Much More Than a Glass: The Complex Magnetic and

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Much More than a Glass: the Complex Magnetic and Microstructural Properties of Obsidian Valentina Mameli, Anna Musinu, Daniel Niznansky, Davide Peddis, Guido Ennas, Andrea Ardu, Carlo Lugliè, and Carla Cannas J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.6b08387 • Publication Date (Web): 01 Nov 2016 Downloaded from http://pubs.acs.org on November 9, 2016

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The Journal of Physical Chemistry

Much More Than a Glass: the Complex Magnetic and Microstructural Properties of Obsidian Valentina Mameli§†, Anna Musinu§†, Daniel Niznansky﬩, Davide Peddis#, Guido Ennas§†, Andrea Ardu§†‡, Carlo Lugliè□, Carla Cannas§†‡* §

Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, Cittadella Universitaria, Monserrato, 09042, Italy

†

Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), Cagliari Unit, Italy

﬩

Department of Inorganic Chemistry, Charles University of Prague, Prague 2, 128 43, Czech Republic

#

Institute of Structure of Matter, National Research Council (CNR), Monterotondo Scalo, 00015, Italy ‡

□

Consorzio AUSI, CREATE, Palazzo Bellavista Monteponi, Iglesias, 09016, Italy

Dipartimento di Storia, Beni Culturali e Territorio, Università di Cagliari, Cittadella dei Musei, Cagliari, 09124, Italy

*Corresponding author: Prof. Carla Cannas ([email protected])

ACS Paragon Plus Environment

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ABSTRACT

Obsidian is a natural volcanic glass in which nanocrystalline and microcrystalline phases can coexist with the glassy one. In this paper, magnetic properties of Monte Arci obsidians are investigated by an experimental approach commonly applied to synthetic nanostructured materials and rarely to natural ones, and correlated with the mineralogical composition and microstructure. Among the different crystalline phases, the iron-containing components are found to be responsible

for

a

great

variety

of

magnetic

behaviors,

including

paramagnetism,

antiferromagnetism, ferromagnetism and superparamagnetism. The combined use of Powder XRay Diffraction (PXRD),

57

Fe Mössbauer Spectroscopy, DC magnetometry and Transmission

Electron Microscopy (TEM/HRTEM) provides new insights in the Monte Arci obsidian: (i) the presence of magnetite nanoparticles spread into the glassy matrix; (ii) the presence of an antiferromagnetic phase responsible for a discontinuity at about 45 K; (iii) exchange bias phenomena, for the first time revealed in obsidians, due to the coupling between the nanostructured ferrimagnetic phase and the antiferromagnetic one; (iv) Goldanskii-Karyagin effect (GKE) associated with biotite.

INTRODUCTION Obsidian is a dark volcanic glass originated by fast cooling of acidic lavas (65-75% SiO2).1 In the literature, most of the studies about obsidian are dedicated to the application of an analytical technique, both destructive and non-destructive, with the aim of discriminating the main sources and sub-sources for archaeological purposes. Other studies are devoted to the characterization of the obsidian as a material2–19 dealing with different aspects as the color or optical properties8,9,12,17, the glass structure6,10,11, the comparison of its properties with those of


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impact glasses13,19 or artificial ones2,4, its formation process7,16,18, the different coordination of iron ions3–5 and the paleointensity studies14,15. Previous works have been also devoted to the study of the magnetic properties of obsidian samples of different sources worldwide by magnetometry3,14– 16,19–26

, EPR5,8,27,28 and

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Fe Mössbauer Spectroscopy3,4,8,20–22,27,29,30 among which some refer to

Sardinian obsidians20,22,24,27–29. The great majority of the authors evidenced the coexistence of paramagnetism with ferrimagnetism and/or superparamagnetism associated with magnetite nanoparticles. Some authors underlined the possibility to distinguish magnetite of different sizes from single domain to multi domain.16,19,21,22,24 However, to date a comprehensive correlation of the magnetic properties with the microstructure and morphology of Monte Arci obsidian is still lacking, despite the evidences for the copresence of a glassy matrix together with iron-containing micro- or nanolites. Indeed, although obsidian is usually defined as a natural glass, it is known from the literature that crystalline inclusions and occlusions2–18,20–37, among which iron-based minerals, are often present, also in the case of the Monte Arci obsidian.20,24,27,28,31,34,35 Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8)2,7,9,11,18,20,21,31, pyroxenes (XY(Si,Al)2O6)6,7,9,18,31, biotite (K(Mg,Fe)3AlSi3O10(OH)2)6,20,31, hornblende ((Ca,Na)2-3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2)7,18,21, silica polymorphs (cristobalite, tridymite, quartz)11,31,33, apatite (Ca10(PO4)6(OH,F,Cl)2)18,31, zircon (ZrSiO4)18,33, titanomagnetite/magnetite or related spinels (Fe3O4, Fe2+(Fe3+,Ti)2O4)3,5–7,12,18,19,21– 31,33

, hematite (α-Fe2O3)21–23,25–28, ilmenite (FeTiO3)18,25,28,31, pyrrhotite (Fe(1-x)S (x = 0 to 0.2))18,

pyrite (FeS2)31, metallic iron27, pseudo-brookite (TiO2)28, olivine ((Mg2+,Fe2+)2SiO4)31, monazite ((Ce,La,Nd,Th)PO4)31 have been reported for obsidians of different sources. Among the pyroxenes, clinopyroxenes sometimes in synneusis with magnetite6,31, pigeonite ((Ca,Mg,Fe)(Mg,Fe)Si2O6)7,

augite

((Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6)7,

hedenbergite


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(CaFe2+Si2O6)9, orthopyroxenes31, hypersthene ((Mg,Fe)SiO3)7, mixed pyroxenes (Cpx-Opx)7 can be present. Among feldspars, sanidine (K(AlSi3O8))18, plagioclase (albite-anorthite series, NaAlSi3O8 to CaAl2Si2O8)7,18,21,31, anorthoclase ((Na,K)AlSi3O8)31 and in particular Na-rich feldspars9,11 have been reported. In particular for Monte Arci obsidian, some authors (Acquafredda et al.) have already suggested a classification as glassy rhyolite instead of obsidian, due to the abundance of microphenocrysts and microcrysts of biotite, feldspars and the presence of magnetite, ilmenite, monazite and pyroxenes as minor minerals.31,35 The resulting dual crystalline-amorphous nature renders their study rather complex. However, even if from one hand the complexity of the system increases by increasing of the number of minerals embedded into the glassy phase, on the other hand, the presence of the crystalline phases can be taken as an advantage because of the possibility of characterizing the system by diverse consolidated chemical-physical techniques. In this work, Monte Arci (Sardinia) obsidians coming from different geochemical sites have been investigated by an experimental approach based on a multitechnique characterization, usually applied to synthetic nanostructured magnetic materials38–41 but rarely to natural ones, to get new insights on the magnetic properties and correlate them with the mineralogical composition and the microstructure. With this aim, DC magnetometry protocols as Zero Field Cooled – Field Cooled and field dependence magnetization recorded at different temperatures in post ZFC and FC conditions, magnetization versus magnetic field measurements, Powder X-Ray Diffraction (PXRD) and Rietveld analysis,

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Fe Mössbauer Spectroscopy and Transmission Electron

Microscopy (TEM and HR-TEM) have been applied to obsidian samples from Monte Arci. This approach gave the possibility to draw a picture of the magnetic complexity of Monte Arci obsidian,


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revealing a coexistence of paramagnetic, antiferromagnetic, superparamagnetic and ferrimagnetic behaviors ascribable to different micro- and nanocrystalline iron-bearing phases. EXPERIMENTAL SECTION Materials This study has been performed on twelve obsidian samples, coming from the four geochemical sources (SA, SB1, SB2, SC), collected in the Monte Arci (Sardinia) and geographically localized as reported in Figure S1-2 and Table S1. They were selected among the more than 500 samples characterized in the Lithotypes collection stored at the Laboratory of Sardinian Antiquities and Paleoethnology of the University of Cagliari (LASP). Samples were used to draw the published Geo-chemical map of the Monte Arci obsidian distribution.42 The precise position of each sample has been GPS recorded: as shown in Figure S1, each specimen was assigned to a specific geo-chemical family, according to the elemental composition obtained by means of many different techniques (INAA, PIXE, EMP-WDS, XRF, pXRF, SEMEDS, etc.). Methods Obsidian samples were first prepared by milling on an agate mortar and then by means of a ball milling Fritch Pulverizete 5, equipped by agate jar and agate balls for six hours at 100 rpm. During this period, three minutes of milling were followed by six minutes of break in order to avoid any heating of the powder. The as-obtained powders have been sieved at 400 meshes (37 μm). Structural characterization was carried out by Powder X-Ray Diffraction (PXRD) with a conventional θ-θ Bragg–Brentano focalizing geometry Seifert x3000, Cu Kα wavelength (λ=1.54056 Å), graphite monochromator on the diffracted beam and scintillation counter. The


