Phys Chem Minerals DOI 10.1007/s00269-015-0764-7 ORIGINAL PAPER High-pressure study of azurite Cu3(CO3)2(OH)2 by synchrotron radiation X-ray diffraction and Raman spectroscopy Jingui Xu1,2 · Yunqian Kuang1,2 · Bo Zhang1,2 · Yonggang Liu1 · Dawei Fan1,3 · Wenge Zhou1 · Hongsen Xie1 Received: 21 December 2014 / Accepted: 1 July 2015 © Springer-Verlag Berlin Heidelberg 2015 Abstract The high-pressure properties of natural azurite Keywords Azurite · High pressure · Synchrotron X-ray [Cu3(CO3)2(OH)2] have been investigated by in situ syn- diffraction · Raman spectroscopy · Diamond anvil cell chrotron powder X-ray diffraction and Raman spectroscopy up to 11 and 16 GPa at room temperature, respectively. The results indicate that azurite is stable within the pressure Introduction region in this study. The pressure–volume data from in situ X-ray diffraction experiments were described by a third- Carbonates are the main carbon-bearing phases on the order Birch–Murnaghan equation of state with V 304.5 Earth’s surface, and they can be transported to the Earth’s 0 = (4) Å3, K 40 (2) GPa and K ′ 5.5 (6). The K was mantle along with oceanic lithosphere (Seto et al. 2008). 0 = 0 = 0 obtained as 45.1 (8) GPa when K0′ was fixed at 4. The axial In addition, they are considered to be the potential hosts of compressional behavior of azurite was also fitted with a carbon in the mantle because of the low solubility of car- linearized third-order Birch–Murnaghan equation of state, bon in the silicates of the mantle (Keppler et al. 2003; Das- showing an intense anisotropy with K 29.7 (9) GPa, gupta et al. 2013). The existences of carbonate minerals at a0 = K 25.0 (7) GPa and K 280 (55) GPa. In addition, the mineral inclusions in natural diamonds from the lower b0 = c0 = the Raman spectroscopy of azurite in this study also pre- part of the transition zone and lower mantle (Brenker et al. 2 sents the weak [OH]− group and the rigid [CO3] − group. 2007; Logvinova et al. 2008; Wang et al. 1996) imply that The different high-pressure behaviors of azurite and mala- carbonates (such as magnesite, dolomite and Ba–Sr carbon- chite combined with the smaller isothermal bulk modulus ate) can be stable at the mantle depth. Therefore, studies compared with certain anhydrous carbonates and the obvi- on the behaviors of carbonate minerals at high-temperature ous compression anisotropy of azurite were discussed with and high-pressure conditions are important to understand the experimental results in this study together with the the Earth’s global carbon cycle. The extensive investiga- results from previous studies. Furthermore, the effect of tions of carbonates at extreme conditions are also aroused hydroxyl on the high-pressure behaviors of carbonates was by the fact that the presence of carbon has strong effects on also discussed. the physical and chemical properties of the Earth’s interior (e.g., Gaillard et al. 2008; Dasgupta and Hirschmann 2010; * Dawei Fan Jana and Walker 1997). [email protected] Laboratory studies of carbonate minerals at high pres- sure and high temperature mainly focus on magnesite 1 Key Laboratory of High‑Temperature and High‑Pressure [MgCO ] and calcite [CaCO ] because these are the most Laboratory for High Temperature and High Pressure Study 3 3 of the Earth’s Interior, Institute of Geochemistry, Chinese dominant carbonates in the deep Earth (Oganov et al. Academy of Sciences, Guiyang 550002, China 2006; Gao et al. 2014a). High-pressure and high-temper- 2 University of Chinese Academy of Sciences, Beijing 100049, ature experiments on magnesite [MgCO3] show its stabil- China ity at the depth of the Earth’s lower mantle (Isshiki et al. 3 Center for High Pressure Science and Technology Advanced 2004; Oganov et al. 2008), and thus, it is considered to Research, Changchun 130012, China be a likely host of carbon in Earth’s interior. Differently, 1 3 Phys Chem Minerals calcite [CaCO3] undergoes several pressure-induced phase of azurite can be described with the space group P21, but transitions to aragonite at upper mantle conditions (e.g., this difference has no great influence on lattice parameters Suito et al. 2001). Similar to calcite, dolomite [(Ca, Mg) and atomic fractional coordinates. In the crystal structure CO3] is also not stable with pressure and breaks down of azurite, a triangle is formed by three oxygen ions sur- into a denser magnesite and aragonite [CaCO3] at about rounding one carbon ion; the copper ions are connected to 7 GPa (Martinez et al. 1996; Buob et al. 2006). If minor four oxygen ions forming squares (Fig. 1). There are two Fe is added into structure of dolomite, however, it can be kinds of coordination of the Cu ions: The Cu(1) ions are stable at the pressure and temperature conditions of Earth’s coordinated by O(1) and