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Tsugaruite, Pb4As2S7, a new mineral species from the Yunosawa mine, Aomori Prefecture, Japan

Published online by Cambridge University Press:  05 July 2018

M. Shimizu ,
R. Miyawaki ,
A. Kato ,
S. Matsubara ,
F. Matsuyama  and
K. Kiyota
M. Shimizu
Affiliation:
Department of Earth Sciences, Faculty of Science, Toyama University, Gofuku 3190, Toyama 930-8555, Japan
R. Miyawaki
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku, Tokyo 169-0073, Japan
A. Kato
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku, Tokyo 169-0073, Japan
S. Matsubara
Affiliation:
Department of Geology, National Science Museum, 3-23-1 Hyakunin-cho, Shinjuku, Tokyo 169-0073, Japan
F. Matsuyama
Affiliation:
Department of Petrology & Mineral Deposits, University Museum, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
K. Kiyota
Affiliation:
Department of Earth & Planetary Physics, Faculty of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
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Abstract

Tsugaruite, Pb4As2S7, is a new Pb-As sulphosalt from the Yunosawa mine, Aomori Prefecture, northern Japan. X-ray studies indicated it to be orthorhombic Pnn2 or Pnnm, a 15.179(1), b 38.195(1), c 8.0745(1) Å, Z = 16 [Pb4As2S7] with a subcell with c′ = 1/2c. The six strongest diffractions in the X-ray powder pattern [d (in Å), (I), (hkl)] are: 4.47 (30) (340), 3.705 (34) (1.10.0), 3.395 (100) (450), 2.870 (34) (192), 2.819 (53) (550), and 2.739 (48) (560, 2.13.0). The average of seven electron microprobe analyses gave Pb 68.70, Tl 0.13, As 12.45, S 18.64, total 99.92 wt.%. The empirical formula calculated on the basis of total atoms = 13 is Pb3.99Tl0.01As2.00S7.00, corresponding to the ideal formula Pb4As2S7. The calculated density is 6.83 g/cm3 for the ideal formula.

Tsugaruite is opaque with a metallic lustre and lead-grey streak. No cleavage was observed. It is brittle with uneven fracture. VHN25 is 75.4–94.9 kg/mm2, mean 86.4 (n) = 4), corresponding to 2.5–3 in Mohs' hardness scale. In reflected plane-polarised light in air, it is white with a greenish tint, more greenish than jordanite. Bireflectance and pleochroism are weak, weaker than those of jordanite; and anisotropism is weak to moderate, weaker than that of jordanite. No internal reflections. The reflectance spectra are tabulated in the text.

Tsugaruite was found in a thin baryte veinlet exposed in the wall of a small open cut of the Yunosawa mine. It forms radiating groups of long tabular tapering crystals elongated along c and tabular to b, up to 0.04 mm wide and 2 mm long. The associated minerals are jordanite, which formed earlier than tsugaruite, and galena. The chemical similarity of tsugaruite and jordanite and their intergrown character indicates that earlier jordanite analyses may also include analyses of tsugarite.

Keywords

tsugaruitejordantenew mineralYunosawa mineAomori PrefectureJapanX-raychemicaland optical data
Type
Research Article
Information
Mineralogical Magazine , Volume 62 , Issue 6 , December 1998 , pp. 793 - 799
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1998

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