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Frost, Ray& Xi, Yunfei (2013) A vibrational spectroscopic study of the so-called ‘healing’ pa- pagoite CaCuAlSi2O6(OH)3. Spectroscopy Letters, 46(5), pp. 344-349.

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2 CaCuAlSi2O6(OH)3 3 4 Ray L. Frost, Yunfei Xi 5 6 School of Chemistry, Physics and Mechanical Engineering, Science and Engineering 7 Faculty, Queensland University of Technology, GPO Box 2434, Brisbane Queensland 8 4001, Australia. 9 10 11 Abstract 12 Papagoite is a named after an American Indian tribe and was used as a

13 healing mineral. Papagoite CaCuAlSi2O6(OH)3 is a hydroxy mixed anion compound with 14 both silicate and hydroxyl anions in the formula. The structural characterisation of the 15 mineral papagoite remains incomplete. Papagoite is a four membered ring silicate with Cu2+ 16 in square planar coordination. -1 17 The intense sharp Raman band at 1053 cm is assigned to the ν1 (A1g) symmetric stretching

18 vibration of the SiO4 units. The splitting of the ν3 vibrational mode offers support to the

19 concept that the SiO4 tetrahedron in papagoite is strongly distorted. A very intense Raman -1 -1 20 band observed at 630 cm with a shoulder at 644 cm is assigned to the ν4 vibrational modes. -1 21 Intense Raman bands at 419 and 460 cm are attributed to the ν2 bending modes. 22 Intense Raman bands at 3545 and 3573 cm-1 are assigned to the stretching vibrations of the 23 OH units. Low intensity Raman bands at 3368 and 3453 cm-1 are assigned to water 24 stretching modes. It is suggested that the formula of papagoite is more likely to be

25 CaCuAlSi2O6(OH)3·xH2O. Hence, vibrational spectroscopy has been used to characterise the 26 molecular structure of papagoite. 27 28 Key words: papagoite, stringhamite, cupric ions, healing mineral, vibrational spectroscopy 29 30 31 32

 Author to whom correspondence should be addressed ([email protected]) P +61 7 3138 2407 F: +61 7 3138 1804 1

33 Introduction

34 The mineral papagoite CaCuAlSi2O6(OH)3 is known from two locations in narrow 35 veinlets in altered granodiorite porphyry from Ajo, and in crystals, 36 Messina, South Africa [1, 2]. The mineral is a hydroxy silicate of , and 37 . It is one of a number copper silicates [3]. 38 39 There are a significant number of silicate which have copper as one of the main

40 cations. These include chrysocolla (Cu, Al)2H2Si2O5(OH)4·nH2O, dioptase CuSiO3·H2O,

41 planchéite Cu8Si8O22(OH)4·H2O, Cu5(SiO3)4(OH)2,whelanite

42 Ca5Cu2(OH)2CO3,Si6O17·4H2O, (K,Na)Cu7AlSi9O24(OH)6·3H2O, apachite

43 Cu9Si10O29·11H2O, papagoite CaCuAlSi2O6(OH)3. Apart from chrysocolla which 44 appears as an amorphous non-diffracting mineral, all of these copper silicate minerals are 45 highly crystalline. All of the minerals contain either hydroxy units or water units or both. 46 These water and OH units are important for the stability of the minerals. All these 47 minerals are of various shades of blue. 48 49 The mineral papagoite is named after the Papago tribe of Arizona. The native American 50 tribes have been known to use copper silicate minerals as healing antiseptic medicines. A 51 common feature of these silicate minerals is that these copper containing silicate 52 minerals have been traditionally used as ‘healing’ minerals [4]. Copper is very important 53 in human health but is toxic at higher concentrations [5]. Copper ions are of course a 54 very powerful antibacterial agent [4, 6, 7]. Copper compounds are used as antibacterial 55 agents. Estimation of the amount of copper in water and foods can be measured [8, 9]. 56 57 The mineral papagoite is monoclinic with point group 2/m [3]. The crytal structure was 58 refined by Groat and Hawthorne [10].The cell data is: : C2/m: a = 12.926(3), b 59 = 11.496(3), c = 4.696(1), β = 100:81(2)± Z = 4 [11]. Papagoite is one of only a few four 60 membered ring silicates [11]. These silicates have four silicate tetrahedrons linked into a ring 61 forming a distorted square-like structural element [3].

