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The high-pressure behavior of synthetic end-member IIb clinochlore, Mg5Al(Si3Al)O10(OH)8, has been studied by synchrotron X-ray powder diffraction to 27 GPa at 300 K. A non-quenchable, reversible transformation occurs between 9 and 10 GPa that is dominated by compression normal to the structural layering and has an associated small but significant shear of the β angle from 97.2 to 96.3°. The high-pressure chlorite is more compressible than the low-pressure phase. Diffraction patterns of the high-pressure chlorite are very similar from 10 to 27 GPa, indicating that it persists stably with no significant change in β to very high pressures: β is effectively locked at the transformation to the high-pressure structure. It is proposed that the transformation is not polytypic and that the distortion reflects reorganization of the interlayer hydrogen bonding, possibly involving novel proton behavior as adjacent sheets of cations of the brucite-like and tetrahedral layers close down on the sheet of interlayer protons. The transformation is likely driven by O atom close-packing requirements imposed by pressure. [ABSTRACT FROM AUTHOR]

Presents a study that examined the effect of pressure on hydrogen bonding in synthetic end-member clinochlore chlorite minerals using Raman spectroscopy. Methodology; Analysis of the Raman frequencies at ambient conditions; Impact of pressure on the Raman frequencies of the samples.

The occurrence, chemical composition and structural characterisation of the new mineral kernowite, ideally Cu2Fe(AsO4)(OH)4⋅4H2O, the Fe3+-analogue of liroconite, Cu2Al(AsO4)(OH)4⋅4H2O, are described. Kernowite (IMA2020-053) occurs on specimens probably sourced from the Wheal Gorland mine, St Day, Cornwall, UK, in the cavities of a quartz-gossan rich in undifferentiated micro-crystalline grey sulfides and poorly crystalline arsenic phases including both pharmacosiderite and olivenite-group minerals. The average composition of kernowite determined from several holotype fragments by electron microprobe analysis is Cu1.88(Fe0.79Al0.09)Σ0.88(As1.12O4)(OH)4⋅3.65H2O. The structure of kernowite has been determined in monoclinic space group I2/a (a non-standard setting of C2/c) by single-crystal X-ray diffraction (SCXRD) to R1 = 0.025, wR2 = 0.051 and Goodness-of-fit = 1.112. Unit-cell parameters from SCXRD are a = 12.9243(4) Å, b = 7.5401(3) Å, c = 10.0271(3) Å, β = 91.267(3)°, V = 976.91(6) Å3 and Z = 4. The chemical formula of this crystal indicated by SCXRD from refined site-scattering is Cu2(Fe3+0.84(1)Al0.16)AsO4(OH)4⋅4H2O. The network of hydrogen bonding has been determined and is similar to that reported for liroconite from Wheal Gorland by Plumhoff et al. (2020). [ABSTRACT FROM AUTHOR]