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1.
Low‐T calorimetry is an experimental science that measures the thermodynamic function heat capacity, Cp(T), from which the standard third‐law entropy (298.15 K), S°, is calculated. The recent technological development of relaxation calorimetry allows both new experimental strategies and types of Cp investigations to be made, which were previously not possible. The Cp measurements are fast and automated and can be made on mg‐sized mineralogical samples between 2 and 400 K. These advantages, when careful measurement procedures are used, permit better determinations of Cp(T) behaviour. The Cp of synthetic single‐crystal MgO was measured between 5 and 302 K, and S° calculated using relaxation calorimetry to further investigate the method's precision and accuracy. A number of synthetic and natural end‐member or nearly end‐member compositions of silicate garnet were investigated in the past via adiabatic calorimetry, an old and established technique, and more recently and extensively with the relaxation method. First Cp(T) and S° results, using relaxation calorimetry, have been obtained on spessartine (Mn3Al2Si3O12) and knorringite (Mg3Cr2Si3O12). Furthermore, reinvestigations on pyrope (Mg3Al2Si3O12), almandine (Fe3Al2Si3O12), grossular (Ca3Al2Si3O12) and andradite (Ca3Al2Si3O12), often on multiple samples, have resolved uncertainties and certain problems with published thermodynamic data. S° can be affected by various low‐T physical phenomena, such as cooperative magnetic phase transitions or Schottky anomalies at temperatures of <15 K, which were not described fully in some older adiabatic calorimetric studies. New Cp results show that small differences in the thermodynamic behaviour between some natural and synthetic silicates may exist as demonstrated by extensive work on grossular. Important and “new” research questions on the thermodynamic behaviour of minerals are coming to light and are being investigated. The Cp behaviour and S° values for six silicate garnet end‐members are analysed and the latter are compared to the “best fit or optimized” S° values given in various internally consistent thermodynamic databases. Conclusions are drawn on what types and directions of calorimetric study are required in order to obtain better thermodynamic property determinations of minerals, as well as achieving a better understanding of the underlying microscopic physical behaviour that determines the macroscopic Cp and S° functions.  相似文献   

2.
The heat capacities of the international reference clay mineral chlorite CCa-2 from Flagstaff Hill, California, were measured by low temperature adiabatic calorimetry and differential scanning calorimetry, from 5 to 520 K (at 1 bar). The studied chlorite is a Fe-bearing trioctahedral chlorite with an intermediary composition between ideal clinochlore (Si3Al)(Mg5Al)O10(OH)8 and chamosite (Si3Al)(Fe5Al)O10(OH)8. Only few TiO2 impurities were detected in the natural chlorite sample CCa-2. Its structural formula, obtained after subtracting the remaining TiO2 impurities, is (Si2.633Al1.367)(Al1.116Mg2.952Mn0.012Ca0.011)O10(OH)8. From the heat capacity results, the entropy, standard entropy of formation and heat content of the chlorite were deduced. At 298.15 K, the heat capacity of the chlorite is 547.02 (±0.27) J mol−1 K−1 and the molar entropy is 469.4 (±2.9) J mol−1 K−1. The standard molar entropy of formation of the clay mineral from the elements is −2169.4 (±4.0) J mol−1 K−1.  相似文献   

3.
Relative compressibilities of five silicate garnets were determined by single-crystal x-ray diffraction on crystals grouped in the same high-pressure mount. The specimens include a natural pyrope [(Mg2.84Fe0.10Ca0,06) Al2Si3O12], and four synthetic specimens with octahedrally-coordinated silicon: majorite [Mg3(MgSi)Si3O12], calcium-bearing majorite [(Ca0.49Mg2.51)(MgSi)Si3012], sodium majorite [(Na1.88Mgp0.12)(Mg0.06Si1.94)Si3O12], and an intermediate composition [(Na0.37Mg2.48)(Mg0.13Al1.07 Si080) Si3O12]. Small differences in the compressibilities of these crystals are revealed because they are subjected simultaneously to the same pressure. Bulk-moduli of the garnets range from 164.8 ± 2.3 GPa for calcium majorite to 191.5 ± 2.5 GPa for sodium majorite, assuming K′=4. Two factors, molar volume and octahedral cation valence, appear to control garnet compression.  相似文献   

