Devitoite, a New Heterophyllosilicate With Astrophyllite-Like Layers


Anthony R. Kampf

Mineral Sciences Department, Natural History Museum of Los Angeles County
900 Exposition Boulevard, Los Angeles, CA 90007, U.S.A.

George R. Rossman

Division of Geological and Planetary Sciences,
California Institute of Technology, Pasadena, CA 91125-2500, U.S.A.

Ian M. Steele, Joseph J. Pluth

Department of the Geophysical Sciences, The University of Chicago
5734 S. Ellis Avenue, Chicago, IL 60637, U.S.A.

Gail E. Dunning

773 Durshire Way, Sunnyvale, CA 94087, U.S.A.

Robert E. Walstrolm

P.O. Box 1978, Silver City, NM 88062, U.S.A

Abstract

Devitoite, [Ba6(PO4)2(CO3)] [Fe2+7(OH)4Fe3+2O2(SiO3)8], is a new mineral from the Esquire #8 claim along Big Creek in eastern Fresno County, California, U.S.A. and is also found at the nearby Esquire #7 claim and at Trumbull Peak in Mariposa County. The mineral is named after 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 elongated and striated parallel to [100]. The mineral has cream to pale brown streak, silky luster, Mohs hardness of about 4, and two cleavages: {001} perfect and {010} good. The calculated density is 4.044 g/cm3. It is optically biaxial (–), α 1.710(6), β 1.735(3), γ 1.755(3), 2V (calc.) = 82.6°; orientation: Y = b, X ≈ c; Z ≈ a; pleochroism: brown, X >>>Y > Z. 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, and P2O5 4.84. Water and CO2 did not come from electron microprobe analysis. H2O 1.67, CO2 2.04 and FeO and Fe2O3 assignments were based on the structure.  Total analysis: 100.00 wt%. The empirical formula (based on 17 cations in the layer portion of the structure; Fe+Mg+Al+Si+Ti=17) is [(Ba5.453Ca0.193)(PO4)1.467O0.31(CO3)] [(Fe2+6.600Mg0.400)(OH)4(Fe3+1.639Ti4+0.216Al3+0.145)O2(Si7.513Al0.487O24)].

Devitoite is triclinic, P-1, a = 5.3437(7), b = 11.6726(15), c = 14.680(2)Å, α = 91.377(4)°, β = 96.757(4)°, γ = 103.233(4)°, V = 884.0(2) Å3, Z = 1. The crystal structure determination (R1 = 9.56% for 1370 Fo > 4sF) shows the mineral to be a heterophyllosilicate with astrophyllite-type HOH layers in which 5-coordinated Fe3+ takes the place of Ti4+. 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.

Devitoite Devitoite 2

Devitoite crystals about 150 micrometers wide.


Raman Spectrum: 100 to 1500 cm-1 (baseline corrected)

Raman Spectrum: 100 to 4000 cm-1 (raw spectrum, no corrections)



08-Dec-2010