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Aggregates and rocks from quarries located in metropolitan France and New Caledonia, all likely to contain asbestiform amphiboles, were analysed by a routine laboratory (AD-LAB). Morphological observations were made using transmission electron microscopy and chemical analyses were obtained with energy dispersive X-ray spectroscopy. The chemical analyses obtained from amphiboles were treated in such a way that they could be plotted in a diagram (Si apfu versus Mg/Mg+Fe2+). The points corresponding to analysed particles, classified as asbestos, define a broader compositional domain than that corresponding to the compositional areas of actinolite and tremolite. The creation of two new domains is proposed. Samples of basic metavolcanics and amphibolites collected by the Geological and Mining Research Bureau (BRGM) in different quarries of the Armorican Massif and the Massif Central containing calcic amphibole fibres have been the subject of polarized light microscope and electron microprobe analyses. The representative points of the spot chemical analyses performed on the very fine and ultrafine fibres are contained in the range defined previously. The diagram that has been determined from chemical analyses coupled with morphological and dimensional observations can help the "routine laboratories" to better characterise asbestiform calcic amphiboles, but it also allows comparisons with geological observations. [ABSTRACT FROM AUTHOR]

Abstract The issue of Elongated Mineral Particles (EMP) in building materials has been revealed during roadworks in 2013 in France. In fact, road coating aggregates are made of specific rock gravels that can contain Naturally Occurring Asbestos (NOA), which is mainly actinolite. The legislation refers to six regulatory asbestos, that consist in asbestiform habitus of the six minerals. The current technical standard is not adapted for analyzing natural material, as it cannot distinguish the asbestiform fibers and the cleavage fragments fibers. Therefore, the Eichrom Laboratories developed an internal method for analyzing rock gravel and identifying the different kind of EMP. This analytical method is based on an accurate sample preparation and three techniques at different resolutions: a petrological analysis with a stereomicroscope, a mineralogical analysis with a Polarized Light Microscope (PLM) and structural and with a Transmission Electronic Microscope (TEM). This innovative procedure is reinforced by the expertise of geologists, which is not necessary for the manufactured products. Putting the process in a national standard is essential for result homogenization of the asbestos testing laboratories. Highlights • The grinding allows distinguishing the different kind of fibers. • A quantitative analysis of diffraction and chemical composition is necessary. • A quantitative analysis of elongated mineral particles would be reliable. [ABSTRACT FROM AUTHOR]

The Kadui blueschist is located in the central section of Yarlung Zangbo suture zone (YZSZ), southern Tibet, and has been subjected to the subduction of the Neo-Tethyan Ocean below the Asian Plate and provides important clues for better understanding the evolution of the India-Asia convergence zone. In this paper, the systematical petrographic and mineral chemical studies were carried out on the Kadui blueschist, which reveal a mineral assemblage of sodic amphibole, chlorite, epidote, albite and quartz with accessory minerals of titanite, calcite and zircon. Electron microprobe analyses demonstrate that amphibole shows zoned from actinolite core to ferrowinchite/riebeckite rim composition indicating that the sodic amphibole has formed during a prograde metamorphic event. The protolith of the blueschist is an intermediate-basic pyroclastic rock. The calculated pseudosection indicates a clockwise P-T path and constrains peak metamorphic conditions of about 5.9 kbar at 345 °C. This condition is transitional between pumpellyite-actinolite, greenschist and blueschist facies with a burial depth of 20-22 km and a thermal gradient of 15-16 °C/km. This thermal gradient belongs to high pressure intermediate P/T facies series and is possibly related to a warm subduction setting of young oceanic slabs. Our new findings indicate that the Kadui blueschist in the central part of YZSZ experienced a rapid subduction and exhumation process as a response to a northward subduction of the Neo-Tethyan oceanic lithosphere during the initial India-Asia collision stage. [ABSTRACT FROM AUTHOR]

Raman and infrared spectroscopy are fast, simple and useful methods of identifying and distinguishing between different rock samples, which often originate from different sources. We analyzed nephrite samples from Polish deposits (Złoty Stok in the Sudetes and Jordanów Śląski in the Fore-Sudetic Block). Studied nephrites amphiboles, with the general formula (Ca 2 (Mg,Fe) 5 Si 8 O 22 (OH) 2 ), magnesium and iron contents, in terms of Fe/(Fe+Mg) per formula unit, are as follows: Jordanów Śląski (0.06–0.10), Złoty Stok type 1 (0.10–0.20) and Złoty Stok type 2 (0.04–0.18). Our spectroscopic study is consistent with results of previous petrographic microscopy, scanning electron microscopy and chemical composition of constituting minerals, measured by the electron microprobe; which methods were applied to the same nephrite deposits. Results of Jordanów and Złoty Stok nephrites studies were compared with data available in literature, which confirmed petrographic composition of studied samples. In addition, in case of actinolite nephrite samples (Fe/(Fe+Mg) > 0.10), qualification of the studied minerals to actinolite with content of Fe ion below 15% and 30% in sample from Jordanów Śląski and Złoty Stok, respectively, is possible based solely on applied spectroscopic methods. Spectroscopic studies also allowed to note the relationship between the obtained results and the genetic origin (serpentinite-related or dolomite-related) of the studied nephrites. Findings confirmed that spectroscopic methods are not only applicable and useful, but, which is very important in gemological and archaeometric practice, also non-destructive. [ABSTRACT FROM AUTHOR]

A facile one-pot method through controlled nucleation and release of reactive nutrient species by using bulk silicon dioxide as the Si source and seeds as liberated nuclei was reported for the fabrication of hierarchical ZSM-5 zeolites. This ZSM-5 aggregation (ZSM-5-B) was hierarchically constructed by many flaky ZSM-5 crystals. High methane conversion, high selectivity of aromatics and excellent anti-coking stability were achieved in the catalytic methane dehydroaromatization reaction (MDA) as a model reaction using the Mo-modified ZSM-5-B catalyst. Structure-properties relevance studies indicated the synergistic integration of the suitable acidity, higher external surface and hierarchical porosity contributed to the largely improved MDA catalytic performance. The work demonstrates a much simpler and more economical route for practical application of hierarchical zeolite. [ABSTRACT FROM AUTHOR]

