Raman spectroscopy of natural cordierite at high water pressure up to 5 GPa

Abstract

The high‐pressure behaviour of cordierite, a widespread ring aluminosilicate with channels incorporating fluid compounds (H2O, CO2), is characterized by the absence of phase transitions up to 2.5 GPa. However, the distortion of the ring tetrahedra observed previously at 2.3 GPa is supposed to introduce a phase transition at higher pressure, which has not been checked so far. This work presents a high‐pressure Raman spectroscopic study of natural cordierite compressed in water medium up to 4.7 GPa in a diamond anvil cell. At P > 4 GPa, a disordering of both the framework and intrachannel H2O subsystem is apparent from significant broadening of Raman peaks and the evolution of short‐range order parameters. This is followed by abrupt shifts of the framework and O–H stretching modes at about 4.5 GPa, indicating a first‐order phase transition. Its reversibility is seen from the recovery of the initial spectrum at P < 3 GPa. The shift amplitudes of different framework modes indicate the predominance of distortion over contraction of the framework polyhedra upon this transition. The disordering of the H2O subsystem in the high‐pressure phase is likely a consequence of distortion of the channel‐forming framework elements, which is supposed to be a driving force of this transition. Copyright © 2011 John Wiley & Sons, Ltd.

An X-ray diffraction study of the pressure-induced hydration in cordierite at 4-5 GPa

“…This change of the compression mechanism is apparently related with the transition to a new HP phase associated with PIH in the pressure range between 4.4 and 4.9 GPa. The existence of phase transition is in line with the previous spectroscopic data showing the abrupt shifts of the Raman bands in Z-cordierite in the same pressure interval (Likhacheva et al 2012).…”

“…A significant lowering of the R-factor confirmed the addition of the position Ow2 to be reasonable. It should also be noted that the positional disordering of H 2 O molecules inside the cage due to the appearance of Ow2 agrees with the observed broadening of the intense Raman band of O-H stretching vibrations (Likhacheva et al 2012).…”

“…The cordierite sample (Z-cordierite) used in this study is from the Altai amphibolite complex (Russia), with the chemical formula Na 0.07 (Mg Likhacheva et al (2012). It presents homogenous, inclusion-free, transparent and uniformly colored grains.…”

“…At that point, a significant shrinking of 6mR tetrahedra was observed, which was supposed to introduce a phase transition at higher pressure. Indeed, our recent Raman spectroscopic study has revealed a reversible, low-kinetics phase transition in natural cordierite upon compression in an aqueous medium up to about 4.7 GPa (Likhacheva et al 2012). This transition is evinced by abrupt shifts of all the framework and O-H stretching modes.…”

High-pressure phases of cordierite from single-crystal X-ray diffraction to 15 GPa

“…A major focus has been on how various molecules used as pressure-transmitting media may enter cordierite's channels, modifying the structure's compressibility (e.g., water in pressure-induced hydration) (Mirwald 1982;Mirwald et al 1984;Koepke and Schulz 1986;Likhacheva et al 2011Likhacheva et al , 2013. Recently, Miletich et al (2014a) carried out a high-pressure single-crystal X-ray diffraction study of cordierite in a diamond-anvil cell using a 4:1 methanol-ethanol pressure-transmitting medium.…”