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Amphibole asbestos is related to multiple diseases, mainly those targeting the lungs. Asbestos-related malignancies can also be caused by non-regulated asbestiform minerals and some elongated mineral particles (EMPs). In particular, the role of nano- and micro-sized EMPs internalized by lung epithelial cells must be clarified. This is of major importance when considering that EMPs to which humans are exposed are likely a highly heterogeneous mix of different mineral types, shapes, and sizes. Here, we document that particles smaller than 4.54 µm in length and smaller than 0.89 µm in width (e.g., particles that do not fit the regulatory categories to be identified as asbestos) are easily internalized because of their specific dimensions, surface charge, and shape (mostly dictated by the aspect ratio L/w). Once internalized, these particles can be found in proximity to the cell nucleus, in vesicles, and in the cytoplasm. Examining the localization of particles in cells provides important information, which helps in determining the physicochemical environment found inside the biological compartment, thus allowing for a better comprehension of the mineralogical transformation that might happen after internalization by cells. [ABSTRACT FROM AUTHOR]

The existence of thermally-activated quasiparticles in amphiboles is an important issue, as amphiboles are among the main hydrous complex silicate minerals in the Earth's lithosphere. The amphibole structure consists of stripes of 6-membered TO4-rings sandwiching MO6 octahedral slabs. To elucidate the atomistic origin of the anomalous rock conductivity in subduction-wedge regions, we studied several Fe-containing amphiboles with diverse chemistry by using in situ, temperature-dependent, polarised Raman spectroscopy. The occurrence of resonance Raman scattering at high temperatures unambiguously reveal temperature-activated small polarons arising from the coupling between polar optical phonons and electron transitions within Fe2+O6 octahedra, independently of the amphibole chemical composition. The FeO6-related polarons coexist with delocalised H+; that is, at elevated temperatures Fe-bearing amphiboles are conductive and exhibit two types of charge carriers: electronic polarons with highly anisotropic mobility and H+ cations. The results from density-functional-theory calculations on the electron band structure for a selected amphibole compound with a relatively simple composition are in full agreement with experimental data. The polaron activation temperature, mobility, and polaron-dipole magnitude and alignment can be controlled by varying the mineral composition, which makes amphiboles attractive "geo-stripes" that can serve as mineral-inspired technology to design thermally-stable smart materials with anisotropic properties. [ABSTRACT FROM AUTHOR]

Amphibole asbestos is related to lung fibrosis and several types of lung tumors. The disease-triggering mechanisms still challenge our diagnostic capabilities and are still far from being fully understood. The literature focuses primarily on the role and formation of asbestos bodies in lung tissues, but there is a distinct lack of studies on amphibole particles that have been internalized by alveolar epithelial cells (AECs). These internalized particles may directly interact with the cell nucleus and the organelles, exerting a synergistic action with asbestos bodies (AB) from a different location. Here we document the near-atomic- to nano-scale transformations induced by, and taking place within, AECs of three distinct amphiboles (anthophyllite, grunerite, "amosite") with different Fe-content and morphologic features. We show that: (i) an Fe-rich layer is formed on the internalized particles, (ii) particle grain boundaries are transformed abiotically by the internal chemical environment of AECs and/or by a biologically induced mineralization mechanism, (iii) the Fe-rich material produced on the particle surface does not contain large amounts of P, in stark contrast to extracellular ABs, and (iv) the iron in the Fe-rich layer is derived from the particle itself. Internalized particles and ABs follow two distinct formation mechanisms reaching different physicochemical end-states. [ABSTRACT FROM AUTHOR]

We present the results of a comprehensive study linking the crystal‐chemical formulae of amphiboles, a series of extremely complex silicates with the general formula (AB2C5T8O22W2, C5 = M12M22M3) to variations in the peak positions, widths, and intensities of the Raman‐active modes. To this purpose, we have analyzed the Raman scattering generated by the framework vibrations (15–1,215 cm−1) and by the OH‐stretching modes (3,000–4,000 cm−1) of 44 samples, spanning all six major subgroups. We show that, in addition to the information that can be derived from the OH‐stretching range (Leissner et al., Am. Mineral. 2015, 100, 2682), further important features of the amphibole structure, composition, and cationic site population can be directly extracted from the framework Raman spectrum, namely, (a) the distinction between the monoclinic and orthorhombic symmetries; (b) the estimation of TAl content, when TAl > 0.5 apfu; (c) the estimation of CTi content, when CTi > 0.3 apfu; (d) the estimation of CLi content, when CLi > 0.3 apfu; (e) the detection of CAl, when CAl > 0.7 apfu; (f) an estimate of CMg; (g) the estimation of CFe3+ in the case of Na amphiboles; and (h) the estimation of the Fe2+ content at the M2 site in the case of Mg–Fe–Mn amphiboles. Additionally, we point out that the TO4‐ring‐breathing mode near 670 cm−1, which is commonly used to fingerprint various amphibole species, has to be handled with a great care, because it is sensitive to the site population at all crystallographic sites. [ABSTRACT FROM AUTHOR]

