We present Raman data for camerolaite, cyanotrichite and carbonatecyanotrichite, and using synchrotron single-crystal X-ray diffraction have solved the structure of camerolaite from the Tistoulet Mine, Padern, Aude Department, France. Camerolaite crystallizes in space group P1 with the unit-cell parameters: a = 6.3310(13) Å, b = 2.9130(6) Å, c = 10.727(2) Å, α = 93.77(3)°, β = 96.34(3)°, γ =79.03(3)º, V = 192.82(7) Å3 and Z = ⅓, with respect to the ideal formula from the refinement, Cu6Al3(OH)18(H2O)2[Sb(OH)6](SO4). The crystal structure was solved to R1 = 0.0890 for all 1875 observed reflections [Fo > 4σFo] and 0.0946 for all 2019 unique reflections. The P cell has been transformed into a C-centred cell that aids comparison with that of the structurally related khaidarkanite by aC = 2aP – bP, giving parameters a = 12.441(3), b = 2.9130(6), c = 10.727(2) Å, α = 93.77(3), β = 95.57(3), γ = 92.32(3)º and Z = ⅔ in C1. Edge-sharing octahedral ribbons Cu2Al(O,OH,H2O)8 form hydrogen-bonded layers || (001), as in khaidarkanite. The partially occupied interlayer Sb and S sites of the average structure are in octahedral and tetrahedral coordination by oxygen, respectively. They cannot be occupied simultaneously, which leads to regular alternation of [Sb(OH)6]– and SO42– groups in rods || y, resulting in local tripling of the periodicity along y for the Sb(OH)6–SO4 rods. Thus, camerolaite has a ‘host–guest’ structure in which an invariant host module (layers of Cu–Al ribbons) has embedded rod-like guest modules with a longer periodicity. Coupling between the phases of these rods is only short-range, resulting in diffuse X-ray scattering rather than sharp superstructure reflections. Similar disorder is known for parnauite, and is deduced for other members of the cyanotrichite group (cyanotrichite, carbonatecyanotrichite and khaidarkanite). Group members all share the Cu–Al ribbon module but have interlayer rods of different compositions and topologies; thus, they form a merotypic family. The low symmetry of the camerolaite average structure suggests other possibilities for structure variation in the group, which are discussed.

In 1997 and 1998, several samples from the El Guanaco Mine, near Taltal, Chile, were submitted for analysis by G. Färber (Samswegen, Germany) and G. Backmann (Dresden, Germany) to one of the authors (T.W.). Semiquantitative EDX analyses and X-ray powder diffraction studies showed that the material is different from any known mineral or synthetic compound. Subsequent investigations, which included a crystal-structure determination, confirmed that the mineral is a new species. The mineral

The crystal structures of the 3R polytypes of takovite and woodallite are presented. The structure of takovite was solved on a single crystal from the Agoudal mine, Bou Azzer district, Tazenakht, Morocco to R 1 = 1.87 % for 94 unique reflec-

The acicular blue minerals of the cyanotrichite group have been known for more than two centuries. However, their crystals are usually very thin, deformed and mosaiced, so their structural and chemical complexities are only just being elucidated, thanks to synchrotron XRD from micron-scale regions of good crystal quality.Structures in the cyanotrichite group share a [Cu2Al(OH)6]+ ribbon of edge-sharing Cu and Al polyhedra || b of a (pseudo)monoclinic subcell. The ribbons lie en echelon in layers || (001), while between these layers, SO42-tetrahedra, [AlF4 ( The average cyanotrichite structure has b ~ 2.9 Å, defined by the width of one (Cu,Al)X6 octahedron along a ribbon. However, the structure is an intergrowth of an invariant 'host' module (layers of Cu-Al ribbons) with rod-like 'guest' modules whose periodicity is necessarily a multiple of that of the host. Thus, rods may be offset relative to their neighbours in a variety of ways. Coupling between the rods is usually short-range, resulting in diffuse X-ray scattering only. The first structure refined was that of khaidarkanite [1]. Although the periodicity along any given fluoraluminate rod must be 4b [2], the structure showed no long-range order, and the unit cell (C2/m, a = 12.326 Å, b = 2.907 Å, c = 10.369 Å, β = 97.90º) is typical of the average structure for the group. Loss of C-centering in some specimens and a wide range of β angles 92-99º [1], suggested that structural variation occurs without significant change in cell dimensions, due to (i) offset of ribbons || b in the xy plane; (ii) offset of layers || a in the xy plane; and (iii) shear of ribbons in the xz plane. Symmetry-lowering distortions were characterised in refinements of the triclinic C-1 structure of a camerolaite crystal [2] and of the P2/m structure of one of the two cyanotrichite crystals refined in [3] (the other was C2/m).Crystals of both cyanotrichite and camerolaite from the Cap Garonne mine (France) gave sharp superstructure reflections. In the case of P2/m cyanotrichite, a 4b superstructure was observed, consistent with the sequence of species [-SO4-SO4-(H2O)2-(H2O)2-] along any given rod, but the data was not good enough to refine. However, a single crystal of camerolaite has yielded superstructure peaks sharp enough for refinement, confirming that the 3b superstructure arises from alternation of Sb(OH)6 and SO4 along b. For the first time, we observe a large systematic offset from one Sb to the next along the c direction (~0.4b), which means that the most nearly orthogonal cell is actually F-centred triclinic with a doubled c repeat and doubled volume (F-1, a = 12.472 Å, b = 8.758 = 3 × 2.919 Å, c = 21.478 = 2 × 10.739 Å, α = 85.93º, β = 95.90º, γ = 92.35º).

The crystal structure of a specimen of `Pb-rich' chabournéite from Jas Roux, Hautes-Alpes, France, with the chemical formula obtained by electron microprobe analysis of Ag(0.04 (1))Tl(2.15 (2))Pb(0.64 (1))Sb(5.12 (1))As(5.05 (1))S(17.32 (5)), has been solved by X-ray single-crystal diffraction on the basis of 36,550 observed reflections (with F(o) > 4σF(o)) with a final R1 = 0.074. Pb-rich chabournéite is triclinic P1, with unit-cell parameters a = 8.5197 (4), b = 42.461 (2), c = 16.293 (8) Å, α = 83.351 (2), β = 90.958 (2), γ = 84.275 (2)°, V = 5823 (3) Å(3). Its structural formula is close to [Tl2(Pb(0.8)Tl(0.1)Sb(1.1))](Sb(4.1)As(4.9))S17, with Z = 8. Its crystal structure is formed by the alternation of two pairs of slabs along the b axis, deriving from the SnS and PbS archetypes, respectively. 104 independent cation sites and 136 S sites occur in the unit cell. Slab interfaces show the alternation, along c, of Tl sites, ninefold coordinated, with Pb, Sb or mixed/split (Pb,Sb) and (Pb,Tl) sites. Within the slabs, 72 independent M(3+) sites (M(3+) = As, Sb) occur. Considering M(3+)-S bond distances shorter than 2.70 Å, MS3 triangular pyramidal groups are condensed according to various M(m)S(n) chain fragments (`polymers'). The solution of the crystal structure of chabournéite allows its comparison with the closely related homeotypes protochabournéite and dalnegroite.