62 Raman spectroscopy has proven very useful for the study of minerals [12-19]. Indeed Raman 63 spectroscopy has proven most useful for the study of diagenetically related minerals as often 64 occurs with minerals containing copper and silicate groups. This paper is a part of systematic 65 study of vibrational spectra of minerals of secondary origin in the oxide zone. The

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66 objective of this research is to report the Raman spectra of papagoite and to relate the spectra 67 to the molecular structure of the mineral. Papagoite is known as a healing mineral. The 68 question arises as to whether there is any evidence that papagoite is actually a healing 69 mineral. 70 71 Experimental 72 Mineral

73 The mineral papagoite CaCuAlSi2O6(OH)3 was supplied by the Mineralogical Research 74 Company. The mineral originated from the new Cornelia Mine, Ajo, Pima County, 75 Arizona, USA. The mineral sample is defined as a ‘type’ mineral and is used as a 76 reference for this type of mineral and its structure. Details of the mineral have been 77 published (page 617) [20]. 78 79 Raman spectroscopy 80 81 Crystals of papagoite were placed on a polished metal surface on the stage of an Olympus 82 BHSM microscope, which is equipped with 10x, 20x, and 50x objectives. The spectra are 83 collected from a mixture of non-oriented crystals. The microscope is part of a Renishaw 1000 84 Raman microscope system, which also includes a monochromator, a filter system and a CCD 85 detector (1024 pixels). The Raman spectra were excited by a Spectra-Physics model 127 He- 86 Ne laser producing highly polarised light at 633 nm and collected at a nominal resolution of 2 87 cm-1 and a precision of ± 1 cm-1 in the range between 200 and 4000 cm-1. Repeated 88 acquisitions on the crystals using the highest magnification (50x) were accumulated to 89 improve the signal to noise ratio of the spectra. Spectra were calibrated using the 520.5 cm-1 90 line of a wafer. A spectrum of papagoite is provided on the RRUFF data base. The 91 spectra have been downloaded and are shown in the supplementary information. 92 93 Infrared spectroscopy 94 95 Infrared spectra were obtained using a Nicolet Nexus 870 FTIR spectrometer with a smart 96 endurance single bounce diamond ATR cell. Spectra over the 4000525 cm-1 range were 97 obtained by the co-addition of 128 scans with a resolution of 4 cm-1 and a mirror velocity of 98 0.6329 cm/s. Spectra were co-added to improve the signal to noise ratio. The infrared spectra 99 are given in the supplementary information.

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100 101 Spectral manipulation such as baseline correction/adjustment and smoothing were performed 102 using the Spectracalc software package GRAMS (Galactic Industries Corporation, NH, 103 USA). Band component analysis was undertaken using the Jandel ‘Peakfit’ software package 104 that enabled the type of fitting function to be selected and allows specific parameters to be 105 fixed or varied accordingly. Band fitting was done using a Lorentzian-Gaussian cross-product 106 function with the minimum number of component bands used for the fitting process. The 107 Gaussian-Lorentzian ratio was maintained at values greater than 0.7 and fitting was 108 undertaken until reproducible results were obtained with squared correlations of r2 greater 109 than 0.995. 110 111 Results and Discussion 112 113 The Raman spectrum of papagoite in the 100 to 4000 cm-1 range is displayed in Figure 1a. 114 This spectrum shows the relative intensities of the different bands in the Raman spectrum of 115 papagoite. It is obvious that there are large parts of the spectrum where no peaks are 116 observed. The spectrum is then subdivided into sections depending upon the type of 117 vibrations being recorded. The infrared spectrum of papagoite is reported in Figure 1b. 118 Again the relative intensities of the infrared bands may be observed and a comparison of 119 intensities with the Raman spectrum observed. Again in the infrared spectrum, there are 120 whole sections where no bands are observed. The spectra are subdivided into sections for 121 more detail. 122 123 The Raman spectrum of papagoite in the 800 to 1200 cm-1 region is reported in Figure 2. The