4.
Calcium-free carbonate cancrinite with formula unit Na8.28[Al5.93Si6.07O24](CO3)0.93(OH)0.49·3.64H2O (CAN) has been synthesized under hydrothermal conditions. The product has been characterized by the methods of scanning electronic microscopy and energy dispersive X-ray analysis, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis with FTIR of evolved gases (TGA–FTIR), and X-ray powder diffraction. The heat capacity of CAN has been measured from 6 to 259 K via low-temperature adiabatic calorimetry. A linear combination of Einstein functions has been used to approximate the obtained data on the heat capacity. The thermal contributions to the entropy and enthalpy of CAN in the temperature range 0–300 K have been calculated from these data. The heat capacity and third-law absolute entropy of CAN at 298.15 K are 1,047 ± 30 and 1,057 ± 35 J mol?1 K?1, respectively. High-temperature oxide-melt solution calorimetry has been used to determine the enthalpy of formation from elements of CAN at 298.15 K; the value equals ?14,684 ± 50 kJ mol?1. The Gibbs energy of formation from elements at 298.15 K has been calculated and totaled ?13,690 ± 51 kJ mol?1.  相似文献   

5.
The thermochemical study of two natural trioctahedral Mg–Fe chlorites—clinochlores was carried out using high-temperature melt solution calorimetry with a Tian–Calvet microcalorimeter. The enthalpies of formation of clinochlores of compositions (Mg4.9Fe 0.3 2+ Al0.8)[Si3.2Al0.8O10](OH)8 (–8811 ± 12 kJ/mol) and (Mg4.3Fe 0.7 2+ Al1.0)[Si3.0Al1.0O10](OH)8 (–8696 ± 13 kJ/mol) from elements were determined. The values of the standard entropies and the Gibbs energies of formation of the studied natural minerals as well as thermodynamic properties of Mg–Fe chlorites of theoretical composition were estimated.  相似文献   

6.
The low-temperature heat capacity of knorringite garnet (Mg3Cr2Si3O12) was measured between 2 and 300 K, and thermochemical functions were derived from the results. The measured heat capacity curves show a sharp lambda-shaped anomaly peaking at around 5.1 K. Magnetic susceptibility data show that the transition is caused by antiferromagnetic ordering. From the C p data, we suggest a standard entropy (298.15 K) of 301 ± 2.5 J mol?1 K?1 for Mg3Cr2Si3O12. The new data are also used in conjunction with previous experimental results to constrain ?H f ° for knorringite.  相似文献   

7.
This study is devoted to the physicochemical and mineralogical characterizations of palygorskite from Marrakech High Atlas, Morocco. The raw clay and its Na+-saturated <2 μm fraction were characterized using chemical, structural, and thermal analytical techniques. Measurements of specific surface area and porous volume are reported. The clay fraction was found to be made up of 95 % of palygorskite and 5 % of sepiolite. An original feature of this palygorskite is its deficiency in zeolitic H2O. The half-cell structural formula of its dehydrated form was determined on the basis of 21 oxygens to be (Si7.92Al0.08)(Mg2.15Al1.4Fe0.4Ti0.05 $ \square_{1} $ )(Ca0.03Na0.08K0.04)O21, while the hydrated form could be formulated as (Si7.97Al0.03)(Mg2.17Al1.46Fe0.40Ti0.05)(Ca0.03Na0.07K0,03)O20.18(OH)1.94(OH2)3.88·2.43 H2O. These formulas show that the (Al3++Fe3+)/Mg2+ ratio is around 0.84, revealing a pronounced dioctahedral character. Further, inside its octahedral sheet, it was determined that the inner M1 sites are occupied by vacancies, whereas the M2 sites are shared between 90 % of trivalent cations (78 % for Al3+ and 22 % for Fe3+), 7.5 % of Mg2+, and 2.5 % of Ti4+, all of them linked to 1.94 of structural hydroxyls. The two remaining Mg2+ by half-cell occupy edge M3 sites and are coordinated to 3.88 molecules of OH2. Channels of this palygorskite are deficient in zeolitic H2O since they contain only 2.43 H2O molecules. A correlation was found between these results and the observation of very intense and well-resolved FTIR bands arising from dioctahedral domains (mainly Al2OH, Fe2OH, and AlFeOH) along with very small responses from a trioctahedral domain (Mg3OH). Accordingly, a schematic representation of the composition of the octahedral sheet was proposed. The cation exchange capacity, specific surface area, and total pore volume were also assessed to be ca. 21.2 meq/100 g, 116 m2/g, and 0.458 cm3/g, respectively.  相似文献   

8.

