Vibrational Investigation of Pressure-Induced Phase Transitions of Hydroxycarbonate Malachite Cu2(CO3)(OH)2

Abstract

Malachite Cu2(CO3)(OH)2 is a common hydroxycarbonate that contains about 15.3 wt % H2O. Its structural chemistry sheds light on other hydroxyl minerals that play a role in the water recycling of our planet. Here using Raman and infrared spectroscopy measurements, we studied the vibrational characteristics and structural evolution of malachite in a diamond anvil cell at room temperature (25 °C) up to ~29 GPa. Three types of vibrations were analyzed including Cu–O vibrations (300–600 cm−1), [CO3]2− vibrations (700–1600 cm−1), and O–H stretches (3200–3500 cm−1). We present novel observations of mode discontinuities at pressures of ~7, ~15, and ~23 GPa, suggesting three phase transitions, respectively. First, pressure has a great effect on the degree of deformation of the [CuO6] octahedron, as is manifested by the various shifting slopes of the Cu–O modes. [CuO6] deformation results in a rotation of the structural unit and accordingly a phase transition at ~7 GPa. Upon compression to ~15 GPa, the O–H bands redshift progressively with significant broadness, indicative of an enhancement of the hydrogen bonding, a shortening of the O···O distance, and possibly somewhat of a desymmetrization of the O–H···O bond. O–H mode hardening is identified above ~15 GPa coupled with a growth in the amplitude of the lower-energy bands. These observations can be interpreted as some reorientation or reordering of the hydrogen bonding. A further increment of pressure leads to a change in the overall compression mechanism of the structure at ~23 GPa, which is characterized by the blueshift of the O–H stretches and the softening of the O–C–O in-plane bending bands. The hydrogen bonding weakens due to a substantial enhancement of the Cu–H repulsion effect, and the O···O bond length shows no further shortening. In addition, the change in the local geometry of hydrogen is also induced by the softening of the [CO3]2− units. In this regard we may expect malachite and other analogous hydroxyl minerals as capable of transporting water downward towards the Earth’s transition zone (~23 GPa). Our results furnish our knowledge on the chemistry of hydrogen bonding at mantle conditions and open a new window in understanding the synergistic relations of water and carbon recycling in the deep Earth.

High-pressure and high-temperature vibrational properties and anharmonicity of carbonate minerals up to 6 GPa and 500 °C by Raman spectroscopy

“…DOI: https://doi.org/10.2138/am-2020-7404. http://www.minsocam.org/ (Shahar et al 2005), magnesite (Williams et al 1992;Gillet 1993;Gillet et al 1993;Spivak et al 2014;Müller et al 2017;Farsang et al 2018;Liang et al 2018a), malachite (Gao and Yuan 2020), nyerereite (Rashchenko et al 2017), otavite (Minch et al 2010a), rhodochrosite (Farfan et al 2013;Liu et al 2016;Farsang et al 2018;Zhao et al 2018), shortite (Borodina et al 2018;, siderite (Farfan et al 2012;Lin et al 2012;Spivak et al 2014;Cerantola et al 2015;Müller et al 2016Müller et al , 2017Farsang et al 2018;Liang et al 2018b), spherocobaltite (Chariton et al 2018), strontianite Liu 1997c, 1997b;Biedermann et al 2017a;Efthimiopoulos et al 2019), and witherite Liu 1997a, 1997b;Chaney et al 2015). Highpressure and high-temperature vibrational data have been previously combined to estimate anharmonicity and calculate thermodynamic properties of certain carbonates (Matas et al 2000;Wang et al 2019b).…”

Surface-Functionalized Magnetic Silica-Malachite Tricomposite (Fe–M–Si tricomposite): A Promising Adsorbent for the Removal of Cypermethrin

“…The addition of SiO 2 and TiO 2 can have a positive impact on the adsorption capacity and efficiency of Fe 3 O 4 /malachite (M) for removing contaminants from water or soil. SiO 2 can improve the stability and reusability of the adsorbent, making it more practical for large-scale applications. ,,,− …”

Re-examination of vesbine in vanadate-rich sublimate-related associations of Vesuvius (Italy): mineralogical features and origin

“…for bands assignments: Vbo: Brown and Ross, 1972;Busca et al, 1994;Frost et al, 2011;Chukanov, 2014;Arvind et al, 2016;Bayat et al, 2018;Ccl: Chukhrov et al,1969;Frost and Xi, 2013;Chukanov, 2014. Mlc/Azu: Goldsmith andRoss, 1968;Schmidt and Lutz, 1993;Frost et al, 2002b;Stoilova et al, 2002;Chukanov, 2014;Gao and Yuan, 2020;Ata: Frost et al, 2002a;Martens et al, 2003;Tao et al, 2011;Chukanov, 2014. Blk: Liu et al, 2011Chukanov, 2014;Zhao et al, 2020.…”