Vibrational spectroscopies (Fourier Transform Infra Red, FTIR, and Raman) are exceptionally valuable tools for the identification and crystal-chemical study of fibrous minerals, and asbestos amphiboles in particular. Raman spectroscopy has been widely applied in toxicological studies and thus a large corpus of reference data on regulated species is found in the literature. However, FTIR spectroscopy has been mostly used in crystal-chemical studies and very few data are found on asbestos amphiboles. This paper is intended to fill this gap. We report new FTIR data collected on a suite of well-characterized samples of the five regulated amphibole species: anthophyllite, amosite, and crocidolite, provided by the Union for International Cancer Control (UICC) Organization, and tremolite and actinolite, from two well-known occurrences. The data from these reference samples have been augmented by results from additional specimens to clarify some aspects of their spectroscopic features. We show that the FTIR spectra in both the OH-stretching region and in the lattice modes region can be effective for rapid identification of the asbestos type. [ABSTRACT FROM AUTHOR]

In this work, we investigate the oxidation behavior of a nearly end-member riebeckite, ideally Na2 ( Fe 3 2 + Fe 2 3 + ) $\begin{array}{} (\text{Fe}^{2+}_3\text{Fe}^{3+}_2) \end{array} $ Si8O22(OH)2, by using vibrational FTIR and Raman spectroscopies. Combining these results with previous studies performed on the same sample by single-crystal structure refinement and Mössbauer spectroscopy, we conclude that iron oxidation in riebeckite is a multi-step process. (1) In the ~523 K < T < 623 K temperature range, the O-H bond lengthens and both the electrons and the hydrogen cations delocalize. Raman analysis shows that this step is reversible upon cooling to room temperature. (2) In the 623 K < T < 723 K range, the kinetic energy increases so that the electrons can be ejected from the crystal; beyond 723 K an irreversible oxidation of Fe occurs that couples with irreversible changes in the SiO4 double-chains leading to a contraction of the unit-cell volume, i.e., to structural changes detectable at the long-range scale. (3) Beyond 823 K, the irreversible oxidation is completed and H+ ions are forced to leave the crystal bulk. Because of this multi-step process, the onset of the deprotonation process is detected at ~700 K by single-crystal XRD analysis of the unit-cell parameters, but starts at 623 K as indicated by Mössbauer spectroscopy on powders (and by changes in the cation distribution observed by structure refinement). Also, Raman scattering shows that the release of H+ from the crystal surface starts ~100 K before the complete deprotonation of the crystal bulk is witnessed by FTIR absorption. Hence, the oxidation of Fe starts at the crystal surface and induces electron and H+ migration from the crystal interior to the rim and thus subsequent oxidation through the crystal bulk. No deprotonation is observed by FTIR either in powders embedded in KBr or in crystals heated in N2 atmosphere, implying that the release of H+ needs surficial (atmospheric) oxygen to form H2O molecules. Fe2+ → Fe3+ oxidation produces a flux of electrons throughout the crystal matrix, which generates electrical conductivity across the amphibole. An important implication of this work, which might have interesting applications in material science, is that iron oxidation in riebeckite (and possibly in other Fe-rich silicates) is reversible in a given range of temperature. Also, this work shows that complex processes cannot be fully understood or even monitored accurately without using a proper combination of independent techniques. [ABSTRACT FROM AUTHOR]

