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 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