124 spectrum consists of a series of sharp bands, most of which are the vibrational modes of SiO4 -1 125 units. The intense sharp Raman band at 1053 cm is assigned to the ν1 (A1g) symmetric 126 stretching vibration. A low intensity shoulder is observed at 1079 cm-1. In the spectrum 127 downloaded from the RRUFF data base this band is observed at 1054 cm-1 with a second 128 band at 1084 cm-1. Vedanand et al. observed a band at 800 cm-1 for the mineral stringhamite

129 and defined this band to be the ν1 SiO4 vibration. However this does not appear to be in 130 agreement with this work. According to Farmer [21], this band for zircon is observed at 974 131 cm-1. As pointed out by Vedanand et al. [22], the distorted Cu2+ ion effects the symmetry of

132 the SiO4 units. This results in a shift in band position to higher wavenumbers. The EPR 133 results of Vedanand et al. for stringhamite prove that the Cu2+ ion is in a square planar 4

134 environment and the bonding between the Cu2+ ion and the ligands in the square 135 planar coordination is very strong. 136 137 The infrared spectrum of papagoite in the 500 to 1300 cm-1 region is shown in Figure 2a. 138 The spectrum shows complexity with a significant number of component bands. A series of 139 intense infrared bands are observed at 958, 1027, and 1084 cm-1. These bands are assigned to

140 the ν3 (Eu , A2u, B1g) SiO4 antisymmetric stretching vibrations. The Raman bands associated 141 with these vibrational modes are found at 867, 942 and 986 cm-1. The bands were observed

142 in the identical position in the RRUFF papagoite spectrum. The splitting of the ν3 vibrational

143 mode offers support to the concept that the SiO4 tetrahedrons in papagoite are strongly 144 distorted. 145 1 146 This concept is further supported by the observation of multiple ν4 bands at around 600 cm -1 147 (Figure 3a). For a perfectly symmetric SiO4 tetrahedron, only a single band at 608 cm (A2u) -1 148 should be observed. A sharp band is observed at 630 cm and is assigned to the SiO4 ν4 149 bending mode. A second band is observed at 755 cm-1 and may also be assigned to this 150 vibrational mode. Infrared bands of papagoite (Figure 2b) are found at 644, 695, 718, 725 151 and 750 cm-1. Other bending modes occur below 500 cm-1 which is below the lower limit of -1 152 the ATR technique. Vedanand et al. reported the ν2 and ν4 modes at 510 and 660 cm . 153 -1 154 The strong Raman bands at 419 and 460 cm are assigned to the ν2 SiO4vibrational modes.

155 According to Farmer [21], the ν2 in-plane bend for a perfect SiO4 tetrahedron should be found 156 at 439 cm-1. Vedanand et al. observed an infrared band at 510 cm-1 for stringhamite and

157 assigned the band to the ν2 vibrational mode. The splitting of the ν2 vibrational mode

158 strongly supports the concept of a strongly distorted SiO4 tetrahedron. Raman bands are 159 observed at 469 and 474 cm-1 in the RRUFF spectrum. Other bands were found at 535, 568, 160 575 and 628 cm-1 in the RRUFF spectrum. The Raman spectrum of papagoite in the 100 to 161 300 cm-1 region is shown in Figure 3b. Intense Raman bands are observed at 251, 264, 279 162 and 298 cm-1. These Raman bands are attributed to AlO, CuO and CaO stretching 163 vibrations. 164 165 The Raman and infrared spectra of the hydroxyl stretching region of papagoite is displayed in 166 Figures 4a and 4b respectively. Two intense Raman bands are observed at 3545 and 3573 167 cm-1 and are attributed to the stretching vibrations of the OH units of the papagoite mineral 5