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PXRD sample was cavity back loaded to minimize preferred orientations. Qualitative analysis of PXRD spectra was carried out by using Analyze software and the PDF database (PCPDF-WIN, JCPDS-International Center for Diffraction Data, Swarthome, PA). The calibration was performed by means of a standard silicon sample and using the Warren correction. Quantitative phase analysis were also evaluated by the Rietveld method using the MAUD software43,44 and recommended fitting procedures were adopted. Structural models of the identified phases were obtained by Inorganic Crystal Structure Database (ICSD, Karlsruhe, Germany). Lattice parameters, average crystalline size, and weight content for each phase were refined. The simulation of aluminum silica glass was carried out by means of Le Bail model.45,46 A correction procedure for preferred orientation along the biotite [002] planes was run by means of March-Dollase function.47 During the Rietveld analysis, different start points were attempted to achieve a better estimation of the error related to the phases’ contents. A final weighted index of agreement, Rw (%), lower than 7.0 % was obtained for all the samples. The 57Fe Mössbauer spectra were measured in the transmission mode with 57Co diffused into a Rh matrix as the source moving with constant acceleration. The spectrometer (Wissel) was calibrated by means of a standard α–Fe foil and the isomer shift was expressed with respect to this standard at 293 K. The samples were measured at room temperature (293 K) in the absence of an external magnetic field. On one sample (N408), a further measurement was carried out at 4 K. The fitting of the spectra was performed by NORMOS program using Lorentzian profiles. The magnetic properties were studied by using a Quantum Design SQUID magnetometer (Hmax = ±55 kOe). Zero Field Cooled – Field Cooled (ZFC-FC) protocols were used to record the magnetization versus temperature curves within 5 K-300 K under different values of magnetic field. The ZFC curve was obtained heating the sample from 5 K to 300 K under magnetic field


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after a cooling process under a zero magnetic field. The FC curve was obtained by cooling the sample from 5 K to 300 K under a non-zero magnetic field. The morphological properties have been characterized by Transmission Electron Microscopy. A small amount of the milled sample was dispersed in 1-octanol. The dispersion was then dropped on a carbon-coated copper grid and left to dry for the TEM observations. The samples were observed in electron micrographs obtained with a conventional TEM (JEOL, Model 200CX) operating at 200 kV and a High Resolution TEM (JEM 2010 UHR) equipped with a Gatan imaging filter (GIF) with a 15 eV window and a 794 slow scan CCD camera. RESULTS & DISCUSSION 1. Magnetic measurements ZFC-FC protocols, commonly adopted to study the temperature-dependence of the magnetization for nanostructured artificial materials but never applied to obsidian to the best of our knowledge, have been used to analyze eight samples of Monte Arci obsidian (two for each geochemical source, see Figure S1-2 and Table S1 for the details on the geological setting and the samples morphology) (Figure S3). Here, as an example, the curves measured under a magnetic field of 25 Oe on the samples N141 are reported in Figure 1 together with three M vs H curves recorded at different temperatures (5 K, 30 K, 300 K). Three different regions (I, II, III) can be identified in the ZFC curve: a decrease of the magnetization down to about 25 K (I), a discontinuity at about 50 K (II) and a rough band that joins up to the FC curve at temperatures between 225 and 275 K (III). The region I is characterised by a decrease of the magnetisation with increasing temperature for both ZFC and FC curves. This trend can be related to a paramagnetic phase associated with iron ions dispersed within the glassy matrix and/or to paramagnetic iron-containing crystalline phases.


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The region II shows a discontinuity point at about 50 K in the ZFC curve. The difference (𝑀𝐹𝐶 − 𝑀𝑍𝐹𝐶 ), being a good approximation of 𝑀𝑇𝑅𝑀

48

, can be used to describe the energy profile (see Figure

S4). In fact, its first derivative gives an estimation of the energy barrier distribution (Figure 1b) centred at about 45 K. This temperature resulted to be magnetic field-independent within the experimental error (Figure S5), suggesting an antiferromagnetic-paramagnetic transition. The region III resembles typical ZFC-FC curves collected for an ensemble of ferro/ferrimagnetic monodomain nanoparticles. In all samples, ZFC and FC curves overlap at high temperatures whereas at lower temperatures they start to separate: the FC magnetization increases on decreasing the temperature, while the ZFC magnetization shows a broad peak. Such behaviour is characteristic for magnetic monodomain nanoparticles with a barrier energy distribution that, as the temperature increases, become superparamagnetic (unblocking process) according to their anisotropy energy and volume.38 Assuming temperature independent anisotropy and the absence of interparticle interactions, the temperature corresponding to the maximum in the ZFC curve ( 𝑇𝑚𝑎𝑥 ) can be considered directly proportional to the average blocking temperature (). The irreversible magnetic behaviour is observed below a certain temperature (𝑇𝑖𝑟𝑟 ) that is related to the blocking of the biggest particles.49,50 The

(𝑇𝑖𝑟𝑟 − 𝑇𝑚𝑎𝑥 )

values provide a qualitative measure of the magnetic

anisotropy distribution, which is strictly connected with the size distribution.50 The 𝑇𝑚𝑎𝑥 , 𝑇𝑖𝑟𝑟 and (𝑇𝑖𝑟𝑟 − 𝑇𝑚𝑎𝑥 )

values have been calculated and are equal to 169±8 K, 226±11, 57 K for the sample

N141 and 117±6 K, 203±10, 86 K for the sample N408. All these features, evidenced in the sample N141, are revealed to be common to all Monte Arci obsidian samples studied in this work (Figure S3).


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The magnetic behaviour of the sample N141 has been then investigated by measuring the magnetisation versus magnetic field curves at different temperatures in the range 5 K - 300 K (Figure S6) and, in particular, in Figure 1c, d, e the curves at 5 K, 30 K, 300 K are reported. The M vs H curves at 300 K show ferromagnetic like behavior (S-shaped curves). The saturation magnetisation value has been found at about 0.12 emu/g (normalized for the total mass of sample), which are in agreement with the values found by other authors for obsidian samples of different provenance, among which Sardinian ones.22–24,26 The hysteretic behaviour (Hc (N141) = 202±10 Oe; Mr/Ms (N141) = 0.13±0.01) allows to evidence the presence of a population of RT-blocked single-domain and/or multi-domain particles that accompany the population of superparamagnetic nanoparticles, evidenced by ZFC-FC curves. At 30 K, an increase of the slope at high field and a ferromagnetic behavior with Mr/Ms and Hc ≠0 is observed. These features have been already observed in some nanostructured anitiferromagnets.51–53 In particular, the linearity at high field is due to the expected antiferromagnetic-like behavior whereas the presence of uncompensated spins can be responsible for the ferromagnetic-like component. A further temperature decrease down to 5 K results in a completely different shape of the M vs H curves at high field. This difference can be ascribed to a dominant contribute of the paramagnetic component. This interpretation seems to be coherent with the findings based on the ZFC-FC curves supporting the idea of a coexistence of paramagnetic, antiferromagnetic and ferro/ferrimagnetic phases, which are predominant over the others within certain temperature ranges. Due to the presence of a ferrimagnetic phase and an antiferromagnetic one, experiments on five obsidian samples, act to evaluate possible exchange bias phenomena, commonly evidenced for synthetic multi-layers structures, core-shell and heterojunction54,55, have been performed by collecting hysteresis loops at 5 K after a Field Cooling protocol under a magnetic field of 2 T


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(Figure S7). Here, as an example, the measurements for N141 (SB2) are reported (Figure 2). The curves well resemble those obtained for synthetic antiferromagnetic/ferromagnetic interfaces with different composition56–58 characterised by a negative shift of the demagnetising branch of the hysteresis loop. A small exchange bias is observed as a consequence of the horizontal shift of the demagnetising branch. The shift may be quantified through the exchange field parameter HEB = (H+ + H-)/2, whereas H+ and H- being the points where the loop intersects the field axis.59 The exchange bias field normalized for the coercivity (HEB/Hc ) for N141 sample is  0.2. This value is small but of the same order of magnitude of some hybrid ferro/antiferromagnetic nanostructures (HEB/Hc (Co@Mn)0.35; HEB/Hc (Fe@Mn)0.4)60,61. It is worth to note that in the case of obsidian samples the extent of this effect is smaller probably due to the random occurrence of contact regions between the antiferromagnetic phase and the ferrimagnetic one rather than well-organised extended interfaces. This effect has been observed for all the samples (Figure S7), suggesting that this phenomenon, although of small entity, is characteristic of all the analysed Monte Arci obsidians. A further measurement on the N141 sample under a higher magnetic field (5 T) has allowed confirming that this effect is not an artefact (Figure 2a). In addition, a clear increase of the anisotropy (i.e. increase of Hc) and thermal stability (i.e. increase of Mr/Ms) is observed, as a further confirmation of the appearance of unidirectional magnetic anisotropy. 62 The temperature dependence of exchange bias phenomenon (Figure 2b) gives interesting information: HEB disappears around 50 K, suggesting a Néel temperature for the antiferromagnetic phase around this value and that the antiferro- and ferrimagnetic phases are in close contact. In order to clarify the correlation between the magnetic behaviour and the chemical composition, the samples have been studied also by PXRD and

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Fe Mössbauer Spectroscopy (Figure 3).