Polarized absorption spectra of natural piemontite (Ca1.802Mn 2+0.178 Mg0.025) (Mn 3+0.829 Fe 3+0.346 Al1.825) [(Si2.992Al0.008) O12OH], viridine (Al1.945Mn 3+0.033 Fe 3+0.063 Mg0.003) [O|Si0.970 O4], and kanonaite (Al1.291Mn 3+0.682 Fe 3+0.019 ) [O|Si1.006 O4] were measured at 295 and ca. 100 K. For piemontite, lowering the temperature resulted in a sharpening of broad bands in the 10 000–25 000 cm−1 region supporting their assignment to single ion Mn3+ in M3 non-centrosymmetric sites.

Alternatively, in kanonaite, temperature behaviour pointed to a slightly stronger influence of vibronic coupling on strong bands near 16 000 and 22 000 cm−1, which supported an interpretation of Mn3+ in nearly centrosymmetric M1 sites. Measurements at ca. 100 K show pronounced fine structure in the viridine spectra which is attributed to Fe3+. The ɛ values for Mn3+ spin-allowed bands in the three minerals lie in the range 18 to 227 [1·g-atom−1·cm−1].

For the same band and polarisation, ɛ values in Mn3+-bearing andalusite-type minerals viridine and kanonaite are the same, which indicates an absence of strong magnetic coupling effects between Mn3+ ions in the andalusite type structure down to ca. 100 K.

In silicates, the high ɛ values for Mn3+ spin-allowed bands, in comparison to those obtained for Fe2+ spin-allowed bands from sites of “similar distortion”, is attributed to a higher degree of covalency in the Mn3+-O bonds compared to the Fe2+-O bonds, as a result of the higher valence state of manganese.

  相似文献   

9.
Equations for the configurational entropy and homogeneous equilibria in Ca2MgSi2O7-Ca2SiAl2O7 melilites are derived for a site constraint that does not permit Mg on the smaller T2 tetrahedral sites. This constraint leads to one ordering parameter and one composition parameter. The maximum configurational entropy for perfectly ordered crystalline solutions is 3.795 cal K–1 mol–1, corresponding to the structural formula Ca2(Mg0.33Al0.67) (Si0.67Al0.33)2O7 and not the equimolar composition Ca2(Mg0.5Al0.5)(Si0.75Al0.25)2O7. Similarly, the configuration Ca2(Si0.33Al0.67)(Si0.33Al0.67)2O7 has the maximum entropy for the gehlenite end-member composition. The tabulated entropy of end-member gehlenite at 298.15 K must be corrected by at least 2Rln2, which corresponds to a substantial correction to its Gibbs energy at high temperature. The same corrections are applicable to other minerals having two crystallographically distinct sites in a 21 ratio and where the same configurational entropy equation applies: MgFe2O4 (magnesioferrite), NiFe2O4 (trevorite), TiFe2O4 (ulvospinel), TiMg2O4, TiZn2O4, CuFe2O4, and TiFe2O5 (pseudobrookite) inasmuch as these substances prefer the same inverse ordered state as gehlenite at low temperatures. The effects of the ideal enthalpy and entropy on temperatures of homogeneous equilibria in gehlenite and MgTi2O5 are evaluated. Geological-thermometer phase diagrams of the long-range ordering parameter plotted against temperature have a sigmoidal shape for these minerals owing to the fact that this type of disordering is non-convergent.  相似文献   

10.
The paper presents the results of a thermochemical and thermal study of cancrinite, (Na6.93Ca0.545K0.01)Σ7.485[(Si6.47Al5.48Fe0.05)Σ12O24](CO3)1.25 · 2.30 H2O, and cancrisilite, (Na7.17 Ca0.01)Σ7.18[(Si7.26Al4.70Fe0.04)Σ12O24][(CO3)1.05(OH)0.21(PO4)0.04(SO4)0.01] · 2.635 H2O, from the Khibina-Lovozero Complex, Kola Peninsula, Russia. Stages of the thermal decomposition of these minerals were studied using IR spectroscopy. The enthalpies of formation of the minerals from elements were determined by melt drop solution calorimetry: Δ f H el 0 (298.15 K) = ?14 490 ± 16 kJ/mol for cancrinite and ?14302 ± 17 kJ/mol for cancrisilite. The values of Δ f H el 0 (298.15 K), S o(298.15 K), and Δ f H el 0 (298.15 K) are determined for cancrinite and cancrisilite of theoretical composition.  相似文献   

