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Pararsenolamprite, a new polymorph of native As, from the Mukuno mine, Oita Prefecture, Japan

Published online by Cambridge University Press:  05 July 2018

S. Matsubara ,
R. Miyawaki ,
M. Shimizu  and
T. Yamanaka
S. Matsubara*
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunincho, Shinjuku, Tokyo 169-0073, Japan
R. Miyawaki
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunincho, Shinjuku, Tokyo 169-0073, Japan
M. Shimizu
Affiliation:
Department of Earth Sciences, Faculty of Science, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
T. Yamanaka
Affiliation:
Chuo-cho 2-5-20, Nakatsu, Oita 871-0024, Japan
*
*E-mail: [email protected]
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Abstract

Pararsenolamprite, the third polymorph of native As, is found at the Mukuno mine, Oita Prefecture, Japan. It is orthorhombic, Pmn21 or P21nm, a = 3.633(2), b = 10.196(2), c= 10.314(2)Å, Z = 18. The seven strongest lines in the X-ray powder diffraction pattern are: 5.17 (100) (002), 4.60 (24) (012), 3.259 (58) (013), 2.840 (27) (032), 2.580 (22) (004), 2.299 (23) (024), and 1.794 (26) (105). Electron microprobe analysis gives As 91.89, Sb 7.25, S 0.48, total 99.62 wt.% (mean of 8), and lead to the empirical formula, As0.96Sb0.03S0.01. It is lead grey in colour and opaque with metallic lustre and black streak. It is sectile and brittle with perfect cleavage on [001]. The VHN25 is 66–91 kg/mm2, corresponding to 2–2.5 in Mohs' hardness scale. The measured and calculated densities are 5.88(5) g/cm3 and 6.01 g/cm3, respectively. In reflected plane-polarized light in air, it is white with a slightly greenish blue tint. Anisotoropy is strong, dark brown to dark greenish grey. Bireflectance is distinct; parallel to elongation it is creamy; perpendicular to elongation it is brown, grey and green. Internal reflections are absent. The reflectance spectra are tabulated in the text.

Pararsenolamprite occurs as euhedral crystals in close association with arsenic, stibnite and quartz in a Sb-As-Ag-Au-bearing quartz vein cutting altered Neogene andesite from the Mukuno mine. It forms radial or parallel aggregates of bladed cystals up to 0.8 mm in length.

Keywords

pararsenolampritearsenicpolymorphnew mineralMukuno mineX-raychemistryoptical data
Type
Research Article
Information
Mineralogical Magazine , Volume 65 , Issue 6 , December 2001 , pp. 807 - 812
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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