofagasta, Chile (IMA2011-024). The mineral occurs on and intergrown with coquimbite, and is also associated with ferrinatrite, krausite, pertlikite, pyrite, tamarugite and voltaite. It is a relatively early phase which forms during the oxidation of pyritic masses under increasingly arid conditions. Alcaparrosaite crystallizes from hyperacidic solutions in a chemical environment that is consistent with its association with coquimbite. It occurs as pale yellow blades and tapering prisms up to 4 mm in length, flattened on {010} and elongated along [100]. The observed crystal forms are {010}, {110}, {1.13.0} and {021}. The mineral is transparent and has a white streak, vitreous lustre, Mohs hardness of about 4, brittle tenacity, conchoidal fracture and no cleavage. The measured and calculated densities are 2.80(3) and 2.807 g cm^(−3), respectively. It is optically biaxial (+) with α = 1.643(1), β = 1.655(1), γ = 1.680(1) (white light), 2V_(meas) = 70(2)° and 2V_(calc) = 70.3°. The mineral exhibits strong parallel dispersion, r < v. The optical orientation is X = b; Y^^_c = 27° in the obtuse angle β. No pleochroism was observed. Electron-microprobe analyses (average of 4) provided: Na_2O 0.32, K_2O 20.44, Fe_2O_3 11.58, TiO_2 11.77, P_2O_5 0.55, SO_3 47.52, H_2O 5.79 (calc); total 97.97 wt.%. The empirical formula (based on 19 O) is (K_(2.89)Na_(0.07))_(Σ2.96)Ti^(4+)_(0.98)Fe^(3+)_(0.97)(S_(0.99)P_(0.01)O_4)_4O_(0.72) (OH)_(0.28)(H_2O)_2. The mineral is hydrophobic, insoluble in cold and hot water, very slowly soluble in acids and decomposes slowly in bases. Alcaparrosaite is monoclinic, C2/c, with the cell parameters α = 7.55943(14), b = 16.7923(3), c = 12.1783(9) Å, β = 94.076(7)°, V = 1542.01(12) Å^3 and Z = 4. The eight strongest lines in the X-ray powder diffraction pattern [d_(obs) in Å (I_(rel)) (hkl)] are 6.907 (41)(021,110); 3.628 (34) (023,1İ13); 3.320 (32) (21İ02); 3.096 (100) (202,1İ33,150); 3.000 (40) (1İ51);> 2.704 (38) (2İ23,152); 1.9283 (30) (1İ55); 1.8406 (31) (3İ53,206). In the structure of alcaparrosaite (R_1 = 2.57% for 1725 F_o > 4σF), Ti^(4+) and Fe^(3+), in roughly equal amounts, occupy the same octahedrally coordinated site. Octahedra are linked into dimers by corner sharing. The SO_4 tetrahedra link the dimers into chains parallel to [001] and link the chains into undulating sheets parallel to {010}. The sheets link via 10- and 11-coordinated K atoms in the interlayer region. The structure shares some features with that of goldichite.

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Kampf, A. R.0000-0001-8084-2563
Additional Information:© 2012 The Mineralogical Society. Received 28 September 2011; Accepted 19 December 2011; Associate Editor: G. Diego Gatta. Reviewers Elena Sokolova and Fernando Cámara are thanked for their constructive comments on the manuscript. Arturo Molina is thanked for providing the specimens of alcaparrosaite. The EMP analyses were supported by a grant to the California Institute of Technology 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.
Funding AgencyGrant Number
Northern California Mineralogical AssociationUNSPECIFIED
John Jago Trelawney EndowmentUNSPECIFIED
Subject Keywords:alcaparrosaite, new mineral, hydrous sulfate, crystal structure, hydrophobic, Alcaparrosa mine, Chile.
Issue or Number:4
Record Number:CaltechAUTHORS:20120925-104223563
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Official Citation:A. R. Kampf, S. J. Mills, R. M. Housley, P. A. Williams, and M. Dini Alcaparrosaite, K3Ti4+Fe3+(SO4)4O(H2O)2, a new hydrophobic Ti4+ sulfate from Alcaparrosa, Chile Mineralogical Magazine, August 2012, v. 76, p. 851-861, published online 2 August 2012, doi:10.1180/minmag.2012.076.4.03
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34344
Deposited By: Ruth Sustaita
Deposited On:25 Sep 2012 18:18
Last Modified:09 Nov 2021 23:07

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