Anomalous high-conductivity layers are typical of subduction zones, the largest recycling systems of the Earth. Understanding the mineral physics underlying the high conductivity of rocks has paramount implications for several planetary-scale processes, including global water cycling, earthquake activity, and arc magmatism. Here, by using in situ polarized Raman spectroscopy, we provide a direct proof for the development of anisotropic electron-phonon excitations (polarons) and delocalized H+ in riebeckite, a Fe-bearing sodic amphibole typical of blue-schist metamorphic facies. The activation of polarons starts at 500 K (227 °C) and is complete at 650 K (377 °C) under both reducing and oxidizing conditions. At higher temperatures external oxygen triggers the expulsion of H+ and e − from the crystal bulk. The temperature range observed for the development of charge carriers is in excellent agreement with the conductivity trends measured for riebeckite in previous studies, and nicely fits the temperatures for the development of high-conductivity layers in warm and cold subduction zones. The study directly demonstrates the activation of polarons at temperatures characteristic of convergent plate margins provides the atomic-scale picture whose macroscopic-scale expression is the anomalous conductivity measured in subduction zones. [Display omitted] [ABSTRACT FROM AUTHOR]

High-temperature Fourier transform infrared (HT-FTIR) spectroscopy was used to characterize the deprotonation process of synthetic potassic-ferro-richterite of composition A(K0.90Na0.07)B(Ca0.54Na1.46). Unpolarized single-crystal spectra were collected both in situ and on quenched samples, and heating experiments were conducted in air, at a rate of 10 °C/min. The room-T spectrum measured before annealing shows a main band at 3678 cm-1 and a minor band at 3622 cm-1; these are assigned to local configurations involving Fe2+ at M(1) M(1) M(3) and facing a filled and an empty alkali-site, respectively. At 400 °C, a new band grows at 3656 cm-1; this is the most intense feature in the pattern at 450 °C. At T ≥ 500 °C, all peaks decrease drastically in intensity, and finally disappear at T > 600 °C. The total absorbance measured in situ increases significantly in the 25 < T < 450 °C range, although the spectra collected on quenched samples show no OH loss in the same T range. This feature is consistent with an increase of the absorption coefficient (ε) with T, the reason for which is still unclear. However, this feature has significant implications for the quantitative use of FTIR data in HT experiments. Examination of the relevant OH-stretching bands shows that iron oxidation occurs preferentially at the M(1,3) sites associated with occupied A sites. The deprotonation temperature indicated by FTIR for single-crystals is around 100 °C higher that that obtained by HT-X-ray diffraction (XRD) on single crystal by , whereas that obtained by HT-XRD on powders is intermediate. This unexpected observation can be explained by considering that: (1) the iron oxidation process, which is coupled to deprotonation and is probed by XRD, occurs preferentially at the crystal surface where it is triggered by the availability of atmospheric oxygen; (2) the proton diffusion, probed by FTIR, is slower that the electron diffusion probed by XRD; thus, the temperature shift may be explained by a much longer escape path for H in single-crystals than in powders. These results suggest that possible effects due to crystals size should be carefully considered in HT experiments done on Fe-rich silicates. [ABSTRACT FROM AUTHOR]

Amphiboles caused cohorts of deaths in exposed workers, leading to some of the largest class actions in the industry. Once inhaled, these inorganic fibers are thought to be both chemically and morphologically toxic, and their biopersistence in the lungs over decades lead to progressive pathologies, mesothelioma, and asbestosis. However, this exceptionally long chronicity for human pathologies suggests that chemical toxicity is certainly low, suggesting that morphological parameters could be more relevant in the pathology. Here, we developed a 3D Raman/optical imaging methodology in vitro to characterize both morphological and chemical parameters of cell/fiber interactions. We determined that lung cells could vesiculate amphiboles with length below 5 μm or could embed those not exceeding 15 μm in their fibrous extracellular matrix. Lung cells can thus develop defense strategies for handling the biopersistence of inorganic species, which may thus have major impact for biosafety issues related to nanomaterials. [ABSTRACT FROM AUTHOR]