11.
Microprobe analysis, single crystal X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, and X-ray absorption spectroscopy were applied on Fe-rich osumilite from the volcanic massif of Mt. Arci, Sardinia, Italy. Osumilite belongs to the space group P6/mcc with unit cell parameters a = 10.1550(6), c = 14.306(1) Å and chemical formula (K0.729)C (Na0.029)B (Si10.498 Al1.502)T1 (Al2.706 Fe 0.294 2+ )T2 (Mg0.735 Mn0.091 Fe 1.184 2+ )AO30. Structure refinement converged at R = 0.0201. Unit cell parameter a is related to octahedral edge length as well as to Fe2+ content, unlike the c parameter which does not seem to be affected by chemical composition. The determination of the amount of each element on the mineral surface, obtained through X-ray photoelectron spectroscopy high-resolution spectra in the region of the Si2p, Al2p, Mg1s and Fe2p core levels, suggests that Fe presents Fe2+ oxidation state and octahedral coordination. Two peaks at 103.1 and 100.6 eV can be related to Si4+ and Si1+ components, respectively, both in tetrahedral coordination. The binding energy of Al2p, at 74.5 eV, indicates that Al is mostly present in the distorted T2 site, whereas the Mg peak at 1,305.2 eV suggests that this cation is located at the octahedral site. X-ray absorption at the Fe L2,3-edges confirms that iron is present in the mineral structure, prevalently in the divalent state and at the A octahedral site.  相似文献   

12.
The paper reports results of an experimental thermochemical study (in a heat-flux Tian-Calvet microcalorimeter) of montmorillonite from (I) the Taganskoe and (II) Askanskoe deposits and (III) from the caldera of Uzon volcano, Kamchatka. The enthalpy of formation Δ f H el 0 (298.15 K) of dehydrated hydroxyl-bearing montmorillonite was determined by melt solution calorimetry: ?5677.6 ± 7.6 kJ/mol for Na0.3Ca0.1(Mg0.4Al1.6)[Si3.9Al0.1O10](OH)2 (I), ?5614.3 ± 7.0 kJ/mol for Na0.4K0.1(Ca0.1Mg0.3Al1.5Fe 0.1 3+ )[Si3.9Al0.1O10](OH)2 (II), ?5719 ± 11 kJ/mol for K0.1Ca0.2Mg0.2(Mg0.6Al1.3Fe 0.1 3+ ) [Si3.7Al0.3O10](OH)2 (III), and ?6454 ± 11 kJ/mol for water-bearing montmorillonite (I) Na0.3Ca0.1(Mg0.4Al1.6)[Si3.9Al0.1O10](OH)2 · 2.6H2O. The paper reports estimated enthalpy of formation for the smectite end members of the theoretical composition of K-, Na-, Mg-, and Ca-montmorillonite and experimental data on the enthalpy of dehydration (14 ± 2 kJ per mole of H2O) and dehydroxylation (166 ± 10 kJ per mole of H2O) for Na-montmorillonite.  相似文献   

13.
The crystal structure and chemical composition of crystals of (Mg1?x Cr x )(Si1?x Cr x )O3 ilmenite (with x = 0.015, 0.023 and 0.038) synthesized in the model system Mg3Cr2Si3O12–Mg4Si4O12 at 18–19 GPa and 1,600 °C have been investigated. Chromium was found as substitute for both Mg at the octahedral X site and Si at the octahedral Y site, according to the reaction Mg2+ + Si4+ = 2Cr3+. Such substitutions cause a shortening of the <X–O> and a lengthening of the <Y–O> distances with respect to the values typically observed for pure MgSiO3 ilmenite and eskolaite Cr2O3. Although no high Cr contents are considered in the pyrolite model, Cr-bearing ilmenite may be the host for chromium in the Earth’s transition zone. The successful synthesis of ilmenite with high Cr contents and its structural characterization are of key importance because the study of its thermodynamic constants combined with the data on phase relations in the lower-mantle systems can help in the understanding of the seismic velocity and density profiles of the transition zone and the constraining composition and mineralogy of pyrolite in this area of the Earth.  相似文献   

