The Crystal Structure and Gibbs Free Energy of Formation of Chukanovite As T an Oxidation Product of Carbon Steel in Human Liver ⁎ Seungyeol Lee, Huifang Xu

Chemical Geology 488 (2018) 180–188

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Chemical Geology

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The crystal structure and Gibbs free energy of formation of chukanovite as T an oxidation product of carbon steel in human liver ⁎ Seungyeol Lee, Huifang Xu

NASA Astrobiology Institute, Department of Geoscience, University of Wisconsin–Madison, Madison, WI 53706, United States

ARTICLE INFO ABSTRACT

Editor: Dong Hailiang Chukanovite has been identified as an oxidation product of carbon steel in a human liver through powder X-ray ff Keywords: powder di raction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Chukanovite Steel oxidation products include siderite, chukanovite, vivianite, magnetite, goethite, 2-line ferrihydrite. Human liver Hydroxylapatite and amorphous silica surrounding the oxidized steel are precipitated from body fluid. The

Steel corrosion Rietveld refinement of the chukanovite structure shows it is as expected monoclinic, space group of P21/a, with Gibbs free energy a = 12.402(2), b = 9.414(1), c = 3.216(1) Å, β = 97.73(3)°. The standard Gibbs free energy of formation of − Medical mineralogy chukanovite is estimated at −1167.2 ± 1.2 kJ mol 1 from the equilibrium between siderite and chukanovite. By using linear free energy relationship, the Gibbs free energy of formation for other isostructural phases of pokrovskite, parádsasvárite, and nullaginite are predicted. The results of this study could improve the mineralogical and geochemical properties of chukanovite which is an oxidation product of carbon steel relevant also in radioactive waste containers and oil/gas pipes. Furthermore, the combined method of experimental measurements and geochemical modeling could be a useful tool to study the formation of inorganic solid precipitates and bio-materials in biofluids, and is especially important in medical mineralogy field.

1. Introduction firstly determined through X-ray synchrotron diffraction data by Pekov et al. (2007), and subsequently refined through electron diffraction data Chukanovite was described as a new mineral by Pekov et al. (2007), by Pignatelli et al. (2014). The standard Gibbs free energy of formation occurring as a terrestrial alteration product of the Dronino iron me- of chukanovite was also reported in several studies (Nishimura and teorite. Chukanovite is an iron hydroxide‑carbonate mineral “Fe2(CO3) Dong, 2009; Lee and Wilkin, 2010; Azoulay et al., 2012; Kim et al., (OH)2” which is isostructural with the malachite-rosasite group, with 2017). However, their equilibrium condition and the Gibbs free energy 2+ general formula Me2 (CO3)(OH)2. Several studies reported chukano- differ from each other due to their different experimental conditions or vite as a metastable corrosion product of carbon steels (Peev et al., experimental errors. In this study, we provide a crystal structure re- 2001; Lee and Wilkin, 2010; Azoulay et al., 2014; Pandarinathan et al., finement and Gibbs free energy of formation of chukanovite formed in 2014). Recently, the formation of chukanovite has been recognized as an oxidized steel that interacted with body fluid in human liver. In an important oxidation product of long-term corrosion in oil/gas pi- addition, we predict the standard Gibbs free energy of formation of peline steels (Ko et al., 2014) and nuclear waste disposal (Hill et al., chukanovite and other isostructural minerals (malachite-rosasite group) 2015). Chukanovite was also observed in corrosion layers of iron ar- using the Sverjensky-Molling equation (Sverjensky and Molling, 1992). chaeological artifacts (Saheb et al., 2008; Remazeilles et al., 2009) and The new results will help us to better understand the mineralogical and zerovalent iron permeable reactive barriers (Lee and Wilkin, 2010). geochemical characteristics of chukanovite and associated minerals. Biogenic chukanovite was reported as a microbial reduction product of Fe2+-excess magnetite (Kukkadapu et al., 2005). 2. Sample and methods There are not many structural reports and thermodynamic data for chukanovite, because it is generally precipitated as a microcrystalline 2.1. Oxidized carbon steel in human liver phase mixed together with other iron minerals (e.g. siderite and goethite) (Nishimura and Dong, 2009; Azoulay et al., 2014; Ko et al., 2014; The sample is a surgery product from a middle-aged man's liver. The Pandarinathan et al., 2014). The crystal structure of chukanovite was steel was discovered as an unusual magnetic material in the patient's