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Furthermore, to ensure a proper representativeness, the number of the analysed samples has been enlarged. 2. Powder X-Ray Diffraction (PXRD) PXRD patterns of twelve obsidians (Figure 3a) coming from different geochemical sources (Figure S1-2, Table S1) show an intense and broad band associated with the main contribute of a glassy matrix and several sharp peaks ascribable to various crystalline phases. The qualitative analysis suggests a similar mineralogical composition for all samples, but differences in the minerals content are evident as expected taking into account the dynamics of the eruptive events, independently on the geochemical group. The intense and broad band, centred at about 23°, is associated with the main contribute of a glassy matrix (>82 w%) and the several sharp reflections are ascribed to the following crystalline phases: albite (NaAlSi3O8), biotite (K(Fe,Mg)3[AlSi3O10(OH)2]), cristobalite (SiO2), spinel iron oxide (Fe3O4 or γ-Fe2O3 or titanomagnetite/titanomaghemite), quartz (SiO2) and pyroxene phases, attributed for simplicity by the endmembers enstatite (MgSiO3) and ferrosilite (FeSiO3), (Figure 3a) although both ortho- and clinopyroxenes seem to be compatible with the experimental profile. The weight percentages obtained by Rietveld analysis are listed in Table 1 and the PDF and ICSD cards numbers are reported in the Table S2. An example of curve fitting by Rietveld method is reported in Figure S8. The lower content of silica glass (82%) and the highest content of albite (10.7%) have been found in the N408 (SC) sample. On the contrary, in the sample N141 (SB2) the glassy matrix represents about the 94%. In addition, a significant amount of cristobalite (3-4%) and a low percentage of a spinel iron oxide (0.2-0.6%) with size in the nanometre range have been found in all samples in agreement with the magnetic data (ZFC-FC curves and RT M vs H curves). A value


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of saturation magnetisation of about 35 emu/g has been obtained for the sample N141 by normalising the hysteresis loop for the weight percentage of magnetite determined by Rietveld method. Taking into account the limits of the curve fitting by Rietveld for a such complex material, these values of Ms seem to agree with the values usually obtained for synthetic magnetite nanoparticles63,64 which are usually below the Ms value reported for bulk material (92 emu/g). Among the different crystalline phases, the iron-containing components have been also studied by 57Fe Mössbauer Spectroscopy. 3. 57Fe Mössbauer Spectroscopy All the RT Mössbauer spectra of the twelve samples (Figure 3b) show three sub-spectra: a broad and asymmetric doublet associated with a paramagnetic phase containing Fe2+ and two sextets, which belong to the tetrahedral and octahedral sites of the magnetite, a ferrimagnetic spinel iron oxide phase (see examples of curve fitting in Figure S9). The hyperfine parameters are listed in Table 2. The magnetic ordered spinel phase (two sextets) has been identified as magnetite rather than maghemite according to the hyperfine parameters (Table 2).65–67 Furthermore, Mössbauer data did not provide any evidence for the presence of titanomagnetite, being the isomer shift of the sextets for this phase usually in the range of 0.9 – 1.0 mm/s.68,69 Therefore, considering magnetite as the spinel phase present in the obsidian, from the Tmax values obtained by the ZFC curve it has been possible to roughly estimate the size of the magnetite nanoparticles, considered responsible for the III region, in the range 8-15 nm (for further details, see Paragraph 1 of the Supporting Information). This rough computation agrees with the literature data for iron oxides nanoparticles in the presence of a diamagnetic component.38,64


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The areas associated with iron in disordered and ordered magnetic phases have been calculated for the RT spectra. A 90:10 paramagnetic/ferrimagnetic ratio has been found for N481 and N409 (SA), while for the others a ratio of about 80:20 has been determined. These results are in agreement with the PXRD data that have shown a lower content of magnetite both for N481 and N409 samples. The doublet can be associated with iron ions dispersed within the glassy matrix and/or to crystalline phases that are paramagnetic at room temperature, i.e. biotite and/or pyroxenes and/or superparamagnetic magnetite nanoparticles. The experimental broad doublet (with isomer shift of 1.08-1.16 mm/s and quadrupole splitting of 1.96-2.20 mm/s) is the result of the almost complete overlapping of the subspectra of Fe2+ in different crystalline phases (biotite and pyroxenes70) and the doublet associated with Fe2+ with a wide quadrupole splitting distribution caused by structural disorder, i.e. iron ions dispersed within the glassy matrix. However, it should be considered that the presence of small amount of Fe3+ cannot be completely excluded. The most peculiar feature of the doublet is its asymmetry, measured as the ratio between the areas of the two peaks of the doublet (indicated as D21 in Table 2). In the literature, this feature has been revealed in other obsidian samples and it is commonly ascribed to overlapped symmetric subspectra of ferrous and ferric ions.2,4,13,22,27,30 However, in our case, due to the D21 values ranging between 0.65 and 0.85, the experimental data can be fitted only by an asymmetric doublet whereas the use of several symmetric subspectra of Fe2+ and Fe3+ did not lead to a reasonable interpretation of the data. Goldanskii-Karyagin effect (GKE), related to a different vibration amplitudes of the iron ions along one crystallographic axis with respect to the other ones, can be considered in our case the actual reason of the asymmetry due to the presence of the layered structure of the biotite.71 Indeed, biotite is a 2:1 sheet silicate made of TOT (tetrahedral-octahedral-tetrahedral) layers


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containing di- or trivalent cations (as Fe2+, Fe3+) six-fold coordinated by four oxygens and two hydroxyls sandwiched between two other sheets of silicon atoms four-fold coordinated by oxygen. These TOT sheets are weakly bound together by potassium ions and this structure may lead to a different vibration amplitude of iron ions along the axis perpendicular to the sheets and, as a consequence, the asymmetry can be justified in the light of the GKE. On the other hand, the GKE has been evidenced by other authors for other layered structures.72 An increase of the broadness and asymmetry of the doublet has been recorded in the 4 K Mössbauer spectrum of the sample N408 (SC) with respect to the RT one (Figure S10). Some authors interpreted these phenomena for paramagnetic compounds on the basis of the spin-lattice relaxation.73,74 In the literature, it is reported that the asymmetry may arise from the saturation or absorber thickness effect, preferred crystal orientation or texture effect, Goldanskii-Karyagin Effect (GKE) and paramagnetic relaxation phenomena.72 In the case study, all the possible explanations for the asymmetry can be excluded but Goldankii-Karagyn Effect, caused by the presence of biotite, that can be considered as the only explanation for biotite layered structure (for further details, see Paragraph 2 of the Supporting Information). In order to further support the occurrence of the GKE in obsidian, RT spectrum of a local biotite sample extracted from an amphibole-bearing migmatite75 (a metamorphic rock outcropping in the locality called Pittulongu in the north-eastern coast of Sardinia) has been recorded and is shown in Figure S11b (the associated PXRD pattern is reported in Figure S11a, showing only biotite and quartz as accessory phase). The hyperfine parameters are given in Table 2. In the literature, as already mentioned for the obsidian samples, the interpretation of the RT biotite spectrum has been reported by assuming the presence of three symmetric subspectra: one for octahedrally coordinated


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Fe2+ and two for octahedrally and tetrahedrally coordinated Fe3+.76 However, the common description of the biotite structure indicates the presence of a six-fold coordination for either ferric or ferrous ions. In our case, this spectrum can be well fitted by one asymmetric doublet associated with Fe2+ and a symmetric one due to Fe3+. Once again, the use of an asymmetric doublet appears to be necessary to interpret the experimental data as for the obsidian samples and in agreement with other authors77 even if they do not ascribe the asymmetry to the GKE. An increase of the broadness and asymmetry of the doublet has been found in the 4 K Mössbauer spectrum of biotite (Figure S11c) with respect to the RT one, as observed for obsidian. All these findings support the interpretation of the asymmetric Mössbauer doublet as mainly due to the GKE effect in biotite. 4. Transmission Electron Microscopy (TEM) In this complex framework, TEM analysis allowed to complete the picture on this natural material giving direct information on the mineralogical phases, morphology and on the dispersion of the crystalline phases onto the glassy matrix. Layered structures coexist with spheroidal nanoparticles and nanowires in all the analysed samples (Figure 4). Figure 4a reports a typical image of thin-layered structures for the sample N141. Selected Area Electron Diffraction shows both spots and rings suggesting the presence of at least two crystalline phases (Figure 4c). All the spots are ascribable to the biotite phase (PDF Card: 42-1339), a wellknown layered phase, while the two rings (Table S3) are both ascribable to magnetite in form of small particles, in agreement with PXRD, Mössbauer Spectroscopy and magnetic data. High Resolution TEM (Figure 4b) performed on the sample N141 permit to confirm the mineralogical composition of the layers being the lattice fringes identified as [132] planes of biotite. Perpendicularly to these thin layers darker crystalline nanofilaments or nanolayers (thickness of about 20 nm) are clearly visible in both bright field and dark field modes (Figure 4d and 4e). The


