DEVITOITE, A NEW HETEROPHYLLOSILICATE MINERAL WITH ASTROP

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• journal_title：The Canadian Mineralogist
• Contributor：Anthony R. Kampf ; George R. Rossman ; Ian M. Steele ; Joseph J. Pluth ; Gail E. Dunning ; Robert E. Walstrom
• Publisher：Mineralogical Association of Canada
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.48.1.29
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：48
• issue：1
• firstpage：29
• section：Articles

摘要

<p id="p-1">Devitoite, [Ba₆(PO₄)₂(CO₃)] [Fep>2+p>₇Fep>3+p>₂(Si₄O₁₂)₂O₂(OH)₄], is a new mineral species from the Esquire #8 claim along Big Creek in eastern Fresno County, California, U.S.A. It is also found at the nearby Esquire #7 claim and at Trumbull Peak in Mariposa County. The mineral is named for Alfred (Fred) DeVito (1937–2004). Devitoite crystallized very late in a sequence of minerals resulting from fluids interacting with a quartz–sanbornite vein along its margin with the country rock. The mineral occurs in subparallel intergrowths of very thin brown blades, flattened on {001} and elongate and striated parallel to [100]. The mineral has a cream to pale brown streak, a silky luster, a Mohs hardness of approximately 4, and two cleavages: {001} perfect and {010} good. The calculated density is 4.044 g/cmp>3p>. It is optically biaxial (+), α 1.730(3), β 1.735(6), γ 1.755(3); 2V_calc = 53.6°; orientation: X ≈ b, Y ≈ c, Z ≈ a; pleochroism: brown, Y >>> X > Z. Normalized electron-microprobe analyses provided: BaO 38.83, CaO 0.50, MgO 0.75, FeO 22.02, Fe₂O₃ 6.08, Al₂O₃ 1.50, SiO₂ 20.97, TiO₂ 0.80, P₂O₅ 4.84, H₂O 1.67, CO₂ 2.04, total 100.00 wt%, with FeO and Fe₂O₃ assignments and H₂O and CO₂ based on the structure. The empirical formula is [(Ba_5.45 Ca_0.19)_∑5.64(PO₄)_1.47O_0.30(CO₃)] [(Fep>2+p>_6.60Mg_0.40)_∑7(Fep>3+p>_1.64Tip>4+p>_0.22Alp>3+p>_0.14)_∑2(Si_7.51Al_0.49)_∑8O₂₆(OH)₄]. Devitoite is triclinic, P1̅, a 5.3437(7), b 11.6726(15), c 14.680(2) Å, α 91.337(4), β 96.757(4), γ 103.233(4)°, V 884.0(2) Åp>3p> and Z = 1. The crystal-structure determination (R₁ = 9.56% for 1370 F_o > 4σF) shows the mineral to be a heterophyllosilicate with astrophyllite-type HOH layers in which five-coordinated Fep>3+p> takes the place of Tip>4+p>. The interlayer region contains Ba atoms, PO₄ groups and CO₃ groups. The configuration of the Ba and PO₄ in the interlayer region is similar to that found in the structure of yoshimuraite. p>