⁎ Corresponding author at: Department of Geoscience, University of Wisconsin–Madison, 1215 West Dayton Street, A352 Weeks Hall, Madison, WI 53706, United States. E-mail address: [email protected] (H. Xu). https://doi.org/10.1016/j.chemgeo.2018.04.033 Received 26 January 2018; Received in revised form 24 April 2018; Accepted 30 April 2018 Available online 05 May 2018 0009-2541/ © 2018 Published by Elsevier B.V. S. Lee, H. Xu Chemical Geology 488 (2018) 180–188

Fig. 1. Optical images of the oxidized steel sample. The metallic steel is coated with dark brown iron minerals and white fiber-like hydroxylapatite. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) liver during a pre-NMR magnetic check. The steel sample about 2.4. Transmission electron microscopy (TEM) 6.1 × 3.8 × 1.8 mm (Fig. 1) was oxidized in the liver over the years. The metallic steel is coated with dark brown oxidized iron minerals and TEM samples were prepared by dropping suspensions of crushed fiber-like hydroxylapatite (outermost) (Fig. 1). The carbon steel had samples onto lacy‑carbon-coated 200-mesh Cu grids. TEM imaging and derived from outside of the body, however, we don't know exactly selected-area electron diffraction (SAED) analysis were carried out where the sample originated from. It could be a broken part of drill bit using a Philips CM200-UT microscope operated at 200 kV in the due to its strength and hardness. Materials Science Center at the University of Wisconsin-Madison. The chemical composition was obtained using TEM-EDS system equipped with a Li-drifted Si detector (Oxford instruments Link ISIS). An electron 2.2. X-ray powder diffraction (XRD) beam diameter of ~50 nm was used for collecting X-ray EDS spectra. We scratched and separated the particles from the core to the outermost zones and then divided into the magnetic and nonmagnetic 2.5. pH-Eh diagram zones. We acquired the XRD results of powdered samples placed inside polyimide tube (1 mm diameter). XRD patterns were recorded on a 2-D Geochemist's Workbench 11 (Rockware Inc., Golden, CO, USA) image-plate detector using a Rigaku Rapid II instrument (Mo-Kα ra- software package was used to construct Eh-pH diagrams. Body fluid diation) in the Geoscience Department at the University of Wisconsin- compositions (Na+ = 142 mM, K+ = 5 mM, Mg2+ = 1.5 mM, 2+ − – 2− Madison. Two-dimensional diffraction patterns were converted to Ca = 2.5 mM, Cl = 148.8 mM, HCO3 = 27 mM, HPO4 = 1 mM, 2− conventional 2θ vs. intensity patterns using Rigaku's 2DP software. and SO4 = 0.5 mM) were used for modeling equilibrium reactions at Synthetic silicon powder was used as the standard for calibration of 37 °C (Bigi et al., 2005; Waugh and Grant, 2010). The potential surface −4 – −2 2− −6 diffraction line positions. Data were collected between 5 and 40° 2θ water condition (Fe = 10 M, HCO3 =10 M, HPO4 =10 M) range in a spin mode with exposure time of 15 min per pattern. were used for modeling equilibrium reactions at 25 °C (Lee and Wilkin, − For Rietveld refinement, the pure chukanovite was separated from 2010). The total dissolved iron (ΣFe) is estimated to be 10 4 M based the nonmagnetic middle zone. The Rietveld refinement analysis was on mineral assemblage from XRD analysis. All calculations were con- performed with TOPAS 5 software (Bruker, MA, USA) to determine the ducted with the thermos database that includes new chukanovite data detailed crystal structure of chukanovite and quantitative analysis of from this study. oxidized iron minerals in the sample. We used previous chukanovite model (Pekov et al., 2007) as the initial structure with Fe (CO )(OH) 2 3 2 3. Results chemical formula based on TEM-EDS analysis (Supplementary Fig. S1). The space group of P2 /a setting of chukanovite in the Rietveld re- 1 3.1. XRD finement is in good agreement with isostructural malachite-rosasite group minerals. A pseudo-Voigt function was used for fitting the peak Four distinct zones can be recognized in the studied sample, namely profiles. a core zone, two magnetic middle zones, two nonmagnetic middle zones and two outmost zones. X-ray diffraction results from the selected 2.3. Scanning electron microscope (SEM) zones suggest that the oxidized sample is composed of solid iron, siderite, chukanovite, vivianite, magnetite, goethite, and hydro- Samples for SEM analysis were put on glass slides, coated with xyapatite (Fig. 2). The XRD pattern of core zone shows that the initial carbon (~100 Å). To prevent the oxidation reaction, air exposure was material is zero-valent metallic iron (Figs. 1c and 2). The chukanovite minimized during the sample preparation. All SEM images were ob- coexists with the siderite and goethite phase in the sample (Fig. 2). The tained using a Hitachi S3400N variable pressure microscope with an X- magnetic phase of the middle zone is magnetite (Fig. 2). The outermost ray energy-dispersive spectroscopy (EDS) attachment. High-resolution zones consist of poorly crystallized goethite and hydroxylapatite Ge detector and imaging was used in backscattered electron image (Fig. 2). The goethite is the final oxidation product of carbon steel mode to study morphology and chemical variations. (Fig. 2). The concentration of goethite increased from the core to the

