Aurihydrargyrumite, a Natural Au 6 Hg 5 Phase from Japan

摘要

Aurihydrargyrumite, a natural Au 6 Hg 5 phase, was found in Iyoki, Uchiko, Ehime Prefecture, Shikoku Island, Japan. Aurihydrargyrumite with a metallic silver luster occurs as a submicron- to 2 μm-thick layer on the outermost surface of the placer gold. A prismatic face may be formed by {001} and {100} or {110}. The streak is also silver white and its Mohs hardness value is ca. 2.5. Its tenacity is ductile and malleable, and its density, as calculated based on the empirical formula and powder unit-cell data, is 16.86 g·cm ?3 . The empirical formula of aurihydrargyrumite, on the basis of 11 Au + Hg, is Au 5.95 Hg 5.05 . Aurihydrargyrumite is hexagonal, P 6 3 / mcm , with the lattice parameters a = 6.9960(10) ?, c = 10.154(2) ? and V = 430.40(15) ? 3 , which is identical with the synthetic Au 6 Hg 5 phase. The seven strongest lines in the powder X-ray diffraction (XRD) pattern [ d in ?( I / I 0 )( hkl )] were 2.877(29)(112), 2.434(42)(113), 2.337(100)(104), 2.234(87)(211), 1.401(39)(314), 1.301(41)(404), and 1.225(65)(217). Aurihydrargyrumite forms through the weathering of mercury-bearing placer gold by involvement of self-electrorefining. This new mineral has been approved by the IMA-CNMNC (2017-003) and it is named for its composition, being a natural amalgam of gold (Latin: aurum) and mercury (Latin: hydrargyrum).