Actinolite and glaucophane are the principal amphiboles in greenschist- and blueschist-facies metamafic rocks, respectively, and constitute an important mineral pair for deducing the conditions of medium- and high-pressure metamorphism. Here we present the crystal-chemical properties of amphiboles synthesized along the tremolite--glaucophane join as an important starting point for the more chemically complex samples occurring in nature. Amphiboles were synthesized in 10 mol% increments at conditions ranging from 840 °C and 0.6 GPa for tremolite-rich to 750 °C and 2.5 GPa for glaucophane-rich amphiboles. The amphibole yields were generally high (~95 wt%), though minor quartz, pyroxene, and amorphous material (either glass or quenched solute) were often present. Electron microprobe analysis of the amphibole showed that deviations from the nominal or intended compositions occurred, with the observed compositions showing solid solution primarily toward the katophorite component and reaching a maximum near the middle of the join. Unit-cell dimensions showed a pronounced positive deviation from ideality, even after (linear) correction for the non-join components, suggesting a strong tendency toward exsolution. Single-crystal refinements of a couple of selected amphiboles confirmed the deviation from nominal composition and confirmed the presence of ANa, TAl, and AAl, the latter disordered between the M(2) and M(3) sites. Infrared spectra in the OH-stretching region were measured on samples that were heated to 250-350 °C to remove absorbed moisture. The spectra consist of a main band centered in the 3675-3660 cm-1 region and two minor absorptions on both sides of the dominant central peak, which are centered at 3720 and 3640 cm-1 and can be attributed to OH next to ANa and CAl, respectively. The main band is evidently composed of several overlapping components due to local arrangements of B cations typical of tremolite, CaCa, glaucophane, NaNa, and cummingtonite, MgMg. Examination of several intermediate amphiboles by both single-crystal XRD and by high-resolution TEM analysis could not identify evidence of reflections or ordered domains that would violate the C2/m symmetry of the end-member amphiboles. Comparing the compositions of the synthetic amphiboles from this study with winchite-rich amphiboles in nature shows that deviations from the tremolite-glaucophane join are common. The inability to make pure winchite or even winchite-rich amphiboles on the tremolite--glaucophane join suggests that this structure is unstable. [ABSTRACT FROM AUTHOR]

The thermal behavior of synthetic richterite ANaB(NaCa)CMg5TSi8O22(OH)2, crystallized at 800 °C and 0.35 GPa under hydrothermal conditions, was studied by serial powder diffraction experiments using synchrotron radiation between 123 and 873 K. The a, b, and β cell parameters show a non-linear behavior, whereas the c parameter shows a linear trend; values of the saturation temperature θs are 410(3), 215(2), and 300(2) K for a, b, and asinβ, respectively. The axial expansion pattern below room temperature is αb > αc > αa, whereas above room T it is αb > αa > αc, the difference being related to the different saturation temperatures of the individual cell parameters. The thermal expansion was modeled following the Debye approximation for the density-of-state of phonons; the refined parameters are V0 = 908.20 (0.04) ų, k = 1 (4), Q0 =32 (2) MJ, and the Debye temperature θD = 586(31) K. The non-linear behavior at low T is well described without systematic differences between the data and the model. The volume thermal expansion coefficient αV changes significantly with temperature, also at temperatures higher than room temperature. It is suggested that this may occur also in other amphiboles and pyroxenes, requiring critical re-examination of the available data. A comparison of the strain tensor for the thermal expansion between amphiboles and pyroxenes shows that in amphiboles the major deformation occurs onto the (010) plane, whereas in pyroxenes it occurs along the b axis. Moreover, the major deformation on (010) in Ca-bearing pyroxenes occurs along the bond of the M2 cation with the furthermost O3 atoms, whereas in compositionally related Ca-amphiboles (i.e., tremolite) it occurs in a direction rotated by 10-20° to a*, i.e., in a direction not corresponding to that of the M4-O5 bonds. It is proposed that the M4 polyhedron contributes less to the thermal deformation of amphibole than the M2 polyhedron contributes to the thermal deformation of pyroxene. [ABSTRACT FROM AUTHOR]