181 S. Lee, H. Xu Chemical Geology 488 (2018) 180–188

Fig. 2. Powder X-ray diffraction patterns of oxidized steel sample from the core to outmost zone. Percentages of mineral phases were calculated using Rietveld refinement method. Diffraction peaks of reference minerals are also illustrated at the bottom. Hap: Hydroxylapatite, G: Goethite, M: Magnetite, C: Chukanovite, V: Vivianite, S: Siderite, and Fe: Iron. outer zones, indicating the oxidization process of the carbon steel under occur in the form of acicular clusters on the surface of the sample. The human body fluid condition (Fig. 2). hydroxylapatite of the outmost part is associated with amorphous silica (Fig. 3c). The BSE image of core part shows that the carbon steel is covered with the mixture of siderite and chukanovite (Fig. 3d). X-ray 3.2. SEM EDS spectrum from the steel shows Si and Fe peaks (Fig. 3f). The carbon steel contains ~2 wt% silicon that helps to improve the strength and The backscattered electron (BSE) image shows twinning of magne- hardness of steel (Abramowitz and Moll, 1970). Identifying individual tite crystals (Fig. 3a). Fig. 3b shows that micro-sized goethite crystals

182 S. Lee, H. Xu Chemical Geology 488 (2018) 180–188

Fig. 3. The BSE images and EDS spectra of oxidized steel sample: (a) magnetite, (b) goethite, (c) hydroxylapatite coexisted with amorphous silica, (d-f) carbon‑silicon steel covered by siderite and chukanovite. grains using the SEM is difficult because the iron oxidized products are amorphous silica in the sample using XRD, SEM, and TEM (Figs. 2-4). microcrystalline mixtures. The mineral assemblages indicate the iron oxidation reaction of carbon steel (Fe0 → Fe2+ → Fe3+)(Fig. 2). Several studies reported that side- 3.3. TEM rite and chukanovite are early oxidation products of carbon steel in CO2-bearing aqueous solutions (Remazeilles et al., 2009; Azoulay et al., The combination of TEM images with SAED patterns and EDS 2014; Leon et al., 2014; Pandarinathan et al., 2014). The steel, when spectra can help us to identify the individual minerals in the sample interacted with phosphate, can also produce the vivianite phase under (Fig. 4 and Supplementary Fig. S1). We observed the chukanovite, neutral pH conditions (Bryant and Laishley, 1993). Goethite and mag- siderite, vivianite, magnetite, goethite, and 2-line ferrihydrite from iron netite are relatively long-term oxidation product of carbon steel (Marco oxidation products using the TEM instrument (Fig. 4). The bright-field et al., 2000; Asami and Kikuchi, 2003; de la Fuente et al., 2011). Some TEM images of chukanovite commonly show (010) and (021) faces studies reported ferrihydrite nanoparticles as a corrosion product of (Fig. 4a). The (021) plane is the cleavage plane of chukanovite. Siderite steel (Marco et al., 2000; Dodge et al., 2002). However, another pos- and magnetite show irregular shapes, while the vivianite shows blade- sibility is that the 2-line ferrihydrite can be precipitated from the iron fl like morphology (Fig. 4b–d). Goethite (Pmnb setting) crystals elongated component in body uid. The ferrihydrite is a main component of along the [100] direction (Fig. 4e). The 7.43 Å of diffraction spots may ferritin that is produced by all living organisms (Cowley et al., 2000). be related to triple chains of iron octahedra (Fig. 4e). Some nano-sized Hydroxyapatite is a main inorganic component of bone and calcified goethite crystals show diffuse streaks with very weak (020) and (040) tissues precipitated from body fluid (Weng et al., 1997; Rhee and diffractions in SAED pattern, which indicates disordered structure or Tanaka, 1999). The amorphous silica can be also formed from the hy- the presence of a proto-goethite like phase (Lee et al., 2016)(Fig. 4f). drous silica component in body fluid where the silica acts as nucleation Aggregates of 2-line ferrihydrite showing only two diffuse diffraction sites for hydroxylapatite precipitation (Li et al., 1992; Tas, 2000) rings at ~2.5 Å and ~1.5 Å in the SAED pattern were also observed in (Fig. 3c). the outer zone (Fig. 4g). The Si peak is detected in the TEM-EDS spectrum of 2-line ferrihydrite (Supplementary Fig. S1). The silicon 4.2. Crystal structure of chukanovite peak may be related to the SiO4 tetrahedra adsorbed on the 2-line fl ferrihydrite surface during the reactions in the body uids. The chukanovite is the ferrous iron end-member of the rosasite- malachite group. The crystal structure of chukanovite consists of rib- 4. Discussions bons of edge-sharing octahedra along the c-axis (Fig. 5). The ribbons are linked together through corner-sharing that are interconnected through 4.1. Mineralogy of the oxidized carbon steel in human liver carbonate groups (Fig. 5). The Fe1 is coordinated by four oxygen atoms and two hydroxyls, whereas, the Fe2 is coordinated by four hydroxyls We observed zero-valent metallic iron, siderite, chukanovite, vi- and two oxygen atoms (Fig. 5). vianite, magnetite, goethite, 2-line ferrihydrite, hydroxylapatite, and A powder XRD pattern of pure chukanovite collected from the

183 S. Lee, H. Xu Chemical Geology 488 (2018) 180–188

Fig. 4. The bright-field TEM images of the oxidation products from the carbon-steel: (a) chukanovite, (b) siderite, (c) vivianite, (d) magnetite, (e) goethite, (f) disordered goethite, and (g) 2-line ferrihydrite. nonmagnetic middle zone is shown in Fig. 6. Rietveld refinement was chukanovite coexists with siderite in the sample under long-term performed to refine the crystal structure of chukanovite (Fig. 6). The equilibrium condition (several years), which is in good agreement with

Fe2(CO3)(OH)2 chemical formula was used for the structure reﬁnement, previous studies at neutral pH conditions (Nishimura, 2009; Ko et al., which is based on the TEM-EDS spectrum of chukanovite (Supple- 2014; Pandarinathan et al., 2014; Azoulay et al., 2015). In case of high mentary Fig. S1). The reﬁned unit cell parameters of chukanovite are: pH conditions (10.3–10.9), chukanovite can be formed with Fe(II) hy- a = 12.402(2), b = 9.414(1), c = 3.216(1) Å, and β = 97.73(3)° with droxide without siderite phase in carbonate suspensions (Azoulay et al.,

