Crystallographic analysis reveals pseudo-merohedral twinning in sardashtite and proto-owyheeite, highlighting easier structural determination than in owyheeite.
The As-containing proto-owyheeite [Ag 2.26(07) Cu 0.14(01) Tl 0.13(03) Pb 9.40(06) Sb 10.96(07) As 0.38(02) S 28 , P 2 1 / n , a = 8.1696 (2) Å, b = 27.3377 (4) Å, c = 22.8584 (4) Å, β = 90.078 (2)°, V = 5105.15 (17) Å 3 ] and sardashtite [Ag 2.23(06) Cu 0.65(02) Pb 10.34(07) Sb 8.96(13) As 1.83(02) S 28 , P 2 1 / n , a = 8.2038 (3) Å, b = 27.1002 (10) Å, c = 22.7885 (9) Å, β = 90.1850 (10)°, V = 5066.4 (3) Å 3 ] crystallize as twofold superstructures (doubling of the a -axis with respect to a hypothetical basic structure), which are closely related to the structure of owyheeite. In contrast to owyheeite, which features systematic (approximate) cyclic twinning by 120° rotation about [100], proto-owyheite and sardashtite are twinned by pseudo-merohedry (reflection at [100] or equivalently [001]), which made structural elucidation significantly less troublesome.
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Stöger et al. (2026) studied this question.
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