This paper reports the results of hydrothermal synthesis in the system Na2O-MgO-FeO-Fe2O3-SiO2-H2O, Four samples of stoichiometric magnesioriebeckite composition, ideally 〉Na2Mg3Fe23+Si8O22(OH)2, were run at 700-800 °C, 0.4 GPa, and redox conditions varying from NNO (Nickel-Nickel Oxide) to NNO + 2.3 log fO2. Powder XRD and SEM-EDX show a high (>85%) amphibole yield for all samples; however, in no case was the end-member composition attained. EMP analyses show that the amphiboles obtained deviate strongly from nominal stoichiometry toward magnesio-arfvedsonite [NaNa2Mg4Fe3+Si8O22(OH)2]. Powder XRD patterns were indexed in the space group C2/m; refined cell-parameters reflect variations in the amphibole composition, and the cell volume is correlated linearly with the A-site occupancy. Mössbauer spectra show that in all samples, Fe3+ is completely ordered at M2, whereas Fe2+ occurs at the M1, M3, and M4 sites. The Fe3+/Fe2+ ratio is a function of fO2: for increasing oxidation conditions, there is significant increase in M2Fe3+ and decrease in Fe2+, notably in M4Fe2+. Mössbauer spectra also show significant variation in M1Fe2+ and M3Fe2+ quadrupole splitting as a function of the Fe3+ content in the amphibole. IR spectra in the OH-stretching region show a well-resolved quadruplet at frequencies <3680 cm-1, assigned to octahedral M1,3(Mg, Fe2+)-OH-A〉 configurations, and a broad band consisting of four overlapping components related to M1,3(Mg, Fe2+) configurations associated with occupied A-sites. Quantitative evaluation of the relative band intensities suggests a linear increase of A-site occupancy with decreasing fO2 of synthesis. The composition of the amphiboles synthesized, can be best described by a combination of the C(Mg,Fe2+)1 B(Mg,Fe2+)1 CFe-13+ BNa-1 and the ANa1 C(Mg,Fe2+)1 A〉1 CFe-13+ exchange vectors. The experimental trend is in accord with the trend documented for natural amphiboles, and suggests that the amphibole composition can in fact be used to monitor changes in fO2 during crystallization. [ABSTRACT FROM AUTHOR]

This paper reports the results of hydrothermal synthesis in the system Na2O-MgO-FeO-Fe2O3-SiO2-H2O, Four samples of stoichiometric magnesioriebeckite composition, ideally 〉Na2Mg3Fe23+Si8O22(OH)2, were run at 700-800 °C, 0.4 GPa, and redox conditions varying from NNO (Nickel-Nickel Oxide) to NNO + 2.3 log fO2. Powder XRD and SEM-EDX show a high (>85%) amphibole yield for all samples; however, in no case was the end-member composition attained. EMP analyses show that the amphiboles obtained deviate strongly from nominal stoichiometry toward magnesio-arfvedsonite [NaNa2Mg4Fe3+Si8O22(OH)2]. Powder XRD patterns were indexed in the space group C2/m; refined cell-parameters reflect variations in the amphibole composition, and the cell volume is correlated linearly with the A-site occupancy. Mössbauer spectra show that in all samples, Fe3+ is completely ordered at M2, whereas Fe2+ occurs at the M1, M3, and M4 sites. The Fe3+/Fe2+ ratio is a function of fO2: for increasing oxidation conditions, there is significant increase in M2Fe3+ and decrease in Fe2+, notably in M4Fe2+. Mössbauer spectra also show significant variation in M1Fe2+ and M3Fe2+ quadrupole splitting as a function of the Fe3+ content in the amphibole. IR spectra in the OH-stretching region show a well-resolved quadruplet at frequencies <3680 cm-1, assigned to octahedral M1,3(Mg, Fe2+)-OH-A〉 configurations, and a broad band consisting of four overlapping components related to M1,3(Mg, Fe2+) configurations associated with occupied A-sites. Quantitative evaluation of the relative band intensities suggests a linear increase of A-site occupancy with decreasing fO2 of synthesis. The composition of the amphiboles synthesized, can be best described by a combination of the C(Mg,Fe2+)1 B(Mg,Fe2+)1 CFe-13+ BNa-1 and the ANa1 C exchange vectors. The experimental trend is in accord with the trend documented for natural amphiboles, and suggests that the amphibole composition can in fact be used to monitor changes in f2+)1 A〉1 CFe-13+ exchange vectors. The experimental trend is in accord with the trend documented for natural amphiboles, and suggests that the amphibole composition can in fact be used to monitor changes in fO2 during crystallization. [ABSTRACT FROM AUTHOR]