Subduction megathrusts below the land Moho slip at either steady creep or episodic slow slip events (SSEs). However, deformation styles and mechanisms responsible for aseismic megathrust slip remain unknown. We examined the subduction mélange in Kyushu, Japan, which consists of ultramafic, mafic, and sedimentary rocks. The mélange deformed at ∼470 °C under epidote-amphibolite facies condition, comparable to the inferred conditions of SSEs near the mantle wedge corner in the Nankai subduction zone. Subduction-related viscous shear in the mélange was concentrated into antigorite serpentinite and ultramafic schist mainly composed of chlorite and fine-grained actinolite, which is characterized by anastomosing scaly foliations and S C fabric. The mixing of mafic and ultramafic rocks in the mélange induced metasomatic reactions, resulting in the release of water from metasomatized mafic rock and the production of fine-grained actinolite in ultramafic schist. The fine-grained metasomatic actinolite exhibits chemical zoning of aluminum and truncation of the zoning parallel to S surface through dissolution-precipitation creep. Water released by metasomatic reactions may assist the dissolution-precipitation creep. Rheological analysis indicates that the dissolution-precipitation creep of fine-grained actinolite in ultramafic schist accommodated plate convergence and SSEs at shear stresses of 0.3–5 MPa and 10–40 MPa, respectively, whereas antigorite serpentinite can accommodate slow slip rates at shear stresses of ≤43–94 MPa, much higher than inferred shear stresses during SSEs in active subduction zones. The down-dip limit of the metasomatic reactions, determined from the stable condition of metasomatic actinolite in the ultramafic schist, was ∼40–50 km depth, comparable to the lower limit of the SSEs region in the Nankai subduction zone. We suggest that while antigorite serpentinite only accommodated aseismic creep, dissolution-precipitation creep of metasomatic actinolite in weaker ultramafic schist can host more diverse slip behavior including aseismic creep and SSEs. The metasomatic reaction between mafic and ultramafic rocks at the slab-mantle interface is potentially one of the factors controlling the downdip limit of SSEs below the land Moho. • Mélange deformation was concentrated into serpentinite and ultramafic schist. • Metasomatic reactions produce fine-grained actinolite in ultramafic schist. • Metasomatic reactions weaken ultramafic schist by promoting pressure solution creep. • Pressure solution creep of metasomatic actinolite can facilitate megathrust slip. • Metasomatic reaction may control downdip limit of slow slip event. [ABSTRACT FROM AUTHOR]

The paper reports original thermochemical data on six natural amphibole samples of different composition. The data were obtained by high-temperature melt solution calorimetry in a Tian-Calvet microcalorometer and include the enthalpies of formation from elements for actinolite Ca(MgFeAl)[SiO](OH)(-12024 ± 13 kJ/mol) and Ca(MgFeFe)[SiAlO](OH), (-11462 ± 18 kJ/mol), and NaCa(MgFeFe)[SiAlO](OH) (-11588 ± 14 kJ/mol); for pargasite NaKCa-(MgFeAl)[SiAlO](OH) (-12316 ± 10 kJ/mol) and NaKCa(MgFeAl) [SiAlO](OH) (-12 223 ± 9 kJ/mol); and for hastingsite NaKCa(MgFeFeAl) [SiAlO](OH) (-10909 ± 11 kJ/mol). The standard entropy, enthalpy, and Gibbs free energy of formation are estimated for amphiboles of theoretical composition: end members and intermediate members of the isomorphic series tremolite-ferroactinolite, edenite-ferroedenite, pargasite-ferropargasite, and hastingsite. [ABSTRACT FROM AUTHOR]

Garnet-bearing mafic granulites and amphibolites from the Hongliuxia area of the southern Dunhuang orogenic belt, northwestern China, commonly occur as lenses or boudinages enclosed within metapelite or marble, which represent the block-in-matrix feature typical of orogenic mélange. Three to four generations of metamorphic mineral assemblages are preserved in these rocks. In the high-pressure amphibolites, prograde mineral assemblages (M1) occur as inclusions (hornblende + plagioclase + quartz ± chlorite ± epidote ± ilmenite) preserved within garnet porphyroblasts, and formed at 550–590 °C and 7.7–9.2 kbar based on geothermobarometry. The metamorphic peak mineral assemblages (M2) are composed of garnet + hornblende + plagioclase + quartz + clinopyroxene, as well as titanite + zircon + rutile + apatite as accessory minerals in the matrix, and are estimated to have formed at 640–720 °C and 14.1–16.0 kbar. The first retrograde assemblages (M3) are characterized by “white-eye socket” symplectites (hornblende + plagioclase + quartz ± biotite ± epidote ± magnetite) rimming garnet porphyroblasts, which formed at the expense of the garnet rims and adjacent matrix minerals during the decompression stage under P – T conditions of 610–630 °C and 5.6–11.8 kbar. The second retrograde assemblages (M4) are intergrowths of actinolite and worm-like quartz produced by the breakdown of the matrix hornblendes, and formed under P – T conditions of ∼490 °C and ∼2.8 kbar. For the high-pressure mafic granulites, the prograde assemblages (M1) are represented by plagioclase + quartz preserved within the garnet porphyroblasts. The metamorphic peak assemblages (M2) are garnet + matrix minerals (clinopyroxene + plagioclase + quartz + hornblende + rutile + zircon) and were estimated to have formed at ∼680 °C and ∼15.4 kbar. The retrograde assemblages (M3) are characterized by fine-grained patches of hornblende + plagioclase + quartz rimming the garnet porphyroblasts, as well as hornblende rimming clinopyroxene in the matrix, and were inferred to have formed at ∼620 °C and ∼4.2 kbar. For the metapelitic gneiss, the metamorphic peak assemblages are the garnet porphyroblasts plus the matrix minerals (biotite + plagioclase + quartz + ilmenite + zircon), which were estimated to have formed at ∼630 °C and ∼8.9 kbar. The mafic granulites and amphibolites record fairly similar clockwise P–T paths that include nearly isothermal decompression processes, which suggest that they experienced subduction and subsequent rapid tectonic exhumation. SIMS and LA-ICP-MS U–Pb dating of zircons and 40Ar/39Ar dating of hornblende suggest that the metamorphism occurred at ∼430–390 Ma. Field occurrences, different protolith ages of the mafic granulites and amphibolites, and the considerable gap in peak P – T conditions between the amphibolite and mafic granulite boudinages and their country rock may suggest a mélange accumulation process during the Paleozoic caused by the Silurian–Devonian orogeny, which is possibly associated with the closure of the Liuyuan ocean, a branch of the Paleo-Asian ocean near the southern Central Asian Orogenic Belt. [ABSTRACT FROM AUTHOR]