Rwp = 7.33%. The unit cell parameters are listed in Table. 1, together 2012). The equilibrium reaction between chukanovite Fe2CO3(OH)2 with previously reported chukanovite structures (Pekov et al., 2007; and siderite (FeCO3) can be written as: Pignatelli et al., 2014; Perchiazzi et al., 2017) and other isostructural −+ minerals in the rosasite-malachite group (Zigan et al., 1977; Perchiazzi, Fe23 CO (OH) 2++=+ HCO 3 H 2FeCO3 2H 2 O. 2006; Perchiazzi and Merlino, 2006; Perchiazzi et al., 2017). The re- And then, we can obtain the following relationship in equilibrium fi ned atomic coordinates of chukanovite are listed in Table 2. The re- conditions. sults of structure refinement agree with those reported before (Pekov °− et al., 2007). Our unit cell parameters are slightly larger than those pH=− ΔG /2.303RT+ log[HCO3 ]. from the chukanovite in the meteorite (Table 1). Small amount of ferric From the equation, the equilibrium condition depends on the tem- iron reported in the natural chukanovite (Pekov et al., 2007) could be a – reason for its smaller unit cell. perature, pH and the activity of HCO3 in solution. The normal body The refined bond distances, polyhedral volumes, and bond length temperature is ~37 °C and blood pH is regulated to stay within the distortions of chukanovite are compared with previously reported narrow range of 7.35 to 7.45 (Waugh and Grant, 2010). The activity – – chukanovite structures (Pekov et al., 2007; Pignatelli et al., 2014) and range of HCO3 is 21 27 mM in normal blood conditions (Waugh and Grant, 2010). The ΔG° represents the Gibbs free energy of the above rosasite mineral from Ojuela mine, Mexico (Perchiazzi, 2006)(Table. − 3). All the data suggest that the Fe1 octahedron is larger and more reaction. The standard state Gibbs free energies of HCO3 , siderite, and − − − −1 distorted than the Fe2 octahedron, which is similar to the other mala- H2O(l) for the calculation are 568.8, 666.7, and 237.8 kJ mol , chite/rosasite group minerals (Table. 3)(Zigan et al., 1977; Perchiazzi, respectively (Benjamin, 2014). After considering all the factors including temperature, the standard Gibbs free energy of formation (ΔG°f) 2006; Perchiazzi and Merlino, 2006). Density-functional theory (DFT) − of chukanovite is estimated at −1167.2 ± 1.2 kJ mol 1. The un- calculations suggest that the distortion of octahedron may be associated – with the proton substitution (Chaka, 2016). The distortion of the car- certainty is from the range of pH and the activity of HCO3 in body fl bonate group in the refined chukanovite structure is minor from its uid. There are several reported values for the standard Gibbs free energy regular triangular geometry (Table 3). − of formation of chukanovite: −1169.3 kJ mol 1 (Nishimura and Dong, − 2009); −1171.5 ± 3.0 kJ mol 1(Azoulay et al., 2012), −1 4.3. Gibbs free energy of chukanovite and − 1174.4 ± 6 kJ mol (Lee and Wilkin, 2010). Our ΔG°f value is analogous to the value of Nishimura and Dong (2009) that calculated The results of XRD and SEM analysis (Figs. 2 and 3) show that from the same equilibrium condition between siderite and chukanovite.

184 S. Lee, H. Xu Chemical Geology 488 (2018) 180–188

Fig. 5. (a) Chukanovite structure showing the edge-sharing octahedra ribbons projected along slightly tiled c-axis. (b) Bond distances for the polyhedral of chukanovite. The Fe, C, O, and OH are colored in brown, gray, red and blue, respectively. (For interpretation of the references to color in this ﬁgure legend, the reader is referred to the web version of this article.)