168 CaCuAlSi2O6(OH)3. Two Raman bands of lower intensity are observed at 3368 and 3453 169 cm-1. These bands are assigned to water stretching vibrations. The infrared spectrum shows 170 much greater complexity. A series of infrared bands are observed at 3537, 3547, 3572, 3619, 171 3630, 3652, 3668 and 3690 cm-1. These bands are assigned to the stretching vibrations of the 172 OH units. Infrared bands are also observed at 3170, 3375 and 3450 cm-1. These bands are 173 attributed to water stretching vibrations. It is tempting to suggest that water is chemically 174 bonded in the papagoite structure. It is possible that the formula should be -1 175 CaCuAlSi2O6(OH)3·xH2O. The infrared spectrum in the 1300 to 1800 cm region is shown 176 in Figure 5. Two bands are observed at 1633 and 1684 cm-1. These bands are assigned to 177 water bending modes. The position of the bands suggests that water is strongly hydrogen 178 bonded in the water structure. The bands at 1426 cm-1 with a component band at 1503 cm-1 179 are assigned to OH deformation modes. 180

181 Papagoite CaCuAlSi2O6(OH)3 as a healing mineral 182 183 Is there any truth in the statement that papagoite is a healing mineral [4]? It is well known 184 that various American Indian tribes used copper silicate minerals as healing minerals. After 185 all this mineral (papagoite) is named after an Arizonian Indian tribe. There is certainly a great 186 deal of literature on the subject of minerals being healing agents, especially on the internet [5, 187 23]. It is well known that Cu2+ is a very powerful antibacterial agent [7, 24, 25]. Copper 188 compounds are used as fungicides. For example copper sulphate is used in agriculture as an 189 antifungal agent. It is well known that copper is essential for human health, although too 190 much copper can be toxic [5]. Copper compounds such as copper hydroxy chloride and 191 cupric formate are used as antibacterial agents in swimming pools and is a powerful 192 antibacterial agent in open latrines. 193 194 In the laboratory, silicate minerals are shown to dissolve in hydrolysis reactions. + + 3+ 195 For example: KAlSi3O8 (s) + 4H (aq) + 4H2O (l) = K (aq)+ Al (aq) + 3H4SiO4 (aq) 196 The dissolution of orthoclase, as shown above, occurs through a hydrolysis reaction driven 197 only by pH. Because reaction rates depend on the chemical potential, the rate at which 198 orthoclase dissolves in hydrolysis reactions is a function of pH. 199 200 The question arises as to whether a mineral such as papagoite can provide very low 201 concentrations of copper ions. The following reaction is envisaged: 6

2+ 202 CaCuAlSi2O6(OH)3 (s) + 3H+ (aq) → Cu (aq) + CaSiO3 (aq)+ AlSiO3 (aq) + 3H2O 203 The reaction above depends upon exchange of copper ions with other ions such as the 204 hydrogen ion in an aqueous medium. In effect, the equation represents acid leaching. The 205 above chemical reaction offers a mechanism for the release of Cu 2+ ions. These copper ions 206 can then function as an antiseptic agent. 207 208 Even if very low concentrations of Cu 2+ ions exist, it means that the mineral can function as

209 a healing mineral. If we use a simplified form of papagoite, namely CuSiO3·H2O, then the 210 following reaction can occur: . + 2+ 211 CuSiO3 H2O (s) + 2H (aq) = Cu (aq) + H4SiO4 (aq) 2+ + 2 212 K(sp) = [Cu ][H4SiO4]/[H ] 213 Thus, a solubility product can be estimated. What this reaction proves is that under acid 214 conditions copper silicate minerals can release copper ions to the environment. So if the 215 mineral papagoite for example is rubbed on the skin, the acidity of the skin will release 216 copper ions. In other words, there is evidence that the mineral papagoite acts as a healing 217 mineral. 218

219 Conclusions 220 Vibrational spectroscopy has been used to characterise the molecular structure of the mineral 221 papagoite. From an X-ray crystallographic point of view, the structure is unknown. The 222 vibrational spectra of the mineral are complex. Multiple silicate vibrations are observed. 223 Multiple silicate stretching vibrations suggest that the silicate units in the papagoite structure 224 are non-equivalent. Multiple hydroxyl and water bands are observed.