Understanding the thermal behaviour of iron-containing amphiboles (AB2C5T8O22W2, C5 = M(1)2 M(2)2 M(3)) at atomic-level scale may have important implications in several fields, including metamorphic petrology, geophysics, and environmental sciences. Here, the thermally induced oxidation and decomposition of actinolite are studied by in situ high-temperature Raman spectroscopy and complementary thermogravimetric/mass-spectrometry analyses as well as X-ray diffraction of the products of amphibole decomposition. The effect of CFe2+ on dehydrogenation/dehydroxylation is followed by comparing the results on actinolite with those for tremolite. We show that mobile charge carriers, namely polarons (conduction electrons coupled to FeO6 phonons) and H+ cations, exist in actinolite at elevated temperatures ~ 1150–1250 K. The temperature-induced actinolite breakdown is a multistep process, involving (i) delocalization of e− from CFe2+ as well as of H+ from hydroxyl groups shared by Fe-containing M(1)M(1)M(3) species, which, however, remain in the crystal bulk; (ii) dehydrogenation and ejection of e− between 1250 and 1350 K, where actinolite can be considered as “oxo-actinolite”, as H+ also from hydroxyl groups next to M(1,3)(MgMgMg) configurations become delocalized and mostly remain in the crystal bulk; (iii) complete dehydroxylation and consequent structure collapse above 1350 K, forming an Fe3+-bearing defect-rich augitic pyroxene. The dehydrogenation of tremolite occurs at 1400 K, triggering immediately a disintegration of the silicate double-chain into single SiO4-chains and followed by a rearrangement of the amphibole octahedral strips and BCa2+ cations into pyroxene-type octahedral sheets at 1450 K. The result of tremolite decomposition is also a single-phase defect-rich clinopyroxene with an intermediate composition on the diopside–clinoenstatite join. [ABSTRACT FROM AUTHOR]

Ferro-ferri-homblende is a new member of the amphibole supergroup (IMA-CNMNC 2015-054). It has been found in a rock specimen from the historical collection of Leandro De Magistris, which was collected at the Traversella mine (Val Chiusella, Ivrea, Piemonte, Italy). The specimen was catalogued as 'speziaite', and contains a wide range of amphibole compositions from tremolite/actinolite to magnesio-hastingsite. The end-member formula of ferro-ferri-homblende is A□BCa2 C(Fe2+4Fe3+)T(Si7Al) O22W(OH)2 , which requires SiO2 43.41, Al2O3 5.26, FeO 29.66, Fe2O3 8.24 CaO 11.57, H2O 1.86, total 100.00 wt.%. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement for the holotype crystal is A(Na0.10K0.13)∑=0.23B(Ca1.93Na0.07)∑=2.00C(Mg1.16Fe2+3.21Mn0.06Fe3+0.45Al0.12Ti0.01)∑=5.01T(Si7.26Al0.74)∑=8.00 O22W(OH1.89F0.01Cl0.10)∑=2.00. Ferro-ferri-homblende is biaxial (-), with α = 1.697(2), β = 1.722(5), γ = 1.726(5) and 2V (meas.) = 35.7(1.4)°, 2V (calc.) = 43.1°. The unit-cell parameters are a = 9.9307(5), b = 18.2232(10), c = 5.3190(3) Å, β = 104.857(1)°, V = 930.40 (9) Å3, Z= 2, space group C2/m. The a:b:c ratio is 0.545:1:0.292. The strongest eight reflections in the powder X-ray pattern [d values (in Å), I, (hkl)] are: 8.493, 100, (110); 2.728, 69, (151); 3.151,47, (310); 2.555, 37, (2̅02); 2.615, 32, (061); 2.359, 28, (3̅51); 3.406, 26, (131); 2.180, 25, (261). Type material is deposited in the collections of the Museo di Mineralogia, Dipartimento di Scienze della Terra e dell' Ambiente, Università di Pavia, under the catalogue number 2015-01. Sample M/U15285 from the historical collection of Luigi Colomba, presently at the Museo Regionale di Scienze Naturali di Torino, was also checked, and the presence of ferro-ferri-homblende was confirmed. [ABSTRACT FROM AUTHOR]