15


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Page 16 of 43

analysis of the Selected area Electron Diffraction image (Figure 4f, Table S3) allows assigning all the spots to the ferrosilite phase, suggesting once again the presence of a pyroxene in agreement with the PXRD and magnetic measurements. This is further supported by other observations through TEM analyses that evidenced, in rhyolitic glasses, similar morphologies ascribed to the class of the orthopyroxenes.7 An accurate analysis on several part of the sample N141, allows to evidence that small nanoparticles in the 5-12 nm size range are spread into the glassy matrix (Figure 4g). The SAED image (Figure 4h, Table S3) of the sample N141 shows the presence of haloes typical of the presence of polycrystalline magnetite made up of small nanoparticles. This is further confirmed by the HRTEM on the sample N141 showing a detail with two spheroidal particles oriented perpendicularly to the [311] and [220] typical for magnetite. These data are in agreement with the magnetic data that indirectly highlighted the presence of magnetic monodomain magnetite with a particle size distribution in the 8-15 nm range. The presence of magnetite nanoparticles dispersed into the glassy matrix can justify the exchange bias phenomena due to their possible contact with the antiferromagnetic phase evidenced by the magnetic measurements. TEM analysis on N141 (Figure 4 l, m, n) highlights the co-presence of magnetite nanoparticles together with the nanofilaments of pyroxene and biotite, suggesting that the antiferromagnetic phase could be the pyroxene, being biotite paramagnetic (Table S3). 5. Correlation of the magnetic properties with the mineralogical composition and the microstructure The combined use of PXRD and Mössbauer Spectroscopy has allowed to evidence the presence of crystalline phases, some of which have been already observed by other authors for obsidian from Monte Arci20,24,28,31,34,35 and other sources31,34,35.


16

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However, the correlation between the mineralogical composition and the associated magnetic properties has been never attempted to the best of our knowledge probably due to the intrinsic complexity of the material. Among the crystalline phases, the iron containing ones (biotite, pyroxenes and magnetite nanoparticles) can justify the three “magnetic regions” observed in the ZFC-FC curves and the temperature dependence of the M vs H curves. The region I of the ZFC curve with the typical paramagnetic behavior can be ascribed to the presence of both paramagnetic iron ions dispersed within the glassy matrix and biotite. This is further confirmed by the ZFC-FC curves measured on the same local biotite sample analyzed by 57

Fe Mössbauer Spectroscopy (Figure S12). As for obsidian, the ZFC-FC curves of biotite are

characterized only by a sharp increase of the magnetization at low temperature. The region II characterized by the discontinuity at about 45 K could be interpreted as a magnetic transition from an antiferromagnetic behavior to a paramagnetic one. In nature, different antiferromagnets show a Néel temperature in the range 30-50 K.78 For this reason, PXRD pattern of all the samples have been carefully rechecked. Among the antiferromagnetic phases, only the class of the pyroxenes, both orthopyroxenes and clinopyroxenes, seems to be compatible with the experimental PXRD profile, Mössbauer and TEM data. These evidences made us to hypothesize that a pyroxene would be the antiferromagnetic phase responsible for the feature of the II region. This hypothesis is supported by Wiedenmann et al. that for a synthetic sample of ferrosilite with formula 𝐹𝑒𝑆𝑖𝑂3 observed a Nèel temperature of 45 K79, and by other authors reporting for synthetic clinopyroxenes Néel temperatures of about 38 K80–83. Moreover, pure clinoferrosilite has been observed in natural samples, as obsidian from Kenya and other sources (California, Iceland, Yellowstone National Park), in association with some of the crystalline phases found also in Monte


17


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Page 18 of 43

Arci obsidian (anorthoclase rich in albite, low-cristobalite, magnetite, and biotite).84 From this dissertation, we can hypothesize the presence of a pyroxene with a composition close to 𝐹𝑒𝑆𝑖𝑂3 as responsible for the transition at about 45 K observed in the ZFC curve.85 PXRD,

57

Fe Mössbauer Spectroscopy and TEM data have confirmed also the presence of

nanostructured magnetite, hypothesized as a possible responsible for the III region, suggesting the presence of single-domain magnetite nanoparticles dispersed into the glassy matrix. Moreover, the evidences for exchange bias phenomena, although of small intensity, suggest that this ferrimagnetic phase (magnetite) can be in contact with the antiferromagnetic phase, forming magnetite/pyroxene interfaces. These findings are in agreement with the TEM observations and other studies from Befus et al. describing the microlite texture in obsidian and in particular the occurrence of magnetite as glomerocrysts associated with clinopyroxene and fayalite86 or the overgrowth of clinopyroxenes on Fe-Ti oxides.87 CONCLUSIONS This study demonstrates how the rational use of different consolidated techniques is strategic to get details that, as a whole, can give new insights even on complex and widely studied materials, as obsidian. This chemical physical approach can be considered as a helpful tool to complete the multidisciplinary overview on this material both for a basic understanding and for its possible applications as raw material.88 The composite nature of obsidian is here revealed for Sardinian obsidian as the coexistence of different magnetic phases responsible for a complex magnetic behavior: ferrimagnetism and superparamagnetism associated with magnetite nanoparticles together with antiferromagnetism of an iron-rich pyroxene and paramagnetism of biotite accompany the typical paramagnetism of Fe2+ ions dispersed in the glassy matrix. Almost all these common features have been visualized, known


18

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the mineralogical composition and the magnetic field dependence of the magnetization, through ZFC-FC protocols, that rarely are used to investigate natural materials. In this complex framework, exchange bias phenomena appear, due to the coupling of magnetite nanoparticles (ferrimagnetic phase) and iron-rich pyroxene (antiferromagnetic phase). This coupling phenomenon has been never observed in obsidian and other natural glasses, and rarely in nature and can give important information on the interfaces of the different crystalline phases in the glassy matrix. Some other details can be given by Mössbauer Spectroscopy measurements. The peculiar asymmetric doublet always present in the Mössbauer Spectra of Sardinian obsidian has been justified in terms of Goldankii-Karagyn Effect of biotite.


19


FIGURES

-2

-3

I

7.0x10

-3

ZFC FC 0

50

100

M (emu/g)

(c)

150

200

250

-3

1.0x10

-3

5.0x10

-4

0.0 0

50

100

150

-5

4.0x10

-5

3.0x10

-5

2.0x10

-5

1.0x10

-5

200

250

300

0.2

II

0.25

30 K

0.00 -0.25 -0.50 -0.75

(d)

5.0x10

T (K)

0.75 0.50

-5

0.0

(b)

2.0 1.5 I 1.0 0.5 5K 0.0 -0.5 -1.0 -1.5 -2.0 -40 -30 -20 -10 0 10 20 30 40

H (kOe)

1.5x10

300

T (K)

(a)

45 K

6.0x10

-1

-3

III

2.0x10

-3

MFC-MZFC -d(MFC-MZFC)/dT

-1

8.0x10

II

2.5x10

-3

-30 -20 -10 0

M (emu/g)

9.0x10

25 Oe

M (emu/g)

M (emu/g)

1.0x10

N141 (SB2)

N141 (SB2)

-2

MFC - MZFC (emu/g)

1.1x10

-d(MFC - MZFC)/dT (emu g K )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 43

(e)

III

300 K

0.0 -0.1 -0.2

10 20 30

H (kOe)

0.1

-20

-10

0

10

20

H (kOe)

Figure 1. ZFC-FC under a magnetic field of 25 Oe (a) and (M FC-MZFC) curves (b) of N141 obsidian. M vs H curves at 5 K (c), 30 K (d) and 300 K (e) are also shown for the same sample.


20

Page 21 of 43

N141 (SB2) 0.08

N141 (SB2)

5K

50

0.06

40

0.04 0.02

H (Oe) EB

M (emu/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.00 -0.02 -0.04

-0.08

0 0

-0.45 -0.30 -0.15 0.00 0.15 0.30 0.45

(a)

H (kOe)

20 10

ZFC FC (2T) FC (5T)

-0.06

30

10

(b)

20

30

40

50

60

T (K)

Figure 2. (a) Enlarged view of the central region of the hysteresis loops measured at T=5 K after cooling the sample N141 from T=300 K in a cooling field of 0, 2 and 5 T. (b) Exchange Bias Field (HEB) as a function of temperature.


21


Cu K

Ab Ab En Ab Ab Q Fs M En Bt Fs Fs Fs Bt M

10

20

30

40

 (°)

M M N408 N479 SC N405 N141 N128 SB2 N410 N226 N224 SB1 N109 N481 N429 SA N409

50

60

70

N408 N479 SC N405 N141

Intensity (a.u.)