225 Estimations of the solubility product of papagoite show that Cu2+ ions are released under the 226 influence of low pH. The leaching of copper ions results in the release of the Cu2+ ions. 227 These Cu2+ ions can then function as healing/antiseptic agents. The native American Indians 228 used copper silicate mineral in their culture as healing minerals and this work shows that their 229 use was based on good science.

230

231 Acknowledgments

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232 The financial and infra-structure support of the Queensland University of Technology, 233 Chemistry discipline is gratefully acknowledged. The Australian Research Council (ARC) is 234 thanked for funding the instrumentation. 235 236

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237 References 238 [1] B. Cairncross, The Messina mining district, South Africa, Mineralogical Record, 22 239 (1991) 187-199. 240 [2] C.O. Hutton, A.C. Vlisidis, Papagoite, a new copper-bearing mineral from Ajo, Arizona, 241 American Mineralogist, 45 (1960) 599-611. 242 [3] C. Guillebert, T. Le Bihan, Structure investigation of copper silicates. Atomic structure of 243 papagoite, Bulletin de la Societe Francaise de Mineralogie et de Cristallographie, 88 (1965) 244 119-121. 245 [4] R.E. Ferrell, Jr., Medicinal clay and spiritual healing, Clays and Clay Minerals, 56 (2008) 246 751-760. 247 [5] M. Araya, M. Olivares, F. Pizarro, Copper in human health, International Journal of 248 Environment and Health, 1 (2007) 608-620. 249 [6] J. Drelich, B.-W. Li, P. Bowen, J.-Y. Hwang, O. Mills, D. Hoffman, Vermiculite 250 decorated with copper nanoparticles: Novel antibacterial hybrid material, Applied Surface 251 Science, 257 (2011) 9435-9443. 252 [7] C. Hu, M. Xia, Antibacterial effect of copper-bearing montmorillonite on aquacultural 253 pathogenic bacteria and its mechanism, Guisuanyan Xuebao, 33 (2005) 1376-1380. 254 [8] K. Watanabe, Minerals contained in crops essential to human health, Biomedical 255 Research on Trace Elements, 20 (2009) 263-273. 256 [9] H. Yasuda, Diagnostic estimation of toxic metals using hair mineral analysis, BIO 257 Clinica, 25 (2010) 151-154. 258 [10] L.A. Groat, F.C. Hawthorne, Mineralogy and Petrology, 37 (1987) 89. 259 [11] L.A. Groat, F.C. Hawthorne, Refinement of the of papagoite, 260 CaCuAlSi2O6(OH)3, Mineralogy and Petrology, 37 (1987) 89-96. 261 [12] S. Bahfenne, L. Rintoul, R.L. Frost, Single-crystal Raman spectroscopy of natural 262 leiteite (ZnAs2O4) and comparison with the synthesised mineral, J. Raman Spectrosc., 42 263 (2011) 659-666. 264 [13] H. Cheng, Q. Liu, J. Yang, J. Zhang, R.L. Frost, X. Du, Infrared spectroscopic study of 265 halloysite- acetate intercalation complex, J. Mol. Struct., 990 (2011) 21-25. 266 [14] R.L. Frost, S.J. Palmer, A vibrational spectroscopic study of the mineral corkite 267 PbFe33+ (PO4,SO4)2(OH)6, J. Mol. Struct., 988 (2011) 47-51. 268 [15] R.L. Frost, S.J. Palmer, H.J. Spratt, W.N. Martens, The molecular structure of the 269 mineral beudantite PbFe3(AsO4,SO4)2(OH)6 - Implications for arsenic accumulation and 270 removal, J. Mol. Struct., 988 (2011) 52-58. 271 [16] R.L. Frost, S.J. Palmer, Y. Xi, A vibrational spectroscopic study of the mineral 272 hinsdalite (Pb,Sr)Al3(PO4)(SO4)(OH)6, J. Mol. Struct., 1001 (2011) 43-48. 273 [17] R.L. Frost, Y. Xi, S.J. Palmer, Molecular structure of the mineral woodhouseite 274 CaAl3(PO4,SO4)2(OH)6, J. Mol. Struct., 1001 (2011) 56-61. 275 [18] R.L. Frost, Y. Xi, S.J. Palmer, Are the 'cave' minerals archerite (K,NH4)H2PO4 and 276 biphosphammite (K,NH4)H2PO4 identical? A molecular structural study, J. Mol. Struct., 277 1001 (2011) 49-55. 278 [19] S.J. Palmer, R.L. Frost, The structure of the mineral arthurite 279 CuFe23+(AsO4,PO4,SO4)2(O,OH)2·4H2O - A Raman spectroscopic study, J. Mol. Struct., 280 994 (2011) 283-288. 281 [20] J.W. Anthony, R.A. Bideaux, K.W. Bladh, M.C. Nichols, Handbook of Mineralogy, 282 Mineral Data Publishing, Tuscon, Arizona, USA, 1995. 283 [21] V.C. Farmer, Mineralogical Society Monograph 4: The Infrared Spectra of Minerals, 284 1974. 285 [22] S. Vedanand, B.J. Reddy, Y.P. Reddy, Spectroscopic investigations on stringhamite, 286 Ca[Cu(SiO4)](H2O), Solid State Communications, 77 (1991) 231-234. 9