14.
Jinshanjiangite (acicular crystals up to 2 mm in length) and bafertisite (lamellar crystals up to 3 × 4 mm in size) have been found in alkali granite pegmatite of the Gremyakha-Vyrmes Complex, Kola Peninsula. Albite, microcline, quartz, arfvedsonite, zircon, and apatite are associated minerals. The dimensions of a monoclinic unit cell of jinshanjiangite and bafertisite are: a = 10.72(2), b=13.80(2), c = 20.94(6) Å, β = 97.0(5)° and a = 10.654(6), b = 13.724(6), c = 10.863(8) Å, β = 94.47(8)°, respectively. The typical compositions (electron microprobe data) of jinshanjiangite and bafertisite are: (Na0.57Ca0.44)Σ1.01(Ba0.57K0.44)Σ1.01 (Fe3.53Mn0.30Mg0.04Zn0.01)Σ3.88(Ti1.97Nb0.06Zr0.01)Σ2.04(Si3.97Al0.03O14)O2.00(OH2.25F0.73O0.02)Σ3.00 and (Ba1.98Na0.04K0.03)Σ2.05(Fe3.43Mn0.37Mg0.03)Σ3.83(Ti2.02Nb0.03)Σ2.05 (Si3.92Al0.08O14)(O1.84OH0.16)Σ2.00(OH2.39F1.61)Σ3.00, respectively. The minerals studied are the Fe-richest members of the bafertisite structural family.  相似文献   

15.
Fault affecting silicoclastic sediments are commonly enriched in clay minerals. Clays are sensitive to fluid–rock interactions and deformation mechanisms; in this paper, they are used as proxy for fault activity and behavior. The present study focuses on clay mineral assemblages from the Point Vert normal fault zone located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep in SE France. In this area, the Annot sandstones were buried around 6–8 km below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The fault affects arkosic sandstone beds alternating with pelitic layers, and displays throw of about thirty meters. The fault core zone comprises intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The foliated sandstones display clay concentration along S–C structures characterized by dissolution of K-feldspar and their replacement by mica, associated with quartz pressure solution, intense microfracturation and quartz vein precipitation. The gouge is formed by a clayey matrix containing fragments of foliated sandstones and pelites. However, a detailed petrographical investigation suggests complex polyphase deformation processes. Optical and SEM observations show that the clay minerals fraction of all studied rocks (pelites and sandstones from the damage and core zones of the fault) is dominated by white micas and chlorite. These minerals have two different origins: detrital and newly-formed. Detrital micas are identified by their larger shape and their chemical composition with a lower Fe–Mg content than the newly-formed white micas. In the foliated sandstones, newly-formed white micas are concentrated along S–C structures or replace K-feldspar. Both types of newly formed micas display the same chemical composition confirmed microstructural observations suggesting that they formed in the same conditions. They have the following structural formulas: Na0.05 K0.86 (Al 1.77 Fe0.08 Mg0.15) (Si3.22 Al0.78) O10 (OH)2. They are enriched in Fe and Mg compared to the detrital micas. Newly-formed chlorites are associated with micas along the shear planes. According to microprobe analyses, they present the following structural formula: (Al1,48 Fe2,50 Mg1,84) (Si2,82 Al1,18) O10 (OH)8. All these data suggest that these clay minerals are synkinematic and registered the fault activity. In the gouge samples, illite and chlorite are the major clay minerals; smectite is locally present in some samples.In the foliated sandstones, Kubler Index (KI) ((001) XRD peak width at half height) data and thermodynamic calculations from synkinematic chlorite chemistry suggest that the main fault deformation occurred under temperatures around 220 °C (diagenesis to anchizone boundary). KI measured on pelites and sandstones from the hanging and footwall, display similar values coherent with the maximal burial temperature of the Annot sandstones in this area. The gouge samples have a higher KI index, which could be explained by a reactivation of the fault at lower temperatures during the exhumation of the Annot sandstones formation.  相似文献   

