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Ca2Mn(AsO4)2.2H2O
Monoclinic
Brandtite was reported from Sterling Hill by Gaines (1959); it has not been found at Franklin.
Brandtite occurs in elongate prismatic crystals; some are lath-like. They are up to 0.3 mm in length and commonly form radiating aggregates, but may occur randomly oriented; clusters up to 12 mm have been found. Brandtite is commonly colorless, but may be light brown or light yellow; it is easily stained. Cleavage is perfect on {010} and good on {001}. Optically, brandtite is biaxial, positive, 2V approximately 15o, with b = 1.7070 and g = 1.7215; dispersion is very strong, r < v (Gaines, 1959). There is no discernible fluorescence in ultraviolet. It can be confused with some chlorophoenicite; X-ray methods are best for verification.
Brandtite is a calcium manganese arsenate hydrate mineral. A partial analysis by the writer of a specimen from the black-willemite ore is given in Table 25 and shows minimal substitution of Fe or Mg; Zn was not determined. Brandtite from the red-willemite ore has Mn >> Mg and, as shown by Parker and Troy (1982), the arsenates from the red ore are predominantly Mn and Mg rich.
The original 1940 find of Sterling Hill brandtite was between the 1400 and 1500 levels and was in the black-willemite zone “near a point where over-breakage had trespassed slightly into the adjacent brown willemite” (Gaines, 1959). This brandtite was associated with rhodochrosite and chalcopyrite in a matrix of calcite, franklinite, brown willemite, and sphalerite.
Additional occurrences of brandtite in the black-willemite zone have been recorded on the 1480, 1500, and 1600 levels, where it is associated with sphalerite, willemite, barite, loellingite and quartz. Brandtite is also found on the 1400 level in white to light brown sheave-like aggregates with sarkinite on a red-willemite matrix. It also occurs in white acicular sprays, associated with willemite, about 50 feet above the 1000 level, in the east branch of the west limb.
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| Copyright © 1995 by Pete J. Dunn |
Website
by Herb Yeates
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Link
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This
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