287 [23] M. Baeckstroem, S. Saedbom, Risk assessment of historical mine waste using chemical 288 analysis and ocular mineral/rock classification - a comparison, Publications of the 289 Australasian Institute of Mining and Metallurgy, 8/2008 (2008) 85-90. 290 [24] A. Hirai, Process for preparing copper oxide-coated antibacterial material, in, (Japan). 291 Application: US 292 US, 2006, pp. 9pp. 293 [25] F. Ohashi, Practical lecture of inorganic antibacterial agents. 11. 5. Inorganic antifungal 294 agents. 2. Silver, copper, zinc/complex salt. 2. Clay mineral. antibacterial and antifungal 295 agents, Bokin Bobai, 25 (1997) 105-111. 296 297 298

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299 List of Figures 300 301 Figure 1 (a) Raman spectrum of papagoite in the 100 to 4000 cm-1 region (b) Infrared 302 spectrum of papagoite in the 500 to 4000 cm-1 region. These spectra show the complete 303 spectra over the complete spectral range. 304 305 Figure 2 (a) Raman spectrum of papagoite in the 800 to 1200 cm-1 region (b) Infrared 306 spectrum of papagoite in the 500 to 1300 cm-1 region. 307 308 Figure 3 (a) Raman spectrum of papagoite in the 300 to 800 cm-1 region (b) Raman spectrum 309 of papagoite in the 100 to 300 cm-1 region. 310 311 Figure 4 (a) Raman spectrum of papagoite in the 3200 to 3800 cm-1 region (b) Infrared 312 spectrum of papagoite in the 2600 to 3800 cm-1 region. 313 314 Figure 5 Infrared spectrum of papagoite in the 1300 to 1800 cm-1 region. 315 316 317 318 319

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320

Figure 1a Figure 1b 321 322 323

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324

Figure 2a Figure 2b 325 326 327 328

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329

Figure 3a Figure 3b 330 331 332 333

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334

Figure 4a Figure 4a 335 336 337 338

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339 340 341 Figure 5

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