Metaultramafic rocks (MUR) in the Ashe Metamorphic Suite (AMS) of northwestern North Carolina include quartz ± feldspar-bearing QF-amphibolites and quartz-deficient, locally talc-, chlorite-, and/or Mg-amphibole-bearing TC-amphibolites. Some workers divide TC-amphibolites into Todd and Edmonds types, based on mineral and geochemical differences, and we provisionally add a third type – olivine ± pyroxene-rich, Rich Mountain-type rocks. Regionally, MUR bodies range from equant, Rich Mountain- to highly elongate, Todd-TC-amphibolite-type bodies. The MURs exhibit three to five mineral associations containing assemblages with olivine, anthophyllitic amphibole, Mg-hornblende, Mg-actinolite, cummingtonite, and serpentine representing decreasing eclogite to greenschist facies grades of metamorphism over time. MUR protoliths are difficult to determine. Southwestern MUR bodies have remnant olivine ± pyroxene-rich assemblages representing ultrabasic-basic, dunite-peridotite-pyroxenite protoliths. Northeastern TC-amphibolite MURs contain hornblende and actinolitic amphiboles plus chlorites – aluminous and calcic assemblages suggesting to some that metasomatism of basic, QF-amphibolites yields all TC-amphibolites. Yet MgO-CaO-Al2O3and trace element chemistries of many TC-amphibolites resemble compositions of plagioclase peridotites. We show that a few AMS TC-amphibolites had basaltic/gabbroic protoliths, while presenting arguments opposing application of the metasomatic hypothesis toallTC-amphibolites. We establish that MUR bodies are petrologically heterolithic and that TC-amphibolites are in contact with many rock types; that those with high Cr, Ni, and Mg have olivine- or pyroxene-dominated protoliths; that most exhibit three or more metamorphic mineral associations; and that contacts thought to be metasomatic are structural. Clearly, different MUR bodies have different chemistries representing various protoliths, and have different mineral assemblages, reflecting both chemical composition and metamorphic history. Spot sampling of heterolithic MUR bodies does not reveal MUR body character or history or allow ‘type’ designations. We recommend that the subdivision of MUR bodies into ‘types’ be abandoned and that the metasomatic hypothesis be carefully applied. AMS MURs and associated metamafic rocks likely represent fragments of dismembered ophiolites from various ophiolite types. [ABSTRACT FROM PUBLISHER]

Microanalysis of Fe3+/ΣFe in geological samples using synchrotron-based X-ray absorption spectroscopy has become routine since the introduction of standards and model compounds. Existing calibrations commonly use least-squares linear combinations of pre-edge data from standard reference spectra with known coordination number and valence state acquired on powdered samples to avoid preferred orientation. However, application of these methods to single mineral grains is appropriate only for isometric minerals and limits their application to analysis of in situ grains in thin sections. In this work, a calibration suite developed by acquiring X-ray absorption near-edge spectroscopy (XANES) data from amphibole single crystals with the beam polarized along the major optical directions (X, Y, and Z) is employed. Seven different methods for predicting %Fe3+ were employed based on (1) areanormalized pre-edge peak centroid, (2) the energy of the main absorption edge at the location where the normalized edge intensity has the highest R2 correlation with Fe3+/ΣFe, (3) the ratio of spectral intensities at two energies determined by highest R2 correlation with Fe3+/ΣFe, (4) use of the slope (first derivative) at every channel to select the best predictor channel, (5 and 6) partial least-squares models with variable and constant numbers of components, and (7) least absolute shrinkage and selection operator models. The latter three sophisticated multivariate analysis techniques for predicting Fe3+/ΣFe show significant improvements in accuracy over the former four types of univariate models. Fe3+/ΣFe can be measured in randomly oriented amphibole single crystals with an accuracy of ±5.5-6.2% absolute. Multivariate approaches demonstrate that for amphiboles main edge and EXAFS regions contain important features for predicting valence state. This suggests that in this mineral group, local structural changes accommodating site occupancy by Fe3+ vs. Fe2+ have a pronounced (and diagnostic) effect on the XAS spectra that can be reliably used to precisely constrain Fe3+/ΣFe. [ABSTRACT FROM AUTHOR]

Actinolite dissolution rates in aqueous HCl and aqueous CaCl 2 –HCl have been measured at temperatures ranging from 25 to 400 °C at 23 MPa, under conditions far from equilibrium, using a flow-through reactor. The relative release rates for the various elements in actinolite due to breaking of metal–oxygen bonds are all different. All of the release rates vary with temperature and pH. The release rate of Si increases as temperature rises from 20 to 300 °C, but then decreases at higher temperatures. Other metallic ions, such as Ca, Mg, Fe, and Al, are all released more rapidly than Si at temperatures between 25 and 300 °C, but more slowly at temperatures ⩾300 °C. The ratios of m Ca / m Si and m Mg / m Si in the effluent at 200 °C are close to the stoichiometric proportions of these elements in actinolite, but differ from stoichiometric values at temperatures both above and below 200 °C. Actinolite dissolution in aqueous HCl at 100 °C yields element ratios close to stoichiometric values in the mineral, but again the ratios vary at higher and lower temperatures. Our experiments demonstrate that, under conditions far from equilibrium, dissolution rates depend on both pH and the activity of aqueous Mi Zi + , where Z i is the valence of the metal Mi in the mineral and Mi Zi + refers to Ca 2+ , Mg 2+ , or Al 3+ . The ion-exchange model suggests that metal–hydrogen ion exchange reaction on the surface is a key step for mineral dissolution, and that a Si-rich, M i -deficient precursor complex is formed on the mineral surface at temperatures <300 °C. Using our experimental data, we express the release rate of Si ( r ) as follows: - r + = A exp ( - E A / RT ) ( ( a H + ) Zi / a Mi Zi + ) α where α is the order with respect to the ratio of activity of hydrogen ions and dissolved metal ions M i . The Mg–H exchange coefficient, α , is 0.55 at 100 °C. The apparent activation energy E A = 14.4 kJ/mol, and A = 0.23 × 10 −3 m cm −2 s −1 . Our results show that water properties vary strongly within the critical region, which affects the dissolution mechanism. Thus, the release rates for various elements at temperatures above 300 °C are different from those at temperatures below 300 °C. High resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) studies indicate that a Fe(Al)-rich, Si-deficient layer is formed on the surface at temperatures above 300 °C. X-ray photoelectron spectroscopy (XPS) analyses show that the surface layer that formed by reaction with aqueous HCl at 400 °C is a hydrated silicate, composed of Si–OH and M i –OH, as well as Si–O and M i –O bonds. [ABSTRACT FROM AUTHOR]