Azoulay et al. (2012) used another equilibrium reaction between chu- conditions and experimental errors of previous experiments, our cal- kanovite and Fe(OH)2 because their experiment could not observe the culated ΔG°f value of chukanovite should be the right one. mixtures of siderite and chukanovite due to the high pH condition. Lee The linear free energy relationship is a useful method to predict the and Wilkin (2010) proposeda Gibbs free energy of formation for chu- thermodynamic energies of isostructural minerals for which no ex- kanovite from the equilibrium between chukanovite and dissolved perimental data are available (Sverjensky and Molling, 1992; Xu and 2+ − species in solution (Fe and HCO3 ). The value may be a little bit too Wang, 1999, 2017; Wang and Xu, 2001). For the isostructural family of low because their chukanovite dissolution might not reach equilibrium. the malachite-rosasite group, the Gibbs free energy of formation has The range of pH values of our condition is 7.35–7.45 that followed by been reported only for two phases (chukanovite and malachite). By normal body ﬂuid condition, which is lower than other three experi- using the Sverjensky-Molling equation combined with ionic radii, sol- ments i.e., pH 8.26–10.91. Considering the impurities, equilibrium vation energies, and Gibbs free energy of formation of divalent cations

185 S. Lee, H. Xu Chemical Geology 488 (2018) 180–188

Table 2 Atomic coordinates of chukanovite.

Atom x y z Uiso

Fe1 0.2109(5) 0.0009(1) 0.9588(5) 0.075(9) Fe2 0.3949(5) 0.7688(3) 0.5651(3) 0.075(9) C 0.1436(7) 0.7331(5) 0.4935(4) 0.217(16) O1 0.1401(3) 0.8644(5) 0.3691(6) 0.081(8) O2 0.2342(2) 0.6671(5) 0.5479(5) 0.081(8) O3 0.0539(2) 0.6715(6) 0.5552(7) 0.081(8) OH4 0.3794(8) 0.8997(5) 0.0576(5) 0.063(7) OH5 0.4266(5) 0.6181(7) 0.1327(3) 0.063(7)

Lattice parameters: a = 12.402(2) Å, b = 9.414(1) Å, c = 3.216(1) Å, β = 97.73(3)°.

Table 3 Bond distances (Å), polyhedral volume and distortion index of three chukano- Fig. 6. Rietveld refinement of XRD pattern of chukanovite. Experimental pat- vite structure and rosasite structure. tern in blue, calculated pattern in red, difference line in gray. (For interpretation of the references to color in this figure legend, the reader is referred to the Chukanovite (1) (2) (3) Rosasite (6) web version of this article.) Fe1 O1 2.115(5) 2.07(3) 2.18(2) Cu1 O1 2.078(8) O1 2.360(4) 2.41(2) 2.20(2) O1 2.443(7) (Sverjensky and Molling, 1992; Sverjensky, 1992; Xu et al., 2017a), the O2 2.267(4) 2.23(2) 2.32(2) O2 2.057(5) Gibbs free energies of formation of other isostructural minerals can be O2 2.422(5) 2.47(3) 2.36(2) O2 2.519(3) predicted from a linear free energy relationship (Supplementary Table OH4 2.280(11) 2.26(2) 2.03(2) OH4 1.952(9) OH5 2.019(9) 2.04(2) 2.07(2) OH5 1.89(1) S1). The