Steverustite, Pb 2+ 5 (OH) 5 [Cu + (S 6+ O 3 S 2 –) 3 ](H 2 O) 2, a new thiosulphate mineral from the Frongoch Mine Dump, Devils Bridge, Ceredigion, Wal

  • Cooper M
  • Hawthorne F
  • Moffatt E
ISSN: 0026461X
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Abstract

Steverustite, ideally Pb2+5(OH)5[Cu+(S6+O3S2-)3](H2O)2, is a new supergene mineral from the Frongoch mine dump, Devils Bridge, Ceredigion, Wales. It generally forms fibrous fan-like bundles that occur in small cavities in quartz veins with other supergene species. Crystals are fibrous to acicular, elongated along [010], and are bounded by (h0l) faces too small to index reliably. It is transparent, colourless to white with a white streak, has a vitreous lustre, does not fluoresce under ultraviolet light and is brittle with a splintery fracture. The calculated density is 5.150 g/cm3, and the calculated mean refractive index is 1.94. The mineral is monoclinic, P21/n, a 12.5631(7), b 8.8963(5), c 18.0132(11) Å, β 96.459(1)°, V 2000.5(3) Å3, Z = 4, a:b:c = 1.41217:1:2.02480. The seven strongest lines in the X-ray powder diffraction pattern are as follows: d (Å), I, (h k l): 3.934, 10, (114); 3.934, 8,(111); 3.348, 7, (313); 6.211, 6, (200); 4.797, 6, (211); 3.026, 6, (314); 2.837, 5, (016). Chemical analysis by electron microprobe gave PbO 72.59, SO3 15.78, Cu2O 4.47, S2- 6.32, H2O 4.83, O=S2- -3.15, total 100.84 wt.% where the amount of H2O was determined by crystal-structure analysis. The resulting empirical formula is Pb2+4.99Cu+0.96(S6+O3S2-)3.03(OH)4.88(H2O)1.67, based on O + OH + H2O + S2- = 18.67 a.p.f.u. (atoms per formula unit) with H2O = 1.67 a.p.f.u. (from crystal-structure solution and refinement). The crystal structure of steverustite was solved by direct methods and refined to R1 = 2.7% for 3366 unique (Fo > 4σF) reflections. There are five distinct Pb2+ cations with coordination numbers from [8] to [11], all of which show stereoactive lone-pair behaviour and which form a strongly bonded cluster of composition [Pb5(OH)5]. There is one Cu+ cation triangularly coordinated by three S2- atoms that belong to three thiosulphate groups, forming a Cu+(S6+O3S2-)3 group. The [Pb5(OH)5] units and [Cu(S2O3)3] groups occur at the vertices of interpenetrating 36 nets to form layers of composition [Pb5(OH)5Cu(S2O3)3] parallel to (010) which are linked by weaker bonds. Examination of the stereochemistry of thiosulphate and thionate structures shows that the combination of and S-S distances are distinct for these two types of structures. © 2009 The Mineralogical Society.

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Cooper, M. A., Hawthorne, F. C., & Moffatt, E. (2009). Steverustite, Pb 2+ 5 (OH) 5 [Cu + (S 6+ O 3 S 2 –) 3 ](H 2 O) 2, a new thiosulphate mineral from the Frongoch Mine Dump, Devils Bridge, Ceredigion, Wal. Mineralogical Magazine, 73(3), 235–250. Retrieved from http://www.scopus.com/inward/record.url?eid=2-s2.0-70249101392&partnerID=tZOtx3y1

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