Anisotropy of magnetic susceptibility (AMS) is often used as a proxy for mineral fabric in deformed rocks. To do so quantitatively, it is necessary to quantify the intrinsic magnetic anisotropy of single crystals of rock-forming minerals. Amphiboles are common in mafic igneous and metamorphic rocks and often define rock texture due to their general prismatic crystal habits. Amphiboles may dominate the magnetic anisotropy in intermediate to felsic igneous rocks and in some metamorphic rock types, because they have a high Fe concentration and they can develop a strong crystallographic preferred orientation. In this study, the AMS is characterized in 28 single crystals and 1 crystal aggregate of compositionally diverse clino- and ortho-amphiboles. High-field methods were used to isolate the paramagnetic component of the anisotropy, which is unaffected by ferromagnetic inclusions that often occur in amphibole crystals. Laue imaging, laser ablation-inductively coupled plasma-mass spectrometry, and Mössbauer spectroscopy were performed to relate the magnetic anisotropy to crystal structure and Fe concentration. The minimum susceptibility is parallel to the crystallographic a*-axis and the maximum susceptibility is generally parallel to the crystallographic b-axis in tremolite, actinolite, and hornblende. Gedrite has its minimum susceptibility along the a-axis, and maximum susceptibility aligned with c. In richterite, however, the intermediate susceptibility is parallel to the b-axis and the minimum and maximum susceptibility directions are distributed in the a-c plane. The degree of anisotropy, kʹ, increases generally with Fe concentration, following a linear trend: kʹ = 1.61 × 10-9 Fe - 1.17 × 10-9 m3/kg. Additionally, it may depend on the Fe2+/Fe3+ ratio. For most samples, the degree of anisotropy increases by a factor of approximately 8 upon cooling from room temperature to 77 K. Ferroactinolite, one pargasite crystal and riebeckite show a larger increase, which is related to the onset of local ferromagnetic (s.l.) interactions below about 100 K. This comprehensive data set increases our understanding of the magnetic structure of amphiboles, and it is central to interpreting magnetic fabrics of rocks whose AMS is controlled by amphibole minerals. [ABSTRACT FROM AUTHOR]

Metamorphic rocks experience change in the mode of deformation from ductile flow to brittle failure during their exhumation. We investigated the spatial variation of phengite K- Ar ages of pelitic schist of the Sambagawa metamorphic rocks (sensu lato) from the Saruta River area, central Shikoku, to evaluate if those ages are disturbed by faults or not. As a result, we found that these ages change by ca 5 my across the two boundaries between the lower-garnet and albite-biotite, and the albite-biotite and upper-garnet zones. These spatial changes in phengite K- Ar ages were perhaps caused by truncation of the metamorphic layers by large-scale normal faulting at D2 phase under the brittle-ductile transition conditions ( ca 300°C) during exhumation, because an actinolite rock was formed along a fault near the former boundary. Assuming that the horizontal metamorphic layers and a previously estimated exhumation rate of 1 km/my before the D2 phase, the change of 5 my in phengite K- Ar ages is converted to a displacement of about 10 km along the north-dipping, low-angle normal fault documented in the previous study. Phengite 40 Ar-39 Ar ages ( ca 85 to 78 Ma) in the actinolite rock could be reasonably comparable to the phengite K- Ar ages of the surrounding non-faulted pelitic schist, because the K- Ar ages of pelitic schist could have been also reset at temperatures close to the brittle-ductile transition conditions far below the closure temperature for thermal retention of argon in phengite (about 500-600°C). [ABSTRACT FROM AUTHOR]

The latest Cretaceous to early Palaeogene Orocopia Schist and related units are generally considered a low-angle subduction complex that underlies much of southern California and Arizona. A recently discovered exposure of Orocopia Schist at Cemetery Ridge west of Phoenix, Arizona, lies exceptionally far inland from the continental margin. Unexpectedly, this body of Orocopia Schist contains numerous blocks, as large as ~300 m, of variably serpentinized mantle peridotite. These are unique; elsewhere in the Orocopia and related schists, peridotite is rare and completely serpentinized. Peridotite and metaperidotite at Cemetery Ridge are of three principal types: (1) serpentinite and tremolite serpentinite, derived from dunite; (2) partially serpentinized harzburgite and olivine orthopyroxenite (collectively, harzburgite); and (3) granoblastic or schistose metasomatic rocks, derived from serpentinite, made largely of actinolite, calcic plagioclase, hercynite, and chlorite. In the serpentinite, paucity of relict olivine, relatively abundant magnetite (5%), and elevated Fe3+/Fe indicate advanced serpentinization. Harzburgite contains abundant orthopyroxene, only slightly serpentinized, and minor to moderate (1–15%) relict olivine. Mantle tectonite fabric is locally preserved. Several petrographic and geochemical characteristics of the peridotite at Cemetery Ridge are ambiguously similar to either abyssal or mantle-wedge (suprasubduction) peridotites and serpentinites. Least ambiguous are orthopyroxene compositions. Orthopyroxene is distinctively depleted in Al2O3, Cr2O3, and CaO, indicating mantle-wedge affinities. Initial interpretation of field and petrologic data suggests that the peridotite blocks in the Orocopia Schist subduction complex at Cemetery Ridge may be derived from the leading corner or edge of a mantle wedge, presumably in (pre-San Andreas fault) southwest California. However, derivation from a subducting plate is not precluded. [ABSTRACT FROM AUTHOR]