Cb Ab Ab Fs

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 43

N128 SB2 N410 N226 N224 SB1 N109 N481 N429 SA N409

-12 -8

-4

0

4

8

12

Velocity (mm/s)

Figure 3. (a) XRD patterns of twelve samples (three for each geochemical site) of Monte Arci (Sardinia) obsidian. The most intense reflection for each crystalline phases is indicated by the bold label (Ab: Albite, Bt: Biotite, Cb: Cristobalite, En: Enstatite, Fs: ferrosilite, M: Magnetite, Q: Quartz). (b) RT Mössbauer spectra of twelve samples (three for each geochemical site) of Monte Arci (Sardinia) obsidian. The black arrow point the PXRD pattern and the Mössbauer spectrum for the sample N141 (SB2).


22

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. TEM (Bright Field, Dark Field and SAED) and HRTEM images of iron-containing phases on N141 sample. Bt, M and Fs identify biotite, magnetite and orthoferrosilite, respectively.


23


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Page 24 of 43

TABLES Table 1. Mineralogical composition obtained by Rietveld Analysis on twelve samples (three for each geochemical site) of Monte Arci (Sardinia) obsidian. Glassy matrix

Sample N408 (SC) N479 (SC) N405 (SC) N141 (SB2) N128 (SB2) N410 (SB2)* N226 (SB1)* N224 (SB1)

Ab

Bt

Cb

En

Fs

M

Q

-

NaAlSi3 K(Mg,Fe)3[AlSi3O10( O8 OH)2]

SiO2

MgSiO3 FeSiO3

Fe3O4

SiO2

%w/w

%w/w

%w/w

%w/w

%w/w

%w/w

%w/w

%w/w

5.8

82.4(4)

10.7(2)

1.1(1)

3.2(1)

0.8(1)

1.3(1)

0.4(1)

-

6.9

91.4(5)

3.2(2)

0.9(1)

2.0(1)

1.1(1)

0.8(1)

0.4(1)

-

6.0

91.1(5)

3.0(2)

0.9(1)

2.2(1)

1.3(1)

0.9(1)

0.4(1)

0.1(1)

5.2

93.6(4)

0.1(1)

0.9(1)

3.2(1)

1.0(1)

0.6(1)

0.4(1)

0.2(1)

6.2

92.3(5)

0.3(1)

1.1(1)

4.3(1)

0.7(1)

0.8(1)

0.3(1)

0.2(1)

5.5

93.5(4)

0.1(1)

0.7(1)

4.0(1)

0.5(1)

0.8(1)

0.3(1)

-

5.4

90.6(4)

1.0(1)

0.9(1)

4.2(1)

1.6(1)

0.8(1)

0.5(1)

0.2(1)

6.9

89.8(5)

1.2(1)

1.1(1)

4.0(1)

2.1(1)

0.7(1)

0.6(1)

-

Rw (%)


24

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

N109 (SB1) N481 (SA) N429 (SA)a) N409 (SA)a) a)


5.8

89.7(4)

1.3(1)

1.3(1)

3.9(1)

2.3(1)

0.7(1)

0.6(1)

-

5.4

92.1(4)

1.6(1)

0.9(1)

3.4(1)

0.7(1)

0.8(1)

0.2(1)

0.2(1)

5.9

92.1(4)

1.7(1)

0.9(1)

3.4(1)

0.7(1)

0.8(1)

0.2(1)

-

6.5

92.5(1)

2.0(1)

1.3(1)

2.7(1)

0.4(1)

0.5(1)

0.2(1)

0.2(1)

In this sample, traces of anorthite have been found.

Ab albite; Bt biotite; Cb: cristobalite; En: enstatite; Fs: orthoferrosilite; M: magnetite; Q: quartz.


25


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Page 26 of 43

Table 2. Mössbauer parameters of twelve Monte Arci samples at Room Temperature: Isomer Shift (δ), Quadrupole Splitting (ΔEQ), Hyperfine Field (BHf), Full-Width at Half-Maximum (FWHM), ratio between the areas of the two peaks of the doublet (D21), Relative Area (A) of the components. Last column list the interpretation for each subspectrum.

Sample

T (K)

4

N408 (SC)

BHf

FWHM

(mm/s) (mm/s) (T)

(mm/s)

1

1.28(1) 2.11(1) N/A

1.11(1)

0.43(2) 75

Paramagnetic Fe2+

2

0.47(1) 0.28(1) 51.9(2) 0.25(1)

10

Fe in Td sites (Fe3O4)

3

0.79(1) 0.61(1) 46.4(2) 0.63(1)

15

Fe in Oh sites (Fe3O4)

1

1.10(1) 2.16(1) N/A

0.80(1) 81

Paramagnetic Fe2+

Subsp.

293 2

N479 (SC)

N405 (SC)

δ

ΔEQ

0.55(1)

0.27(1) 0.07(1) 48.7(2) 0.30(1) 45.3(2) 0.48(1) 0.09(1)

3

0.66(1)

1

1.13(1) 2.15(1) N/A

0.58(1)

D21

A (%)

Interpretation

7


12


0.83(3) 82

Paramagnetic Fe2+

293 2

0.28(1)

48.9(2) 0.27(1) 0.08(1)

6


3

0.69(1)

44.9(2) 0.66(1) 0.07(1)

12


1

1.11(1) 2.10(1) N/A

0.78(2) 86

Paramagnetic Fe2+

0.67(1)

293 2

0.26(1)

48.6(2) 0.26(1) 0.02(1)

3


3

0.71(1)

45.1(2) 0.90(1) 0.05(1)

11



26

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1 N141 (SB2)

N128 (SB2)

N410 (SB2)

N226 (SB1)

N224 (SB1)

0.73(1)

0.65(2) 77

Paramagnetic Fe2+

293 2

0.26(1) 0.00(1) 49.0(1) 0.39(1)

5


3

0.66(1) 0.00(1) 46.0(1) 0.67(1)

18


1

1.09(1) 2.10(1) N/A

0.83(1) 80

Paramagnetic Fe2+

0.72(1)

293 2

0.32(1)

48.8(2) 0.40(1) 0.06(1)

9


3

0.69(1)

45.3(1) 0.47(1) 0.03(1)

11


1

1.07(1) 2.02(1) N/A

0.80(2) 83

Paramagnetic Fe2+

0.72(1)

293 2

0.29(1)

48.2(2) 0.18(1) 0.10(1)

4


3

0.61(1)

44.6(2) 0.57(1) 0.17(1)

13


1

1.14(1) 2.20(1) N/A

0.80(3) 80

Paramagnetic Fe2+

0.57(1)

293 2

0.26(1) 0.00(1) 49.0(2) 0.30(1)

3


3

0.66(1) 0.00(1) 46.0(1) 0.72(1)

17


1

1.13(1) 2.20(1) N/A

0.55(1)

0.84(2) 83

Paramagnetic Fe2+

0.27(1) 0.02(1) 48.5(1) 0.34(1)

10


7


293 2 3

N109

1.08(1) 1.96(1) N/A

293 1

0.60(1)

45.6(2) 0.25(1) 0.07(1)

1.14(1) 2.39(1) N/A

0.69(1)

0.85(1) 77

Paramagnetic Fe2+


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2

0.32(1)

48.6(1) 0.24(1) 0.06(1)

7


3

0.68(1)

45.1(1) 0.55(1) 0.02(1)

16


1

1.16(1) 2.09(1) N/A

0.69(1)

0.65(3) 91

Paramagnetic Fe2+

293 2

0.26(1) 0.00(1) 49(2)

0.54(1)

5


3

0.66(1) 0.00(1) 46(2)

0.42(1)

4


1

1.09(1) 2.14(1) N/A

0.71(1)

(SB1)

N481 (SA)

N429 (SA)

N409 (SA)

Page 28 of 43

293 2

0.29(1) 0.10(1) 48.9(1) 0.24(1) 45.3(1) 0.42(1) 0.12(1)

3

0.67(1)

1

1.09(1) 2.15(1) N/A

0.71(1)

0.81(2) 85

Paramagnetic Fe2+

5


10


0.82(2) 92

Paramagnetic Fe2+

293 2

0.32(1)

48.9(2) 0.27(1) 0.13(1)

3


3

0.65(1)

45.2(2) 0.42(1) 0.02(1)

5


1

1.11(1) 2.51(1) N/A

0.45(1)

0.72(1) 22

Paramagnetic Fe2+

2

0.46(1) 0.74(1) N/A

0.58(1)

78

Paramagnetic Fe3+

1

1.54(1) 3.15(1) N/A

2.38(1)

0.44(2) 95

Paramagnetic Fe2+

2

0.56(1) 0.74(1) N/A

0.80(1)

