Jarosewichite, Mn3+Mn32+(AsO4)(OH)6, is a new mineral, closely related to chlorophoenicite, from the Franklin mine, Franklin, Sussex County, New Jersey, where it occurs associated with andradite, franklinite, flinkite, cahnite and hausmannite. Jarosewichite is orthorhombic, space group C2/m2/m2/m, C222 or Cmm2, with a = 6.56(3), b = 25.20(10), c = 10.00(5)Å, and Z = 8. The strongest lines in the X-ray powder diffraction pattern are (d, I, hkl) 2.669 100 222,082; 3.91 60 042, 061; 1.788 50 (not indexed); 2.503 30 242, 261, 004, 0 10 0. Jarosewichite is dark red, occurs in prismatic barrel-shaped aggregates, has a density of 3.66 (obs), 3.70 g/cm3 (calc). It is biaxial (—) with refractive indices α = 1.780(5), β = 1.795(5) and γ = 1.805(5); the orientation is X = a, Y = b, Z = c; pleochroism is weak, Z > X. Microprobe analysis with Mn3+ calculated, yields: FeO 0.4, MgO 2.1, CaO 0.2, ZnO 1.2, MnO 42.3, Mn2O3 17.7 (ΣMn = 45.1 wt.%), As2O5 24.0, with H2O 12.1 percent by difference, sum = 100.0 percent.

A second manganese arsenate from Franklin, New Jersey, is also related to chlorophoenicite, but may be heterogeneous. Although optical, chemical and crystallographic properties are characterized, there is sufficient ambiguity to deny it species status at this time. The data for this mineral, jarosewichite and chlorophoenicite imply the existence of a large family of related arsenates based on the structure principles outlined by Moore for chlorophoenicite.

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