The dissolution rates of the minerals actinolite and chlorite were determined from metabasalt element release rates measured at 25 °C and 2 < pH < 12 in mixed flow reactors. At pH 2.0 and 3.2, chlorite rates are 3 and 5 times faster, respectively, than corresponding actinolite rates, whereas the Si release rates from metabasalt are intermediate between chlorite and actinolite rates. In contrast, at pH 7.2 and 12.0, chlorite, actinolite and the metabasalt release Si at the same rates within analytical uncertainties. At pH 6.3, it was only possible to obtain the chlorite dissolution rate; at this pH the measured chlorite dissolution rate is 10 − 11.86 mol/m 2 /s. Mineral dissolution rates obtained in this study are within the range of corresponding values reported in the literature. This observation suggests that the dissolution rates of major-constituent minerals in a multi-phase rock are not affected by the presence of the other minerals. This conclusion validates the common assumption that the dissolution rate of an individual mineral is equal to that of the same mineral in a dissolving multi-mineralogic rock, at least for major constituents. [ABSTRACT FROM AUTHOR]

Serpentine, and other asbestos minerals, are considered potential hazards to human respiratory health. It has been postulated that the surface characteristics of these substances, such as surface charge and adsorbed metals, notably Fe and other transition metals, may be the major agents responsible for their toxicity. There is a general consensus that the amphibole group of minerals possesses a greater health risk than serpentines dominated by chrysotile. There have been suggestions that natural processes can alter the surfaces of these minerals and reduce their potency. This study examined the effects of carbonic acid, oxalic acid and hydrochloric acid on the surface characteristics of two trioctahedral minerals, actinolite (amphibole) and chrysotile (serpentine), and compared the results to a non-asbestiform, dioctahedral mineral, kaolinite. Results confirm that the treatments alter the mineral surfaces by changing the zeta potential of the asbestiform minerals from positive to negative and by removing considerable amounts on non-crystalline Fe and other metals. X-ray analyses indicated that mineral structure was little affected by the treatments, and TOF-SIMS revealed that treatments did remove surface adsorbed metals and cations in octahedral coordination within the samples. [ABSTRACT FROM AUTHOR]

Muiraquitãs, lithic artifacts found in the Amazon basin, have been considered to be Asian in origin, or to have been sculpted by the legendary female Amazon warriors. These pieces are now very rare, and are found mainly in museum collections. In the present study, the mineralogical and chemical content of 23 specimens from the collections of the Museu de Gemas (Gemstone Museum) and Museu do Encontro (Meeting Museum) in Belém, Brazil, were analyzed. Most of the pieces were made of minerals commonly found in Brazil - quartz, albite, microcline, variscite, anorthite, and tremolite (the equivalent of nephritic jade). However, four of the pieces were made of jadeite, that is, jadeitic jade, which is unknown in the Amazon basin or in other parts of Brazil. The confirmation of the presence of this mineral in some of the artifacts reopens the debate on the mineralogical origin of the muiraquitãs found in the Amazon basin. Before the present discovery, their origin was defended as Amazonian due to the absence of jadeite jade in the searched pieces and the fact that jadeite was not found in Brazil but in Central America and Asia. [ABSTRACT FROM AUTHOR]

When asbestos fibres become airborne, they can be inhaled into the lungs, where they may cause significant health problems. The latter includes progressive pulmonary fibrosis (asbestosis), pleural disease (effusion and pleural plaques) and malignancies such as bronchogenic carcinoma and malignant mesothelioma. The term asbestos applies to a group of hydrated fibrous mineral silicates including those belonging to the serpentine group of phyllosilicates (chrysotile) and amphiboles. However, only the 'asbestiform varieties' of amphiboles such as grunerite (amosite), riebeckite (crocidolite), anthophyllite, tremolite and actinolite are regarded as asbestos (s.s.). This implies that 'non-asbestiform varieties' of such minerals, that nevertheless generate acicular cleavage fragments, cannot be regarded as asbestos s.s. We argue that a discussion on the term asbestos goes beyond mere semantics, because for environmental regulatory bodies, the definition of a term can make the difference between classifying a mineral as harmful or non-harmful. A case of mesothelioma in the small mining town of La Higuera, northern Chile, may shed some light into this matter, because this form of cancer is almost always caused by exposure to asbestos. The town hosts about 20,000 t of fine-grained tailings left behind after flotation of Cu sulphides during 1950-1979. The ore was extracted from actinolite-rich, copper-iron vein deposits. We show that, if a 'non-asbestiform variety' of amphibole (e.g. La Higuera actinolite) is finely ground, it will cleave to asbestos-like acicular crystals and as such has the potential to induce similar health hazards to those posed by asbestos (s.s.). [ABSTRACT FROM AUTHOR]