calculated Gibbs free energies of formations for pokrovskite, Volume (Å3) 14.892(6) 14.952 13.850 13.090 −1 parádsasvárite, and nullaginite are −1860.0 kJ mol , Distortion 0.0525 0.0595 0.0449 0.0998 − − −1275.5 kJ mol 1, and −1081.1 kJ mol 1, respectively, based on the Fe2 O2 2.205(7) 2.24(2) 2.21(2) Zn2 O2 2.256(3) linear free energy relationship and a previously reported value for O3 2.055(7) 2.02(3) 2.12(3) O3 2.046(3) malachite (Stella and Ganzerli-Valentini, 1979) (Supplementary Table OH4 2.033(4) 2.01(2) 2.13(2) OH4 2.01(1) S1). OH4 2.036(5) 2.09(2) 2.17(2) OH4 2.16(1) Based on the thermodynamic data of chukanovite, two Eh-pH dia- OH5 2.304(5) 2.31(3) 2.14(2) OH5 2.07(1) fl OH5 2.061(6) 2.01(2) 2.15(2) OH5 2.251(1) grams are constructed for the Fe-C-P-O-H system in normal body uid Volume (Å3) 12.110(5) 12.155 13.1092 12.581 condition (Bigi et al., 2005; Waugh and Grant, 2010) and potential Distortion 0.04367 0.0522 0.0115 0.0417 surface water condition (Lee and Wilkin, 2010)(Fig. 7). The Eh-pH C O1 1.298(7) 1.29(1) 1.40(5) C O1 1.286(4) diagrams are drawn by considering equilibrium between chukanovite O2 1.275(9) 1.27(1) 1.15(5) O2 1.2831(18) and siderite (Fig. 7). Azoulay et al. (2012) reported that the chukano- O3 1.293(9) 1.28(1) 1.44(6) O3 1.284(1) vite can be obtained by corrosion of carbon steel in neutral and alkaline Distortion 0.0071 0.0039 0.0909 0.0008 conditions. This is consistent with the two Eh-pH diagrams (Fig. 7). The (1) This study; (2) Pekov et al., 2007; (3) Pignatelli et al., 2014; (6) Perchiazzi, diagrams show that the increasing pH is responsible for promoting the 2006. precipitation of chukanovite over siderite because the high concentra- fi – Note: The distortion index based on bond lengths was de ned by Baur, 1974. tion of OH ions favors the precipitation of chukanovite, which is also in agreement with other reported experiments (Nishimura, 2009; Lee and (Fig. 7a). The XRD results also show the oxidation routes from the core Wilkin, 2010; Azoulay et al., 2012). to the outer part in the oxidized carbon steel (Fig. 2). In normal surface The oxidation-reduction pathway for chukanovite was not reported water or groundwater systems (pH = 6.0 to 8.5), the pathway of side- in detail. Previous studies reported that goethite is the main oxidation rite/chukanovite to goethite can be the main oxidation route (Fig. 7b). product of chukanovite (Saheb et al., 2008; Azoulay et al., 2014). From The diagrams can also explain the biogenic chukanovite that produced fl the Eh-pH diagram, two possible oxidation routes in human body uid by the microbial reduction of Fe2+-excess magnetite (Kukkadapu et al., conditions (pH = ~7.4) are siderite/vivianite to goethite or siderite/ 2005). chukanovite to goethite via magnetite according to the diagram

