Pete J. Dunn2,
of Mineral Sciences, American Museum of Natural History,
New York, New York 10024, U.S.A.
of Mineral Sciences, TSmithsonian Institution
Washington, DC 20560, U.S.A.
of Geological and Planetary Sciences, 170-25,
California Institute of Technology,
Pasadena, California 91125, U.S.A.
Gamagarite from Postmasburg district, Cape Province, Republic
South Africa is re-examined using analytical chemistry, infrared
spsectra, and X-ray diffraction techniquies. The data incicate that
gamagarite is isostructural with brackebuschite: space group P21/m (assumed
symmetry) with unit
cell constants a
= 9.15(1), b
= 6.17(1), c
= 7.88(1)Å, β = 112.7(2)°. Infrared spectra indicate
that strongly hydrogen-bonded OH- is the
hydrogen-bearing species in both gamagarite and brackebuschite.
Consequently, with a reevaluation of previously poublikshed structure
data, our interpretation prefers the brackebuschite-type structure as a
partically acid vanadate (arsenate and phosphate) containing HVO42--type
units rather than as a hydrated vanadate containing structural water,
as previously described. However, there are uncertainties with the
assignment of Mn oxidation state.