Multidimensional structural variation in the cyanotrichite family of merotypes: camerolaite-3b-F\bar 1

Abstract

A new superstructure of the mineral camerolaite, CuAl(OH)(HO)[Sb(OH)](SO), has been refined in space group P\bar 1 with unit-cell parameters a = 7.7660 (16), b = 8.759 (4), c = 11.306 (2) Å, α = 108.67 (4), β = 83.41 (3), γ = 126.64 (2)°, V = 581.6 (3) Å and Z = 1, with R = 0.0951 (all data). This is the first refined example of a cyanotrichite-group mineral in which long-range order of interlayer anions produces a superstructure along b, although diffuse scattering has previously been reported that corresponds to short-range order. Though the structure shares with other members of the cyanotrichite group a structural unit in which ribbons of edge-sharing Cu and Al octahedra form layers || (001), the superstructure arises from regular alternation of [SO] and [Sb(OH)] polyhedra along rods that lie between the layers, and phase coupling between rods that maximizes the distance between [SO] groups of adjacent rods along a and c directions. This arrangement suggests an alternative nearly orthogonal choice of unit cell in F\bar 1 with parameters a = 12.473 (26), b = 8.759 (4), c = 21.476 (7) Å, α = 85.94 (4), β = 95.91 (5), γ = 92.34 (9)°, which is recommended for comparing this structural variety of camerolaite with other members of the group.

The crystal structure of Ni-rich gordaite–thérèsemagnanite from Cap Garonne, France

“…The end of the wall includes a large cavity where 5 out of the 14 new species known at Cap Garonne have been found: geminite (Sarp and Perroud, 1990), guarinoite (Sarp, 1993), mahnertite (Sarp, 1996), pushcharovskite (Sarp and Sanz-Gysler, 1997) and thérèsemagnanite (Sarp, 1993). This specimen was collected as part of the systematic study of the mine mineralogy by Association des Amis de la Mine de Cap Garonne (Favreau and Galea-Clolus, 2014; Mills et al ., 2014, 2015, 2017, 2018; Plášil et al ., 2018).…”

Galeaclolusite, [Al6(AsO4)3(OH)9(H2O)4]⋅8H2O, a new bulachite-related mineral from Cap Garonne, France

“…In the course of our ongoing study of the structure and chemistry of minerals from the Cap Garonne copper mine (Favreau and Galea-Clolus, 2014; Grey et al , 2014; Mills et al , 2014, 2015, 2017, 2018, 2019; Plášil et al , 2018), one of us (G.F.) located fibrous coatings of a white mineral for which energy-dispersive X-ray analysis gave the same composition as reported for bulachite (Walenta, 1983). A PXRD pattern for the mineral had a number of sharp peaks in common with those for bulachite, but the pattern did not contain the strongest bulachite peak at 7.78 Å and it contained several broad peaks not present in the Walenta (1983) pattern, with the strongest peak being at d ≈ 10 Å. Electron diffraction (ED) patterns obtained on individual fibres enabled the PXRD pattern to be indexed with a unit cell having the same b and c parameters as bulachite, but with a increased to ~19.9 Å. Thermo-crystallographic studies on the Cap Garonne specimen (Grey et al , 2020b) showed that the PXRD pattern started transforming to that for bulachite at ~50°C and the transformation was complete above 75°C.…”

The crystal structure of ceruleite, CuAl4[AsO4]2(OH)8(H2O)4, from Cap Garonne, France

“…bariopharmacoalumite- Q 2 a 2 b 2 c, Grey et al , 2014) and exceptionally large crystals have been used to help solve the structures of minerals in combination with high-brilliance synchrotron radiation (e.g. cyanotrichite, Mills et al ., 2015; camerolaite, Mills et al ., 2017). Exceptional crystals of the hydrated copper aluminium arsenate ceruleite have been discovered at the mine and, in combination with synchrotron radiation, have been used to elucidate the structure of the mineral first described by Dufet in 1900.…”