293 Biotite 4 5

Paramagnetic Fe3+

AUTHOR INFORMATION


28

Page 29 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Corresponding Author *Prof. Carla Cannas Dipartimento di Scienze Chimiche e Geologiche, Università di Cagliari, Cittadella Universitaria, Monserrato, 09042, Italy Phone number: (+39) 070/6754380 Email address: [email protected] ASSOCIATED CONTENT Supporting Information. Further details on the samples and other supplementary materials are provided in the Supporting Information file. In particular, the following material is reported: sampling locations, geographical coordinates for each sampling point and images of the twelve samples of Monte Arci (Sardinia) obsidian, supporting graphs and descriptions related to the magnetic measurements, supporting information related to the application of the Rietveld method to the XRD patterns, examples of curve fitting of the Mössbauer spectra and details on the interpretation of the data, supporting data collected on a local biotite sample and tables listing the assignments of the Electron Diffraction images. This material is available free of charge via the Internet at http://pubs.acs.org. ACKNOWLEDGMENT The use of the HR-TEM facilities of C.G.S. (Centro Grandi Strumenti, University of Cagliari) is gratefully acknowledged. Thanks are due to INPS (Istituto Nazionale di Previdenza Sociale) Gestione ex-INPDAP for the grant financing for Valentina Mameli and to AUSI and CREATE for


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Page 30 of 43

the grant of Andrea Ardu. We thank Prof. Franco Frau, PhD. Gabriele Cruciani and Prof. Jose A. De Toro for useful discussions and information. Fondazione Banco di Sardegna is also acknowledged for the financial support of the Department of Chemical and Geological Sciences of the University of Cagliari (PRID 2015). REFERENCES (1)

Pollard, A. M.; Heron, C. Archaeological Chemistry; Royal Society of Chemistry: Cambridge, 1996.

(2)

Ericson, J. E.; Makishima, A.; Mackenzie, J. D.; Berger, R. Chemical and Physical Properties of Obsidian: A Naturally Occuring Glass. J. Non. Cryst. Solids 1975, 17 (1), 129– 142.

(3)

Chavez-Rivas, F.; Régnard, J. R.; Chappert, J. Mössbauer Study of Natural Glasses : Lipari and Teotihuacan Obsidians. Le J. Phys. Colloq. 1980, 41 (C1), C1-275-C1-276.

(4)

Spiering, B.; Seifert, F. A. Iron in Silicate Glasses of Granitic Composition: A Mössbauer Spectroscopic Study. Contrib. to Mineral. Petrol. 1985, 90 (1), 63–73.

(5)

Chávez-Rivas, F.; Zamorano-Ulloa, R.; Galland, D.; Regnard, J. R.; Chappert, J. Ferro and Paramagnetic Resonance Studies of Natural Volcanic Glasses: Teotihuacan Obsidians. J. Appl. Phys. 1991, 70 (10), 5849–5851.

(6)

Okuno, M.; Iwatsuki, H.; Matsumoto, T. Structural Analysis of an Obsidian by X-Ray Diffraction Method. Eur. J. Mineral. 1996, 8 (1989), 1257–1264.

(7)

Sharp, T. G.; Stevenson, R. J.; Dingwell, D. B. Microlites and “nanolites” in Rhyolitic


30

Page 31 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Glass: Microstructural and Chemical Characterization. Bull. Volcanol. 1996, 56, 631–640. (8)

Tenorio, D.; Bosch, P.; Jimenez Reyes, M.; Bulbulian, S. Differences in Coloured Obsidians from Sierra de Pachuca, Mexico. J. Archaeol. Sci. 1998, 25 (3), 229–234.

(9)

Ma, C.; Gresh, J.; Rossman, G. R.; Ulmer, G. C.; Vicenzi, E. P. Micro-Analytical Study of the Optical Properties of Rainbow and Sheen Obsidians. Can. Mineral. 2001, 39 (1), 57– 71.

(10)

Zotov, N. Structure of Natural Volcanic Glasses: Diffraction versus Spectroscopic Perspective. J. Non. Cryst. Solids 2003, 323 (1–3), 1–6.

(11)

Kovács Kis, V.; Dódony, I.; Lábár, J. L. Amorphous and Partly Ordered Structures in SiO2 Rich Volcanic Glasses. An ED Study. Eur. J. Mineral. 2006, 18 (6), 745–752.

(12)

Ma, C.; Rossman, G. R.; Miller, J. A. The Origin of Color in “Fire” Obsidian. Can. Mineral. 2007, 45 (3), 551–557.

(13)

Rusakov, V. S.; Volovetskii, M. V.; Lukanin, O. A. Mössbauer Studies of Natural Glasses of Impact and Volcanic Origin. Moscow Univ. Phys. Bull. 2007, 62 (3), 187–192.

(14)

Ferk, A.; Leonhardt, R.; Hess, K. U.; Dingwell, D. B. Paleointensities on 8 Ka Obsidian from Mayor Island, New Zealand. Solid Earth 2011, 2 (2), 259–270.

(15)

Ferk, A.; Leonhardt, R.; Von Aulock, F. W.; Hess, K. U.; Dingwell, D. B. Paleointensities of Phonolitic Obsidian: Influence of Emplacement Rotations and Devitrification. J. Geophys. Res. Solid Earth 2011, 116 (12), 1–18.

(16)

Cañón-Tapia, E.; Cárdenas, K. Anisotropy of Magnetic Susceptibility and Magnetic


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 32 of 43

Properties of Obsidians: Volcanic Implications. Int. J. Earth Sci. 2012, 101 (3), 649–670. (17)

Tanaka, K.; Nemoto, N. Photoluminescence of Obsidian: A Particle-Dispersed Natural Glass. Phys. status solidi 2012, 9 (12), 2308–2311.

(18)

Waters, L. E.; Lange, R. A. Crystal-Poor, Multiply Saturated Rhyolites (Obsidians) from the Cascade and Mexican Arcs: Evidence of Degassing-Induced Crystallization of Phenocrysts. Contrib. to Mineral. Petrol. 2013, 166 (3), 731–754.

(19)

Rochette, P.; Gattacceca, J.; Devouard, B.; Moustard, F.; Bezaeva, N. S.; Cournède, C.; Scaillet, B. Magnetic Properties of Tektites and Other Related Impact Glasses. Earth Planet. Sci. Lett. 2015, 432, 381–390.

(20)

Aramu, F.; Maxia, V.; Serci, S.; Uras, I. Mössbauer Study of Mount Arci (Sardinia) Obsidian. Lett. Al Nuovo Cim. Ser. 2 1983, 36 (5), 102–104.

(21)

Schmidbauer, E.; Mosheim, E.; Semioschkina, N. Magnetization and 57Fe Mössbauer Study of Obsidians. Phys. Chem. Miner. 1986, 13 (4), 256–261.

(22)

Stewart, S. J.; Cernicchiaro, G.; Scorzelli, R. B.; Poupeau, G.; Acquafredda, P.; De Francesco, A. Magnetic Properties and 57Fe Mössbauer Spectroscopy of Mediterranean Prehistoric Obsidians for Provenance Studies. J. Non. Cryst. Solids 2003, 323 (1–3), 188– 192.

(23)

Duttine, M.; Scorzelli, R. B.; Cernicchiaro, G.; Poupeau, G.; Guillaume-Gentil, N. Magnetic Properties and Electron Spin Resonance of Ecuadorian Obsidians. Application to Provenance Research of Archeological Samples. J. Magn. Magn. Mater. 2008, 320 (14),


32

Page 33 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


136–138. (24)

Zanella, E.; Ferrara, E.; Bagnasco, L.; Ollà, A.; Lanza, R.; Beatrice, C. Magnetite GrainSize Analysis and Sourcing of Mediterranean Obsidians. J. Archaeol. Sci. 2012, 39 (5), 1493–1498.

(25)

Frahm, E.; Feinberg, J. M. From Flow to Quarry: Magnetic Properties of Obsidian and Changing the Scale of Archaeological Sourcing. J. Archaeol. Sci. 2013, 40 (10), 3706–3721.

(26)

Frahm, E.; Feinberg, J. M.; Schmidt-Magee, B. A.; Wilkinson, K.; Gasparyan, B.; Yeritsyan, B.; Karapetian, S.; Meliksetian, K.; Muth, M. J.; Adler, D. S. Sourcing Geochemically Identical Obsidian: Multiscalar Magnetic Variations in the Gutansar Volcanic Complex and Implications for Palaeolithic Research in Armenia. J. Archaeol. Sci. 2014, 47, 164–178.

(27)

Scorzelli, R. B.; Petrick, S.; Rossi, A. M.; Poupeau, G.; Bigazzi, G. Obsidian Archaeological Artefacts Provenance Studies in the Western Mediterranean Basin: An Approach by Mössbauer Spectroscopy and Electron Paramagnetic Resonance. Comptes Rendus l’Académie des Sci. - Ser. IIA - Earth Planet. Sci. 2001, 332 (12), 769–776.