16.
The thermally induced reductive decomposition of a natural near end-member almandine [VIII(Fe2.85Mg0.11Ca0.05Mn0.02)VI(Al1.99)IV(Si2.99)O12] and possible hydrogen diffusion into its structure have been carried out at temperatures up to 1,200°C, monitored by simultaneous thermogravimetric analysis and differential scanning calorimetry (DSC), infrared and 57Fe Mössbauer spectroscopy and X-ray powder diffraction. Below 1,000°C, evidence for hydrogen diffusion into almandine structure was not observed. At temperatures above 1,000°C, reductive decomposition sets in, as displayed by a sharp endothermic peak at 1,055°C on the DSC curve accompanied by a total mass loss of 3.51%. We observe the following decomposition mechanism: almandine + hydrogen → α-Fe + cristobalite + hercynite + water. At higher temperatures, fayalite and sekaninaite are formed by consecutive reaction of α-Fe with cristobalite and water, and cristobalite with hercynite, respectively. The metallic α-Fe phase forms spherical and isolated particles (~1 μm).  相似文献   

17.
The results of thermochemical studies are reported for nontronite samples from the Pinares-de-Majari (Eastern Cuba) (Sample I) and Kempirsai serpentine massif (South Urals, Kazakhstan) (Sample II). The enthalpies of formation of dehydrated hydroxyl-bearing nontronites from elements were determined by melt dissolution calorimetry using high-temperature heat-flux Tiana-Calvet microcalorimeter: Δ f H el o (298.15 K): ?4958 ± 13 kJ/mol for Mg0.4(Fe 1.5 3+ Mg0.4Ni0.1)[Si3.7Al0.3O10](OH)2 (I) and ?5003.6 ± 8.0 kJ/mol for Mg0.3Na0.1Ca0.1(Fe 1.4 3+ Mg0.5Ni0.1)[Si3.7Al0.3O10](OH)2 (II). It was determined experimentally that the enthalpy of dehydration (removal of molecular adsorption and interlayer water) of the studied nontronites is 6 ± 2 kJ per 1 mole H2O. The enthalpy of formation of nontronite of theoretical composition Mg0.15Fe 2 3+ [Si3.7Al0.3]O10(OH)2 was estimated at ?4750 kJ/mol. The Gibbs free energies of formation of the nontronites were calculated.  相似文献   

18.
高平  张流 《地质科学》1982,(3):299-308
近几年来,Y.塔达等人[3-7]建立了一种预测化合物吉布斯生成自由能的经验方法。  相似文献   

19.
A detailed study of the chemical composition and substitutions in calcium tourmalines from a scapolite-bearing rare-metal pegmatite vein from the Sol’bel’der River basin has shown that their species attribution is determined by occupancy of octahedral site Y. The composition of the yellow tourmaline most abundant in the central part of the pegmatite bodyis rather constant and characterized by the ideal formula Ca(Mg2Li)Al6(Si6O18)(BO3)3(OH)3F. Variations in the chemical composition of zonal tourmaline crystals from the contact part of the pegmatite are controlled by abrupt change in the chemical medium during their formation. The yellow cores of these crystals are close in composition to tourmaline from the central part of the pegmatite vein. The Mg content abruptly decreases toward the crystal margin: Mg2+ → Fe2+, 2Mg2+ → Li+ + Al3+, and Mg2+ + OH → Al3+ + O2−. The composition of dark green marginal zones in tourmaline is characterized by the ideal formula Ca(Al1.5Li1.5)Al6(Si6O18)(BO3)3 (OH2O)(F). The results indicate specific formation conditions of pegmatite. The crystallochemical formulas of the studied tourmalines allow us to regard them as new mineral species in the tourmaline group.  相似文献   

20.
Sudoite, the di-trioctahedral chlorite with ideal composition (Mg2Al)(Al2)(Si3Al)O10(OH)8 is a widespread rock-forming mineral in meta-siltstones and psammites of the Verrucano sequence of the Northern Apennines. Sub-ellipsoidal aggregates, probably derived from muscovite clasts, consisting of sudoite, pyrophyllite and muscovite, are common; sudoite may also occur as thin blades in the rock matrix. The co-existence of sudoite, Ferich chloritoid and pyrophyllite, reported here for the first time, has been observed in specimens from the M. Argentario and Monticiano-Roccastrada areas. This three-phase assemblage, diagnostic of a specific metamorphic facies, may be a tool for detailed zonation of low-grade terranes.  相似文献   

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