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BaFe3+8(AsO4)6(OH)8.14H2O
Tetragonal?
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| Figure 25-10. Equant, modified, pseudo- octahedral crystal of barium-pharmacosiderite from Sterling Hill. Field of view is 0.3 mm in maximum dimension. | ||
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Barium-pharmacosiderite, a barium ferric-iron arsenate hydroxide hydrate mineral, was described from Sterling Hill by Peacor and Dunn (1985); it has not been found at Franklin. It occurs as deep yellow, 0.3 mm, equant crystals, which are rough-surfaced and pseudo-octahedral in habit (Figure 25-10).
The luster of barium-pharmacosiderite is vitreous. The observed ratio of Ba:Fe:As is 0.8:7.6:6.0. It occurs rarely on the 340 level at Sterling Hill on younger pharmacosiderite, which overlies ogdensburgite.
Another yellow pharmacosiderite, occurring in 1 mm, yellow, cubic to pseudoprismatic crystals, was found at Sterling Hill, and preserved by John Baum, but is not properly any of the known mineral species in the pharmacosiderite series. Sr is the dominant large cation, but appreciable amounts of Pb, Mn, and Zn are also present; it is chemically inhomogeneous. The compositional range for Pb and Sr is PbO 3.4-7.4, SrO 1.8-3.1 wt. %; other cations present (Ba,Ca,Zn,Fe, As,Mn) are relatively invariant. It occurs associated with willemite, koettigite, and sphalerite in a vein assemblage.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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Link
to homepage
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This
page created: January 11, 2001 |
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