Synthetic NaNa2Mg5Si8O21(OH)3 is the first triclinic member of the amphibole group, and has a tripling of the unit cell in the b direction. The space group is C1 and the triple-b repeat gives Z = 6. The unit-cell parameters are: a = 9.883(2), b = 54.082(9), and c = 5.277(1) Å, α = 90.045(4)°, β = 103.068(3)°, γ = 89.960(4)°, and V = 2748(1) Å3. The crystal structure has been refined to R1 = 7.6 and wR2 = 16.7% for the 1835 reflections with Fo > 4σF and for 4832 supercell reflections in the 2θ range 2-25°, respectively. The structure is pseudo-monoclinic, but both the intensity distribution and refined model indicate space group C1. Compared with the common C2/m amphibole structure, the two halves of an I-beam unit are no longer mirror-related, and the overall structure can be rationalized in terms of two different types of I-beam occurring in the unit cell. The first (with multiplicity 2) is centrosymmetric, and the second (with multiplicity 4) is non-centrosymmetric. There are also significant displacements of the cations, especially at the M4 sites, from their corresponding locations in the C2/m structure. The correlated displacements of Na atoms at the M4 sites permit incorporation of excess protons in pseudo-tetrahedral cavities between two adjacent chains of tetrahedra belonging to different I-beams. Bond-valence calculations and crystal-chemical analysis suggest that excess protons are bonded to O atoms at the O4 sites, and are hydrogen bonded to O atoms at adjacent O2 sites. The infrared spectrum of the amphibole in the principal OH-stretching region has a triplet of sharp bands at 3740, 3727, and 3711 cm-1, which are assigned to the three independent "normal" O3-H groups in the triclinic structure. There is an additional intense and very broad absorption at 3430... [ABSTRACT FROM AUTHOR]

In the present work, we characterize the amphibole Na(NaMg)Mg5Si8O22 (OH)2 synthesized at 0.4 GPa and 750, 800, and 850 °C, and 0.5 GPa, 900 °C. Experiments at 800 and 900 °C yielded crystals suitable for single-crystal data collection. Structure refinement shows that synthetic Na(NaMg)Mg5Si8O22(OH)2 has P21/m symmetry at room T. The two non-equivalent tetrahedral double-chains differ in their degree of stretching and kinking. The infrared spectrum of synthetic Na(NaMg)Mg5Si8O22(OH), has two well-defined absorption bands at 3742 and 3715 cm-1 which can be assigned to 0-H bands associated with the two independent anion sites (03A and 03B) in the structure. The higher frequency band is assigned to the shorter 03B-H2 bond, and the lower frequency band is assigned to the longer 03A-H1 bond. The broader shape of the 3743 cm-1 band is consistent with a stronger interaction of the H2 atom with ANa, which is confirmed by structure refinement. Increasing T of synthesis causes a progressive departure from the ideal stoichiometry via the A〉1 BMg1,ANa-1,BNa-1 substitution, as confirmed by EMPA, structure refinement, and FTIR spectroscopy. [ABSTRACT FROM AUTHOR]

Deals with a study which described the crystal-chemical characterization of synthetic riebeckite, and demonstrated that complete exchange between sodium and lithium at the B-site in the amphibole structure can occur at relatively low temperature and pressure. Experimental methods; Results; Discussion.

Presents information on a study on the synthesis and characterization of amphiboles along the join pargasite-fluoro-pargasite. Methodology of the study; Results and discussion; Conclusion.

Presents results of the synthesis of amphiboles along the join K(NaCa)Mg5(Si7.4Ti0.6)O22(OH,F)2 from (OH)=2 to F=2 atoms per formula unit. Rietveld structure refinement; Spectroscopic studies.

Provides information on a study which presented an infrared analysis of short-range disorder of OH and F in monoclinic amphiboles. Methodology; Information on microprobe analysis of F content; Interpretation of the spectra.

Presents the results in which amphiboles were synthesized along the join potassium-richterite (Kr)-tremolite (Tr). Amphiboles characterized by Rietveld structure refinement, infrared spectroscopy, and electron-microphobe analysis.

Examines metal occupancies in synthetic monoclinic amphiboles. Characterization of the structural variations of the mineral using the Rietveld method; Techniques used for deriving precise band intensities of the metals; Variations in molar absorptivity with frequency.

A new approach to extract accurate information on the Fe oxidation state has been tested on three different Fe-rich amphiboles annealed at 194–520 °C. The method is based on the analysis of the pre-edge structure of the X-ray absorption spectra at the Fe-K edge. The pre-edge band is deconvolved into four Gaussian components where the integrated intensities of the pairs of lower- and higher-energy bands are related to the ferrous to ferric ion ratio. These Fe3+/Fe tot ratios have been compared with those obtained with independent techniques (X-ray diffraction and Mossbauer spectroscopy) on the same samples. The experimental data allowed establishing a calibration curve that is in good agreement with a recent statistical analysis based on spectroscopic data for the same type of minerals. The method could be extended to the analysis of other complex systems containing both Fe3+ and Fe2+ in octahedral coordination or to study the dynamics of iron under non-ambient conditions. • Extraction of the Fe3+/Fe tot ratio from the pre-edge structure at the Fe K-edge. • Fitting of the pre-edge with 4 Gaussians representative of ferric and ferrous ion. • Calibration line combining the pre-edge analysis and Mössbauer spectroscopy data. • Method suitable to investigate Fe dynamics in complex systems such as amphiboles. [ABSTRACT FROM AUTHOR]

