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Mn3+Mn2+3(AsO4)(OH)6
Orthorhombic, C2/m2/m2/m, C222, or Cmm2,
a = 6.56, b = 25.20, c = 10.00 Ĺ, Z = 8
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| Figure 25-28. Divergent prismatic clusters of stout jarosewichite crystals with platy flinkite crystals from Franklin. Field of view is 0.6 mm in maximum dimension. | ||
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Jarosewichite was described from Franklin by Dunn et al. (1982b); it has not been found at Sterling Hill. The crystal structure is unknown.
Jarosewichite occurs in barrel-shaped, prismatic crystals with a rough irregular surface; they resemble some Sterling Hill synadelphite. Such crystals form slightly radial aggregates (Figures 25-28 and 25-29). Crystals are 0.5-1.0 mm in length, elongate on [100], and slightly tabular on [010]; {010} is the dominant form, with {021} subordinate in development. Jarosewichite is very dark red, nearly black to the eye, with subvitreous luster, a density of 3.66 g/cm3, and an apparent lack of cleavage. It is best verified using X-ray methods. Additional descriptive information was provided by King (1993).
Optically, jarosewichite is biaxial, negative, with 2V (calc.) = 78o; a = 1.780, b = 1.795, and g = 1.805; weak pleochroism with Z = dark brownish red and X = medium brownish red; and absorption Z > X.
Jarosewichite is a manganese arsenate hydroxide mineral related to chlorophoenicite. A microprobe analysis is given in Table 25. The oxidation state of Mn is inferred, as discussed in detail by Dunn et al. (1982b)
Jarosewichite occurs on one specimen collected on the dumps. It was reported by Cook (1973) to be carminite, which is unknown locally. Subsequent investigation of this purported “carminite” resulted in the discovery that it was a new mineral, jarosewichite. The matrix is vuggy ore consisting of massive green andradite and manganoan franklinite.
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| Figure 25-29. Stout, barrel-shaped radiating crystals of jarosewichite from Franklin, associated with platy flinkite (left) and cahnite (right). Field of view is 1.2 mm in maximum dimension. | ||
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The vugs are lined with a poorly crystalline friedelite-like mineral, which is in turn partially encrusted with hausmannite and coated cahnite crystals. These minerals are, in turn, coated partially with crystals of flinkite and jarosewichite (Figures 25-26, 25-28, and 25-29).
The name honors Eugene Jarosewich, chief mineral chemist at the Smithsonian Institution, in recognition of his contributions to chemical analytical procedures.
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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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