Table 1 Unit cell parameters of chukanovite with malachite-rosasite group (Å).

Me2+ abcβ Ref.

Chukanovite Fe 12.402(2) 9.414(1) 3.216(1) 97.73(3) (1) 12.396(1) 9.407(1) 3.2152(3) 97.78(2) (2) 12.5(3) 9.5(2) 3.2(1) 97.6(5) (3) Glaukosphaerite (Cu, Ni) 12.0613(4) 9.3653(4) 3.1361(1) 98.085(5) (4) Pokrovskite Mg 12.2396(4) 9.3506(4) 3.1578(1) 96.445(5) (4) Parádsasvárite Zn 12.253(4) 9.348(3) 3.167(1) 97.700(4) (5) Rosasite (Cu, Zn) 12.8976(3) 9.3705(1) 3.1623(1) 110.262(3) (5) Mcguinnessite (Mg,Cu) 12.9181(4) 9.3923(2) 3.1622(1) 111.233(3) (6) Malachite Cu 11.974 9.502 3.24 98.75 (7)

(1) This study; (2) Pekov et al., 2007; (3) Pignatelli et al., 2014; (4) Perchiazzi and Merlino, 2006; (5) Perchiazzi et al., 2017; (6) Perchiazzi and Merlino, 2006; (7) Zigan et al., 1977.

Note: The unit cell parameters are based on P21/a setting.

186 S. Lee, H. Xu Chemical Geology 488 (2018) 180–188

Acknowledgements

This research was funded by NASA Astrobiology Institute (NNA13AA94A). Authors thank the Geology Museum of the University of Wisconsin–Madison for proving the sample. Authors also thank Mr. Franklin Hobbs, Prof. David Mogk, and two anonymous reviewers for their comments and suggestions.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https:// doi.org/10.1016/j.chemgeo.2018.04.033.

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