Shows that the nontremolite components in tremolite are not randomly distributed throughout the structure but show extreme short-range order. Assignment of the component bands in the infrared spectrum of tremolite containing alpha(Na,K); Crystal-chemical couplings within the amphibole structure; Configurational entropy; Activity models for amphiboles.

All six minerals defined as "asbestos" by the existing regulation on asbestos hazard, i.e., actinolite, tremolite, anthophyllite, crocidolite and amosite amphiboles, and the serpentine-group mineral chrysotile are typical constituents of mafic and ultramafic magmatic rocks of ophiolitic sequences. However, little is known about the presence and distribution of naturally occurring asbestos (NOA) in plutonic felsic rocks. The Isadalu magmatic complex outcropping in central Sardinia and belonging to the post-variscan Permian volcanic cycle, is described here as an interesting occurrence of fibrous amphiboles in granitoid rocks. Field work and collected mineralogical/petrological data show that NOA fibers from the Isadalu complex belong compositionally to the actinolite-tremolite series. They were generated by metasomatic growth on pristine magmatic hornblende, at ca. 470 °C at 1 kbar, during sodic-calcic hydrothermal alteration. In terms of environmental hazard, the Isadalu complex represents a high-value case study, since the actinolite-bearing felsic rocks outcrop in a strongly anthropized area. Here, towns with local and regional strategic infrastructures (dams, pipes, hydroelectric power plants, water supply, roads) have been developed since the last century, also using the granitoid asbestos-rich stones. The aim of this study is to demonstrate that NOA and relative hazard are not univocally connected to a restricted typology of rocks. This result should be taken into account in any future work, procedure or regulation defining asbestos occurrences in natural environments. [ABSTRACT FROM AUTHOR]

This work reports the crystal-chemical characterization of Mn-rich amphiboles from the Grenville Marble of the Arnold mine, Fowler, St. Lawrence Co., New York (U.S.A.), which were previously described by Benimoff et al. (1991) as "manganoan silicic edenite." According to the new nomenclature scheme for monoclinic amphiboles (Leake et al. 2004) the ideal composition of reference, ANaB(CaMn) CMg5 T(Si7Al)O22(OH)2 with Ca > 1 apfu, is an end-member of the newly defined Group 5, and is named parvo-mangano-edenite. Re-examination of the original rock specimen showed significant inter- and intra- crystalline compositional variations, which can be expressed by theANa-1TAl-1A〉1TSi1 and BMn2 BCa-2 exchange vectors. The first vector leads to parvo-manganotremolite, ideally A〉B(CaMn)CMg5 T with Ca > 1. The second mechanism was never found to reach Mn dominance; however, crystal-chemical analysis does not provide any evidence of structural limits, and thus the magno-calcic counterparts of the Group 5 amphiboles of this work may occur in similar but Mn-richer genetic environments. The presence of Mn at the B site helps to stabilize the charge arrangement of edenite. The parvo-mangano-edenite crystal with composition closest to the end-member, i.e., 8O22(OH)2 with Ca > 1. The second mechanism was never found to reach Mn dominance; however, crystal-chemical analysis does not provide any evidence of structural limits, and thus the magno-calcic counterparts of the Group 5 amphiboles of this work may occur in similar but Mn-richer genetic environments. The presence of Mn at the B site helps to stabilize the charge arrangement of edenite. The parvo-mangano-edenite crystal with composition closest to the end-member, i.e., A(Na0.74 K0.02)B(Ca1.27Mn0.73)C(Mg4.51Mn0.282+Fe0.052+Fe0.033+Al0.12Ti0.01)T(Si7.07Al0.93)O22(OH)2, has a = 9.8260(5), b = 18.0487(9), c = 5.2840(4) Å, β = 104.55(1)°, V = 907.1 ų (Z = 2); the calculated density is 3.11 g/cm³. The parvo-mangano tremolite crystal, with composition A(Na0.44K0.01)B(Ca1.13Mn0.83Na0.04)C(Mg 4.69Mn0.212+Fe0.032+Fe0.013+Al0.06)T(Si7.52Al0.48)O22, respectively. FTIR spectroscopy indicates extensive short-range-order of cations in these amphiboles. [ABSTRACT FROM AUTHOR]2, has a = 9.7807(5), b = 18.0548(9), c = 5.2928(4) Å, β = 104.19(1)°, V = 906.1 ų (Z = 2); the calculated density is 3.08 g/cm³. The different compositions are virtually indistinguishable under the optical microscope, but can be identified by a measure of their unit-cell parameters. The single-crystal FTIR spectrum of parvo-mangano-edenite in the OH-stretching region shows two main absorptions at 3711 and 3671 cm-1, plus shoulders at 3695, 3660, and 3641 cm-1, respectively. FTIR spectroscopy indicates extensive short-range-order of cations in these amphiboles. [ABSTRACT FROM AUTHOR]

