Abstract

Rouseite, ideally Pb2Mn(AsO3)2·2H2O, is a new mineral species found associated with trigonite and finnemanite from Långban, Värmland, Sweden. Rouseite is triclinic, space group P1 or P1, with a = 6.36(2), b = 7.29(2), c = 5.54(2) Å, α = 97.3(3), β = 114.2(2), γ =106.0(2)°, V = 216.5 Å3, and Z = 1. The eight strongest reflections in the X-ray powder-difiraction pattern are (d,I/I0,hkl) 6.81,100,010; 3.38,60,020; 3.25,60,021,111; 3.06,70,211; 2.983,80,101; 2.849,90,121; 2.751,50,102; and 2.016,60,321.

Microprobe and thermogravimetric analyses gave PbO 59.6, MnO 10.0, As2O3 27.0, H2O 4.8, sum = 101.4 wt%, leading to the above formula. Rouseite is light yellow, with perfect {010} and {110} cleavages, density (calc.) = 5.70 g/cm3, hardness approximately 3 (Mohs). Optically, rouseite is biaxial (–), 2Vx = 46°, with strong dispersion of the optic axes, r > v, indices of refraction > 1.80, and maximum birefringence = 0.07. The name honors Dr. Roland Rouse of the University of Michigan.

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