(28)

Duttine, M.; Villeneuve, G.; Poupeau, G.; Rossi, a. M.; Scorzelli, R. B. Electron Spin Resonance of Fe3+ Ion in Obsidians from Mediterranean Islands. Application to Provenance Studies. J. Non. Cryst. Solids 2003, 323 (1–3), 193–199.

(29)

Longworth, G.; Warren, S. E. The Application of Mössbauer Spectroscopy to the Characterisation of Western Mediterranean Obsidian. J. Archaeol. Sci. 1979, 6 (2), 179– 193.


33


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(30)

Page 34 of 43

Bustamante, A.; Delgado, M.; Latini, R. M.; Bellido, A. V. B. Multivariate Analysis in Provenance Studies: Cerrillos Obsidians Case, Peru. Hyperfine Interact. 2007, 175 (1–3), 43–48.

(31)

Acquafredda, P.; Andriani, T.; Lorenzoni, S.; Zanettin, E. Chemical Characterization of Obsidians from Different Mediterranean Sources by Non-Destructive SEM-EDS Analytical Method. J. Archaeol. Sci. 1999, 26, 315–325.

(32)

Vásquez, C. A.; Nami, H. G.; Rapalini, A. E. Magnetic Sourcing of Obsidians in Southern South America: Some Successes and Doubts. J. Archaeol. Sci. 2001, 28 (6), 613–618.

(33)

Milleville, A.; Bellot-Gourlet, L.; Champagnon, B.; Santallier, D. La Micro-Spectroscopie Raman Pour L’étude Des Obsidiennes: Structure, Micro-Inclusions et Études de Provenance? Rev. d’Archéométrie 2003, 27 (1), 123–130.

(34)

Acquafredda, P.; Paglionico, A. SEM-EDS Microanalysis of Microphenocrysts of Mediterranean Obsidians: A Preliminary Approach to Source Discrimination. Eur. J. Mineral. 2004, 16 (3), 419–429.

(35)

Acquafredda, P.; Muntoni, I. M. Obsidian from Pulo Di Molfetta (Bari, Southern Italy): Provenance from Lipari and First Recognition of a Neolithic Sample from Monte Arci (Sardinia). J. Archaeol. Sci. 2008, 35 (4), 947–955.

(36)

Carter, E. A.; Hargreaves, M. D.; Kononenko, N.; Graham, I.; Edwards, H. G. M.; Swarbrick, B.; Torrence, R. Raman Spectroscopy Applied to Understanding Prehistoric Obsidian Trade in the Pacific Region. Vib. Spectrosc. 2009, 50 (1), 116–124.


34

Page 35 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(37)

Kelloway, S. J.; Kononenko, N.; Torrence, R.; Carter, E. A. Assessing the Viability of Portable Raman Spectroscopy for Determining the Geological Source of Obsidian. Vib. Spectrosc. 2010, 53 (1), 88–96.

(38)

Cannas, C.; Gatteschi, D.; Musinu, A.; Piccaluga, G.; Sangregorio, C. Structural and Magnetic Properties of Fe2O3 Nanoparticles Dispersed over a Silica Matrix. J. Phys. Chem. B 1998, 102 (40), 7721–7726.

(39)

Cannas, C.; Ardu, A.; Peddis, D.; Sangregorio, C.; Piccaluga, G.; Musinu, A. SurfactantAssisted Route to Fabricate CoFe2O4 Individual Nanoparticles and Spherical Assemblies. J. Colloid Interface Sci. 2010, 343 (2), 415–422.

(40)

Russo, R.; Granata, C.; Esposito, E.; Peddis, D.; Cannas, C.; Vettoliere, A. Nanoparticle Magnetization Measurements by a High Sensitive Nano-Superconducting Quantum Interference Device. Appl. Phys. Lett. 2012, 101 (12), 122601.

(41)

Mameli, V.; Musinu, A.; Ardu, A.; Ennas, G.; Peddis, D.; Niznansky, D.; Sangregorio, C.; Innocenti, C.; Thanh, N. T. K.; Cannas, C. Studying the Effect of Zn-Substitution on the Magnetic and Hyperthermic Properties of Cobalt Ferrite Nanoparticles. Nanoscale 2016, 8 (19), 10124–10137.

(42)

Lugliè, C.; Le Bourdonnec, F. X.; Poupeau, G.; Bohn, M.; Meloni, S.; Oddone, M.; Tanda, G. A Map of the Monte Arci (Sardinia Island, Western Mediterranean) Obsidian Primary to Secondary Sources. Implications for Neolithic Provenance Studies. Comptes Rendus Palevol 2006, 5 (8), 995–1003.

(43)

Lutterotti, L.; Matthies, S.; Wenk, H. R. MAUD: A Friendly Java Program for Material


35


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 36 of 43

Analysis Using Diffraction. IUCr Newsl. CPD 1999, 21, 14–15. (44)

Cannas, C.; Musinu, A.; Piccaluga, G.; Deidda, C.; Serra, F.; Bazzoni, M.; Enzo, S. Advances in the Structure and Microstructure Determination of Yttrium Silicates Using the Rietveld Method. J. Solid State Chem. 2005, 178 (5), 1526–1532.

(45)

Le Bail, A. Modelling the Silica Glass Structure by the Rietveld Method. J. Non. Cryst. Solids 1995, 183 (1–2), 39–42.

(46)

Ennas, G.; Marongiu, G.; Marras, S.; Piccaluga, G. Mechanochemical Route for the Synthesis of Cobalt Ferrite–Silica and Iron–Cobalt Alloy–Silica Nanocomposites. J. Nanoparticle Res. 2004, 6 (1), 99–105.

(47)

Dollase, W. A. Correction of Intensities for Preferred Orientation in Powder Diffractometry: Application of the March Model. J. Appl. Crystallogr. 1986, 19 (4), 267–272.

(48)

Chantrell, R. W.; El-Hilo, M.; O’Grady, K. Spin-Glass Behavior in a Fine Particle System. IEEE Trans. Magn. 1991, 27 (4), 3570–3578.

(49)

Hansen, M. F.; Mørup, S. Estimation of Blocking Temperatures from ZFC/FC Curves. J. Magn. Magn. Mater. 1999, 203 (1–3), 214–216.

(50)

Cannas, C.; Musinu, A.; Ardu, A.; Orrù, F.; Peddis, D.; Casu, M.; Sanna, R.; Angius, F.; Diaz, G.; Piccaluga, G. CoFe2O4 and CoFe2O4/SiO2 Core/Shell Nanoparticles: Magnetic and Spectroscopic Study. Chem. Mater. 2010, 22 (11), 3353–3361.

(51)

Suber, L.; Imperatori, P.; Mari, A.; Marchegiani, G.; Mansilla, M. V.; Fiorani, D.; Plunkett, W. R.; Rinaldi, D.; Cannas, C.; Ennas, G.; et al. Thermal Hysteresis of Morin Transition in


36

Page 37 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Hematite Particles. Phys. Chem. Chem. Phys. 2010, 12 (26), 6984. (52)

Winkler, E.; Zysler, R. D.; Fiorani, D. Surface and Magnetic Interaction Effects in Mn3O4 Nanoparticles. Phys. Rev. B 2004, 70 (17), 174406.

(53)

Suber, L.; Zysler, R.; Garcìa Santiago, A.; Fiorani, D.; Angiolini, M.; Montone, A.; Dormann, J. L. Size and Shape Effect on the Magnetic Properties of α-Fe2O3 Nanoparticles. Mater. Sci. Forum 1998, 269–272, 937–942.

(54)

Nogués, J.; Skumryev, V.; Sort, J.; Stoyanov, S.; Givord, D. Shell-Driven Magnetic Stability in Core-Shell Nanoparticles. Phys. Rev. Lett. 2006, 97 (15), 157203.

(55)

Estrader, M.; López-Ortega, A.; Estradé, S.; Golosovsky, I. V; Salazar-Alvarez, G.; Vasilakaki, M.; Trohidou, K. N.; Varela, M.; Stanley, D. C.; Sinko, M.; et al. Robust Antiferromagnetic Coupling in Hard-Soft Bi-Magnetic Core/shell Nanoparticles. Nat. Commun. 2013, 4, 2960.

(56)

Laureti, S.; Del Bianco, L.; Detlefs, B.; Agostinelli, E.; Foglietti, V.; Peddis, D.; Testa, A. M.; Varvaro, G.; Fiorani, D. Interface Exchange Coupling in a CoPt/NiO Bilayer. Thin Solid Films 2013, 543, 162–166.

(57)

Qureshi, M. T.; Baker, S. H.; Binns, C.; Roy, M.; Laureti, S.; Fiorani, D.; Peddis, D. Structure and Magnetic Properties of Fe Nanoparticles Embedded in a Cr Matrix. J. Magn. Magn. Mater. 2015, 378, 345–352.