Potassic-jeanlouisite, ideally K(NaCa)(Mg4Ti)Si8O22O2, is the first characterised species of oxo amphibole related to the sodium–calcium group, and derives from potassic richterite via the coupled exchange CMg–1W ${\rm OH}_{{\rm \ndash 2}}^{\ndash}{} ^{\rm C}{\rm Ti}_1^{{\rm 4 +}} {} ^{\rm W}\!{\rm O}_2^{2\ndash} $. The mineral and the mineral name were approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification, IMA2018-050. Potassic-jeanlouisite was found in a specimen of leucite which is found in the lava layers, collected in the active gravel quarry on Zirkle Mesa, Leucite Hills, Wyoming, USA. It occurs as pale yellow to colourless acicular crystals in small vugs. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: A(K0.84Na0.16)Σ1.00B(Ca0.93Na1.02Mg0.04 ${\rm Mn}_{{\rm 0}{\rm. 01}}^{2 +} $)Σ2.00C(Mg3.85 ${\rm Fe}_{{\rm 0}{\rm. 16}}^{2 +} $ Ni0.01 ${\rm Fe}_{{\rm 0}{\rm. 33}}^{3 +} {\rm V}_{{\rm 0}{\rm. 01}}^{3 +} $ Ti0.65)Σ5.01T(Si7.76Al0.09Ti0.15)Σ8.00O22W[O1.53F0.47]Σ2.00. The holotype crystal is biaxial (–), with α = 1.674(2), β = 1.688(2), γ = 1.698(2), 2Vmeas. = 79(1)° and 2Vcalc. = 79.8°. The unit-cell parameters are a = 9.9372(10), b = 18.010(2), c = 5.2808(5) Å, β = 104.955(2)°, V = 913.1(2) Å3, Z = 2 and space group C 2/ m. The strongest eight reflections in the powder X-ray pattern [ d values (in Å) (I) (hkl)] are: 2.703 (100) (151); 3.380 (87) (131); 2.541 (80) ($\bar 2$ 02); 3.151 (70) (310); 3.284 (68) (240); 8.472 (59) (110); 2.587 (52) (061); 2.945 (50) (221, $\bar 1$ 51). [ABSTRACT FROM AUTHOR]

The crystal structures of six gem-quality pargasites and fluoro-pargasites from Mogok, Myanmar, space group C 2/ m , Z = 2, have been refined to R 1 indices of 2.20–2.90% using Mo K α X-radiation. The unit formulae were calculated from the results of electron-microprobe analysis, and were used with the refined site-scattering values and the observed mean bond lengths to assign site populations. T Al occurs at both the T (1) and T (2) sites but is strongly ordered at T (1). [6]Al is partly disordered over the M (2) and M (3) sites but does not occur at the M (1) site. A Na is split between the A (2) and A (m) sites and K occurs at the A (m) site. The infrared spectra in the principal OH-stretching region were measured and the fine structure was fit to component bands. The component bands were assigned to short-range ion arrangements over the configuration symbol M (1) M (1) M (3)–O(3)– A –O(3): T (1) T (1) using the refined site-populations and the expected frequencies from previously assigned spectra in more simple amphibole compositions, and correspond to the local arrangements: (1) MgMgMg–OH–Na–OH:SiAl; (2) MgMgMg–OH–Na–F:SiAl; (3) MgMgAl–OH–Na–OH:SiAl and (4) MgMgAl–OH–Na–F:SiAl. [ABSTRACT FROM AUTHOR]