The ∼750 km2 Dayman dome of the Late Cretaceous Suckling-Dayman massif, eastern Papua New Guinea, is a domed landform that rises to an elevation of 2850 m. The northern edge of the dome is a fault scarp >1000 m high that is now part of an active microplate boundary separating continental crust of the New Guinea highlands from continental and oceanic crust of the Woodlark microplate. Previous work has shown that a parallel belt of eclogite-bearing core complexes north-east of the Dayman dome were exhumed from up to 24–28 kbar in the last few millions of years. The remarkably fresh and lightly eroded scarp of the Dayman dome exposes shallowly-dipping mylonitic (S1) metabasite rocks (500 m thick) on the northern flank of Mount Dayman. Field relationships near the base of this scarp show a cross cutting suite of ductile and brittle meso-structures that includes: (i) rare ductile S2 folia with a shallowly ESE-plunging mineral elongation lineation defined by sodic-calcic blue amphibole; (ii) narrow steeply-dipping ductile D2 shear zones; and (iii) semi-brittle to brittle fault zones. Pumpellyite-actinolite facies assemblages reported by previous workers to contain local aragonite, lawsonite and/or glaucophane are found in the core of the complex at elevations greater than 2000 m. These assemblages indicate peak metamorphic pressures of 6–9.5 kbar, demonstrating exhumation of the core of the Dayman dome from depths of 20–30 km. The S1 metamorphic mineral assemblage in metabasite includes actinolite-chlorite-epidote-albite-quartz-calcite-titanite, indicative of greenschist facies conditions for the main deformation. New mineral equilibria modelling suggests that this S1 assemblage evolved at 5.9–7.2 kbar at ∼425 °C. Modelling variable Fe3+ indicates that the sodic-calcic blue amphibole (D2) formed under a higher oxidation state compared with the S1 assemblage, probably at <4.5 kbar. A SE-dipping, Mio-Pliocene sedimentary sequence (Gwoira Conglomerate) forms a hangingwall block juxtaposed by low-angle fault contact with the metabasite footwall. Prehnite-bearing D3 brittle fault zones separate the two blocks and likely accommodated the final exhumation of the S1 greenschist facies assemblage in the footwall. These results indicate that the extensive Mt Dayman fault surface coincides with a domed S1 greenschist facies foliation that was last active at >20 km depth. Exhumation of this foliation must therefore be controlled by brittle faults of the active microplate boundary that are largely not observed in the study area. The structural record of the final exhumation of the Dayman dome to the surface was likely lost as a result of erosion, poor exposure or wide spacing of semi-brittle to brittle fault zones. [ABSTRACT FROM AUTHOR]

During a repair and reconstruction project of an unpaved highway in a remote region of Alaska, workers discovered, after construction had commenced, that the materials used from a local material site contained asbestos (variously described as tremolite or actinolite). The regional geology indicated the presence of ultramafic rock, which often contains asbestos. Evaluation of asbestos exposure to workers, their equipment, and living quarters was required, as was the possible future exposure of workers and the general public to asbestos already used in the roadway construction. In addition, a decision was needed on whether to use materials from the contaminated site in the future. Of the almost 700 breathing zone air monitoring samples taken of the workers, 3% of the samples indicated exposures at or near 0.1 f/cc by the National Institute for Occupational Safety and Health (NIOSH) 7400 phase contrast microscopy (PCM) procedure. Thirty-six of the PCM samples underwent transmission electron microscopy (TEM) analysis by the NIOSH 7402 procedure, which indicated that about 40% of the fibers were asbestos. After classifying samples by tasks performed by workers, analysis indicated that workers, such as road grader operators who ground or spread materials, had the highest exposures. Also, monitoring results indicated motorist exposure to be much less than 0.1 f/cc. The design phase of any proposed construction project in regions that contain ultramafic rock must consider the possibility of amphibole contamination of roadway materials, and budget for exploration and asbestos analysis of likely materials sites. [ABSTRACT FROM AUTHOR]

Abstract: A metamorphic inversion along the Asemigawa section of the Besshi unit in the Sambagawa high P/T metamorphic zone has been explained previously by S-vergent major recumbent folding or thrusting. Through careful structural field investigations, however, we recognize the D2 Asemigawa detachment fault at the boundary of the highest-grade (oligoclase–biotite zone) thermal culmination in the belt. We have also discovered a series of normal faults in the hanging wall of the major detachment in the upper domain and a series of thrust faults bounding every metamorphic mineral zone of the footwall in the lower domain. Outcrop-scale D2 asymmetric folds are closely associated with axial-planar pressure-solution cleavages, and are genetically related to the above D2 normal faulting and thrusting as fault-propagation folds. Northward fold vergence is found only in the upper domain and southward vergence is found only in the lower domain. Exceptions to this rule occur only for parasitic folds in the overturned limbs of mesoscopic folds, which indicates flexural slip as a likely fold mechanism. We propose an extrusion wedge model for the inverted metamorphism and accordingly, this mechanism may also account for a large part of the exhumation of the Sambagawa metamorphic rocks, although westward shear at the time of D1 stretching lineation has partly contributed to the exhumation by counter-flow in the accretionary wedge. We infer that M1 with its retrograde actinolite schists represents a D1 ductile shear zone, but it contributes as much as a component of the D2 Asemigawa detachment, other normal and thrust faults, and asymmetric folds, as reactivated brittle shear zones. Thus, shear direction had changed orthogonally and drastically between ductile D1 stretching and ductile–brittle transition to brittle D2 extrusion. We infer that this transition reflects the collision of an actively spreading mid-ocean ridge and is a consequence of increased coupling of plates and orogen-normal stress, followed by oblique subduction. D0 and D−1 record eastward down-flow during the oblique underthrusting of oceanic plate, before peak metamorphism M1. [Copyright &y& Elsevier]

A calibration is presented for an activity–composition model for amphiboles in the system Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O (NCFMASHO), formulated in terms of an independent set of six end-members: tremolite, tschermakite, pargasite, glaucophane, ferroactinolite and ferritschermakite. The model uses mixing-on-sites for the ideal-mixing activities, and for the activity coefficients, a macroscopic multicomponent van Laar model. This formulation involves 15 pairwise interaction energies and six asymmetry parameters. Calibration of the model is based on the geometrical constraints imposed by the size and shape of amphibole solvi inherent in a data set of 71 coexisting amphibole pairs from rocks, formed over 400–600 °C and 2–18 kbar. The model parameters are calibrated by combining these geometric constraints with qualitative consideration of parameter relationships, given that the data are insufficient to allow all the model parameters to be determined from a regression of the data. Use of coexisting amphiboles means that amphibole activity–composition relationships are calibrated independently of the thermodynamic properties of the end-members. For practical applications, in geothermobarometry and the calculation of phase diagrams, the amphibole activity–composition relationships are placed in the context of the stability of other minerals by evaluating the properties of the end-members in the independent set that are in internally consistent data sets. This has been performed using an extended natural data set for hornblende–garnet–plagioclase–quartz, giving the small adjustments necessary to the enthalpies of formation of tschermakite, pargasite and glaucophane for working with the Holland and Powell data set. [ABSTRACT FROM AUTHOR]