(58)

Lottini, E.; López-Ortega, A.; Bertoni, G.; Turner, S.; Meledina, M.; Tendeloo, G. Van; de Julián Fernández, C.; Sangregorio, C. Strongly Exchange Coupled Core|Shell Nanoparticles


37


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 38 of 43

with High Magnetic Anisotropy: A Strategy toward Rare-Earth-Free Permanent Magnets. Chem. Mater. 2016, 28 (12), 4214–4222. (59)

Del Bianco, L.; Fiorani, D.; Testa, A.; Bonetti, E.; Signorini, L. Field-Cooling Dependence of Exchange Bias in a Granular System of Fe Nanoparticles Embedded in an Fe Oxide Matrix. Phys. Rev. B 2004, 70 (5), 52401.

(60)

Laureti, S.; Peddis, D.; Bianco, L. Del; Testa, A. M.; Varvaro, G.; Agostinelli, E.; Binns, C.; Baker, S. Exchange Bias and Magnetothermal Properties in Fe @ Mn Nanocomposites. J. Magn. Magn. Mater. 2012, 324, 3503–3507.

(61)

Domingo, N.; Testa, A. M.; Fiorani, D.; Binns, C.; Baker, S.; Tejada, J. Exchange Bias in Co Nanoparticles Embedded in an Mn Matrix. J. Magn. Magn. Mater. 2007, 316, 155–158.

(62)

Skumryev, V.; Stoyanov, S.; Zhang, Y.; Hadjipanayis, G.; Givord, D.; Nogués, J. Beating the Superparamagnetic Limit with Exchange Bias. Nature 2003, 423 (6942), 850–853.

(63)

Muscas, G.; Concas, G.; Cannas, C.; Musinu, A.; Ardu, A.; Orrù, F.; Fiorani, D.; Laureti, S.; Rinaldi, D.; Piccaluga, G.; et al. Magnetic Properties of Small Magnetite Nanocrystals. J. Phys. Chem. C 2013, 117 (44), 23378–23384.

(64)

Roca, A. G.; Morales, M. P.; O’Grady, K.; Serna, C. J. Structural and Magnetic Properties of Uniform Magnetite Nanoparticles Prepared by High Temperature Decomposition of Organic Precursors. Nanotechnology 2006, 17 (11), 2783–2788.

(65)

Murad, E.; Johnston, J. H. Iron Oxides and Oxyhydroxides. In Mössbauer Spectroscopy Applied to Inorganic Chemistry; Long, G., Ed.; Plenum Publ. Corp.: New York, 1987; pp


38

Page 39 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


507–583. (66)

Cara, C.; Musinu, A.; Mameli, V.; Ardu, A.; Niznansky, D.; Bursik, J.; Scorciapino, M. A.; Manzo, G.; Cannas, C. Dialkylamide as Both Capping Agent and Surfactant in a Direct Solvothermal Synthesis of Magnetite and Titania Nanoparticles. Cryst. Growth Des. 2015, 15 (5), 2364–2372.

(67)

Fantauzzi, M.; Pacella, A.; Atzei, D.; Gianfagna, A.; Andreozzi, G. B.; Rossi, A. Combined Use of X-Ray Photoelectron and Mössbauer Spectroscopic Techniques in the Analytical Characterization of Iron Oxidation State in Amphibole Asbestos. Anal. Bioanal. Chem. 2010, 396 (8), 2889–2898.

(68)

Jensen, S. D.; Shive, P. N. Cation Distribution in Sintered Titanomagnetites. J. Geophys. Res. 1973, 78 (35), 8474–8480.

(69)

Watt, J. P.; Leiper, W.; Ade-Hall, J. M.; Goble, D. F. Measurement of Fe3+/Fe2+ Ratios in Basaltic Class I Titanomagnetites Using the Mössbauer Effect. J. Geophys. Res. 1973, 78 (17), 3301–3309.

(70)

Stevens, J. G.; Khasanov, A. M.; Miller, J. W.; Pollak, H.; Li, Z. Mössbauer Mineral Handbook, Mössbauer.; Stevens, J. G., Khasanov, A. M., Miller, J. W., Pollak, H., Li, Z., Eds.; Mössbauer Effect Data Center: Asheville, 2005.

(71)

Goldanskii, V. I.; Makarov, E. F.; Suzdalev, I. P.; Vinogradov, I. A. Quantitative Test of the Vibrational Anisotropy Origin of the Asymmetry of Quadrupole Mössbauer Doublets. Phys. Rev. Lett. 1968, 20 (4), 137–140.


39


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(72)

Page 40 of 43

Das, S.; Ganguli, S.; Bhattacharya, M. Intensity Asymmetry in the Mössbauer Spectra of a Layered Cyanide. J. Phys. Condens. Matter 1990, 2 (34), 7209–7223.

(73)

Mørup, S. Mōssbauer Spectroscopy Studies of Relaxation Phenomena in Ultrafine Particles. In The Time Domain in Surface and Structural Dynamics; Springer Netherlands: Dordrecht, 1988; pp 309–320.

(74)

Bhargava, S. C.; Knudsen, J. E.; Mørup, S. Mössbauer Investigation of Spin-Lattice Relaxation of Paramagnetic Fe3+ Ions in NH4Al(SO4)2.12H2O. J. Phys. C Solid State Phys. 2001, 12 (14), 2879–2896.

(75)

Cruciani, G.; Franceschelli, M.; Jung, S.; Puxeddu, M.; Utzeri, D. Amphibole-Bearing Migmatites from the Variscan Belt of NE Sardinia, Italy: Partial Melting of Mid-Ordovician Igneous Sources. Lithos 2008, 105 (3–4), 208–224.

(76)

Martín-Hernández, F.; Hirt, A. M. The Anisotropy of Magnetic Susceptibility in Biotite, Muscovite and Chlorite Single Crystals. Tectonophysics 2003, 367 (1–2), 13–28.

(77)

Pollak, H.; De Coster, M.; Amelinckx, S. Mössbauer Effect in Biotite. Phys. status solidi 1962, 2 (12), 1653–1659.

(78)

Hunt, C. P.; Moskowitz, B. M.; Banerjee, S. K. Rock Physics & Phase Relations: A Handbook of Physical Constants. AGU Ref. Shelf 1995, 3, 189–204.

(79)

Wiedenmann, A.; Regnard, J.-R.; Fillion, G.; Hafner, S. S. Magnetic Properties and Magnetic Ordering of the Orthopyroxenes FexMg1-xSiO3. J. Phys. C Solid State Phys. 1986, 19, 3683–3695.


40

Page 41 of 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(80)

Coey, J. M. D.; Ghose, S. Magnetic Order in Hedenbergite: CaFeSi2O6. Solid State Commun. 1985, 53 (2), 143–145.

(81)

Baum, E.; Treutmann, W.; Lottermoser, W.; Amthauer, G. Magnetic Properties of the Clinopyroxenes Aegirine and Hedenbergite: A Magnetic Susceptibility Study on Single Crystals. Phys. Chem. Miner. 1997, 24 (4), 294–300.

(82)

Eeckhout, S. G.; de Grave, E.; Lougear, A.; Gerdan, M.; McCammon, C. A.; Trautwein, A. X.; Vochten, R. Magnetic Properties of Synthetic P21/c (Mg-Fe)SiO3 Clinopyroxenes as Observed from Their Low-Temperature Mössbauer Spectra and from SQUID Magnetization Measurements. Am. Mineral. 2001, 86 (9), 957–964.

(83)

Redhammer, G. J.; Roth, G.; Treutmann, W.; Paulus, W.; André, G.; Pietzonka, C.; Amthauer, G. Magnetic Ordering and Spin Structure in Ca-Bearing Clinopyroxenes CaM2+(Si, Ge)2O6, M=Fe, Ni, Co, Mn. J. Solid State Chem. 2008, 181 (11), 3163–3176.

(84)

Bowen, N. L. “Ferrosilite” as a Natural Mineral. Amer. J. Sci. 1935, 180 (180), 481.

(85)

Jaffe, H. W.; Robinson, P.; Tracy, R. J. Orthoferrosilite and Other Iron-Rich Pyroxenes in Microperthite Gneiss of the Mount Marcv Area. Adirondack Mountain. Am. Mineral. 1978, 63, 1116–1136.

(86)

Befus, K. S.; Zinke, R. W.; Jordan, J. S.; Manga, M.; Gardner, J. E. Pre-Eruptive Storage Conditions and Eruption Dynamics of a Small Rhyolite Dome: Douglas Knob, Yellowstone Volcanic Field, USA. Bull. Volcanol. 2014, 76 (3), 1–12.

(87)

Befus, K. S.; Manga, M.; Gardner, J. E.; Williams, M. Ascent and Emplacement Dynamics


41


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 42 of 43

of Obsidian Lavas Inferred from Microlite Textures. Bull. Volcanol. 2015, 77 (10). (88)

Belviso, C. EMT-Type Zeolite Synthesized from Obsidian. Microporous Mesoporous Mater. 2016, 226, 325–330.


42

Page 43 of 43


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