O(2) ions, whereas the remaining deep mantle (Mao et al. 2011). Additionally, a number of Cu ions (Cu(2)) are coordinated with O(1), O(3) and O(4) high-pressure and high-temperature studies (e.g., Litasov ions (Fig. 1a). Frost et al. (2002), Mattei et al. (2008) and et al. 2013; Boulard et al. 2012) focus on siderite [FeCO3] Buzgar and Apopei (2009) well assigned the Raman bands due to its presence in natural diamond (Stachel et al. of azurite to the corresponding vibrational groups. These 2000), indicating that it is also a candidate of carbon host investigations presented that the Raman spectrum of azur- 2 in the deep Earth. Other carbonate minerals (e.g., PbCO3, ite is composed of three types of modes: [CO3] − groups BaCO3) whose structural phase transitions may occur at (internal modes), [OH]− groups and the Cu–O vibrational more accessible P–T condition ranges are also studied at modes (external or lattice modes). extreme conditions (Ono et al. 2008; Minch et al. 2010a). To date, however, much of our knowledge about azur- The study results of these carbonate minerals can be used ite comes from the studies at ambient conditions, and the to deduce the structural information of the important car- knowledge of the high-pressure properties of hydrous bonates such as magnesite at high pressures. These studied copper carbonates is very limited (Merlini et al. 2012). carbonate minerals include [ZnCO3] (Gao et al. 2014b), Therefore, in the present paper, we investigated the com- rhodochrosite [MnCO3] (Ono 2007a), cerussite [PbCO3] pressional behavior of natural azurite at room temperature (Minch et al. 2010a), witherite [BaCO3] (Townsend et al. and high pressure in a diamond anvil cell, using in situ 2013; Ono 2007b; Chaney et al. 2014) and otavite [CdCO3] angle-dispersive X-ray synchrotron powder diffraction and (Liu and Lin 1997), etc. Raman spectroscopy. The results are then used to probe Although most of the carbonates have been exten- the effect of hydrogen on the behaviors of carbonates at sively investigated at high-pressure and high-temperature extreme conditions. conditions, researches on the effect of hydroxyl on high- pressure properties of carbonates are still limited (Mer- lini et al. 2012). As a kind of hydrous carbonate, azurite Experiments [Cu3(CO3)2(OH)2] can be a proper sample to understand the effect of hydrogen on the behaviors of carbonates at The natural azurite sample was collected from Yunnan extreme conditions. Azurite [Cu3(CO3)2(OH)2] is a hydrous Province, China. The pure azurite mineral grains were copper carbonate and also one of the two basic copper car- selected by hand under a microscope and then ground bonate minerals, the other being malachite [Cu2(OH)2CO3]. under ethanol in an agate mortar for 4–6 h. The ground Generally, azurite has a relationship of intergrowth with samples were examined using the conventional powder malachite [Cu2(OH)2CO3] in the upper oxidized zone of X-ray diffraction method with a D/Max-2200 X-ray dif- copper ore deposits (Anthony et al. 1995). Gattow and fractometer equipped with graphite crystal monochroma- Zemann (1958) first determined the crystal structure of tor and Cu Kα radiation, after being heated at 50 °C in a azurite, and whereafter the crystal structure of azurite was constant temperature furnace for 2 h. The ambient X-ray refined by Zigan and Schuster (1972) using single-crystal spectrum of azurite was indexed according to the standard neutron diffraction data as well as Belokoneva et al. (2001) spectra (JCPDS72-1270), confirming that the structure of with single-crystal X-ray diffraction data. Anhydrous car- the natural azurite mineral was monoclinic and belongs to bonates can be classified into three types based on their the P21/c space group. structure differences: calcite group, aragonite group and In situ high-pressure angle-dispersive X-ray diffrac- dolomite group (Klein et al. 1993). Calcite group is trigonal tion experiments were performed at the BL15U1 beam- with space group R3c, aragonite group has orthorhombic line, Shanghai Synchrotron Radiation Facility (SSRF) and structures (Pmcn), and dolomite group is also trigonal like 4W2 beamline of Beijing Synchrotron Radiation Facility calcite group but with lower symmetry (R3). Unlike anhy- (BSRF). The incident synchrotron X-ray beam was mon- drous carbonates, azurite belongs to monoclinic crystal sys- ochromatic with a wavelength of 0.6199 Å. A symmetric tem, and its space group is P21/c. Lately, Rule et al. (2011) diamond anvil cell (DAC) equipped with two diamonds presented their single-crystal neutron diffraction results of anvils (500-μm-diameter culet) and tungsten carbide sup- azurite, drawing the conclusion that the crystal structure ports was used to generate the high pressure. A rhenium 1 3 Phys Chem Minerals Fig.