The magmatic and sub-solidus evolution of calcic amphiboles and Fe–Ti oxides was investigated in the Neoproterozoic Frog Lake pluton, Nova Scotia, Canada, in order to understand the relationship between the history of hydrous magma and the resulting mineralogy. The pluton occurs as sheet-like bodies of hornblende gabbro and hornblendite, with lesser tonalite dykes and granite bodies, interlayed with screens of medium-grade metamorphic country rock. Small, diffuse clots of felsic minerals are present in the gabbro. The subsolidus growth of actinolite occurs in early clinopyroxenes and amphiboles. Ilmenite is the dominant Fe–Ti oxide, as interstitial magmatic crystals. The increase of Mn towards the margin of the ilmenite crystals indicates a gradual increase in oxygen fugacity with time, leading to the precipitation of titanite and ferrohypersthene. The replacement of titanite by ilmenite and ilmenite lamellae in the amphiboles suggests subsequent reducing conditions during the sub-solidus crystallisation. The gabbros in the coeval, but apparently shallower, Jeffers Brook granodiorite laccolith have dominant magnetite and Mg-rich subsolidus amphiboles, which are indicative of high oxygen fugacity. The differences between the two plutons suggest that there was a greater flux of hydrothermal water through the sheet-like architecture of the Frog Lake pluton. [ABSTRACT FROM AUTHOR]

Exhumed subduction zones frequently show widespread actinolite-chlorite (Act-Chl) dominated compositions, suggesting that this may play an important role in controlling megathrust fault slip. We investigate the frictional behavior of simulated Act-Chl (85:15) gouge mixtures derived from natural mafic metamorphic rocks, under hydrothermal conditions using a ring shear deformation apparatus. Experiments were performed at effective normal stresses (σ n eff ) of 50–200 MPa, pore fluid pressures (P f) of 50–200 MPa, at temperatures (T) of 23–600 °C. In each experiment we applied a shear displacement (x) of ~10 mm at a constant sliding velocity (v) of 10 μm/s, followed by v -stepping in the range 0.3–100 μm/s, and slide-hold-slide (SHS) tests with hold times (t) ranging from 3 s to 3000 s. We quantified the rate- and state-dependent friction parameter (a - b), and investigated the effect of t on fault healing (Δ μ pk). The results showed no effects of temperature on the coefficient of friction (μ ≈ 0.6–0.7), or on (a - b), with some experiments showing persistent, displacement-hardening or -weakening trends. Nonetheless, effects of v and of normal stress (σ n = σ n eff + P f) on (a - b) fall into three temperature regimes: (1) T = 23–100 °C, (2) T = 200–400 °C, and (3) T = 500–600 °C. In Regimes (1) and (3), (a - b) > 0 for all conditions tested, whereas in Regime (2), (a - b) ≤ 0, at σ n eff = P f = 50 MPa and v = 0.3–3 μm/s. We discuss on the origin of persistent displacement-hardening or -weakening trends observed, and assess the implications of our data for subduction zone seismogenesis. Extrapolation of (a - b)-data using multiple linear regression suggests that high pore pressure ratios (>0.9) are needed to promote seismogenesis in faults cutting actinolite-chlorite compositions. • Act:Chl (85:15) gouge has a friction coefficient of 0.5-0.8 at 22-600°C, at σ n eff = P f = 50-200 MPa, at v = 0.3-100 μm/s. • Velocity-weakening is observed at 300-400°C (mainly) velocity-strengthening outside these conditions. • Increasing the pore pressure ratio λ = P f / σ n promotes v-weakening behaviour [ABSTRACT FROM AUTHOR]

Amphiboles are an important family of rock forming minerals, whose identification is crucial in provenance studies as well as in many other fields of geology, archaeology and environmental sciences. This study is aimed to find a quick way to characterize Ca-amphiboles in the tremolite (Ca2Mg5Si8O22(OH)2)–ferro–actinolite (Ca2Fe5Si8O22(OH)2) series. Raman spectroscopy is established as technique to perform non-destructive and quick analysis, with micrometric resolution, able to give the composition in terms of Mg/(Mg + Fe2+) ratio. To exploit the method, a preliminary characterization is performed by Scanning Electron Microscopy coupled with Energy-dispersed X-ray Spectroscopy (SEM-EDS). Two independent methods to evaluate the composition from the Raman data (aiming to an accuracy of about 5%), using the low-wavenumbers part of the spectrum and the OH stretching bands, are developed. The application of the proposed method to micro-Raman mappings and the possible use of handheld Raman spectroscopy to have compositional information on Ca-amphiboles are discussed. [ABSTRACT FROM AUTHOR]

The color of quartz and other minerals can be either caused by defects in the crystal structure or by finely dispersed inclusions of other minerals within the crystals. In order to investigate the mineral chemistry and genesis of the famous prase (green quartz) and amethyst association from Serifos Island, Greece, we used electron microprobe analyses and oxygen isotope measurements of quartz. We show that the color of these green quartz crystals is caused by small and acicular amphibole inclusions. Our data also shows that there are two generations of amphibole inclusions within the green quartz crystals, which indicate that the fluid, from which both amphiboles and quartz have crystallized, must have had a change in its chemical composition during the crystallization process. The electron microprobe data also suggests that traces of iron may be responsible for the amethyst coloration. Both quartz varieties are characterized by isotopic compositions that suggest mixing of magmatic and meteoric/marine fluids. The contribution of meteoric fluid is more significant in the final stages and reflects amethyst precipitation under more oxidizing conditions. [ABSTRACT FROM AUTHOR]

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]