Corrensite and mixed-layer chlorite/corrensite in metabasalt from northern Taiwan: TEM/AEM,EMPA, XRD,and optical studies     

Yen-Hong Shau  Donald R. Peacor  Eric J. Essene 《Contributions to Mineralogy and Petrology》1990,105(2):123-142

Many chloritic minerals in low-grade metamorphic or hydrothermally altered mafic rocks exhibit abnormal optical properties, expand slightly upon glycolation (expandable chlorite) and/or have excess Al^VI relative to Al^IV, as well as significant Ca, K and Na contents. Chloritic minerals with these properties fill vesicles and interstitial void space in low-grade metabasalt from northern Taiwan and have been studied with a combination of TEM/AEM, EMPA, XRD, and optical microscopy. The chloritic minerals include corrensite, which is an ordered 1:1 mixed-layer chlorite/smectite, and expandable chlorite, which is shown to be a mixed-layer chlorite/corrensite. Corrensite and some mixed-layer chlorite/corrensite occur as rims of vesicles and other cavities, while later-formed mixed-layer chlorite/corrensite occupies the vesicle cores. The TEM observations show that the mixed-layer chlorite/corrensite has ca. 20%, and the corrensite has ca. 50% expandable smectite-like layers, consistent with XRD observations and with their abnormal optical properties. The AEM analyses show that high Si and Ca contents, high Al^VI/Al^IV and low Fe^VI/(Fe+Mg)^VI ratios of chlorites are correlated with interstratification of corrensite (or smectite-like) layers in chlorite. The AEM analyses obtained from 200–500 Å thick packets of nearly pure corrensite or chlorite layers always show that corrensite has low Al^IV/Si^IV and low Fe^VI/(Fe+Mg)^VI, while chlorite has high Al^IV/Si^IV and high Fe^VI/(Fe+Mg)^VI. This implies that the trioctahedral smectite-like component of corrensite has significantly lower Al^IV/Si^IV and Fe^VI/(Fe+Mg)^VI. The ratios of Fe^VI/(Fe+Mg)^VI and Al^IV/Si^IV thus decrease in the order chlorite, corrensite, smectite. The proportions of corrensite (or smectite-like) layers relative to chlorite layers in low-grade rocks are inferred to be controlled principally by Fe/Mg ratio in the fluid or the bulk rock and by temperature. Compositional variations of chlorites in low-grade rocks, which appear to correlate with temperature or metamorphic grade, more likely reflect variable proportions of mixed-layered components. The assemblages of trioctahedral phyllosilicates tend to occur as intergrown discrete phases, such as chlorite-corrensite, corrensite-smectite, or chlorite-corrensite-smectite. A model for the corrensite crystal structure suggests that corrensite should be treated as a unique phase rather than as a 1:1 ordered mixed-layer chlorite/smectite.  相似文献   

The relation between c dimension and exchange components in micas     

Embaie Asmerom Ferrow 《Mineralogy and Petrology》1990,43(1):23-35

Summary A number of micas of varying compositions and polytypism have been selected from the literature for multiple linear regression analysis. The c dimension in micas is found to depend on the sizes of the interlayer cation, d_i, and tetrahedral cation, d_t, as well as on the hydroxyl content, [OH]. The regression equation obtained: c_r = 5.415 + 0.071[OH] + 2.098d_i + 2.335d_t with R² = 90.5%, shows that the three variables affect the c-axis dimension in the order d_t > d_i [OH]. Addition of 2- and 3-layer polytypes to the regression analysis reduces R² to 87.2%. Application of the regression analysis to synthetic Al-rich biotites from the literature shows that the amount of [A1^IVA1^VI]_1Y[Fe²⁺, MgSi]_–1y in solid solution is limited and always less than [A1^VIO]_1z[Fe²⁺, MgOH]_–1z (i.e. 0.35 > y z). The maximum value of the vector y in solution is slightly higher than that reported for natural Al-rich biotites.

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Die Beziehung zwischen der Gitterkonstante c und den Austauschkomponenten in Glimmern

Zusammenfassung Eine Anzahl von Glimmern unterschiedlicher Zusammensetzung und Polytypie wurde aus der Literatur für eine multiple lineare Regressionsanalyse ausgewählt. Es stellte sich heraus, dass in Glimmern die Gitterkonstante c von den Grössen des Zwischenschicht-Kations d_i und des tetraedrischen Kations d_t abhängt, ferner vorn Hydroxylgehalt, [OH]. Die erhaltene Regressionsgleichung c_r = 5,415 + 0,071 [OH] + 2,098d_i + 2,335d_t mit R² = 90,5% zeigt, dass die drei Variablen die Grösse der c-Achse in der Reihenfolge d_t > d_i [OH] beeinflussen. Der Einschluss von 2- und 3-Schicht Polytypen in die Regressionsanalysen verkleinert R² auf 87,2%. Die Anwendung der Regressionsanalysen auf synthetische Al-reiche Biotite aus der Literatur zeigt, der Betrag von [A1^IVA1^VI]_1y[Fe²⁺, MgSi]_–1y beschränkt und immer kleiner als [A1^VIO]_1z[Fe²⁺, MgOH]_–1z (mit 0,35 < y z) ist. Der Maximalwert des Vektors y in Lösung ist etwas grösser als jener, der für natürliche Al-reiche Biotite angegeben wurde.

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With 1 Figure  相似文献   

The CaGeO3–Ca3Fe2Ge3O12 garnet join: an experimental study     

Gianluca Iezzi  Tiziana Boffa-Ballaran  Catherine McCammon  Falko Langenhorst 《Physics and Chemistry of Minerals》2005,32(3):197-207

Germanate garnets are often used as isostructural analogues of silicate garnets to provide insight into the crystal chemistry and symmetry of the less accessible natural garnet solid solutions. We synthesised two series of germanate garnets at 3 GPa along the join^VIIICa₃^VI(CaGe)^IVGe₃O₁₂–^VIIICa₃^VIFe₂^IVGe₃O₁₂ at 900 °C and 1,100 °C. Samples with compositions close to the CaGeO₃ end-member consist of tetragonal garnet with a small amount of triclinic CaGe₂O₅. Samples with nominal compositions between X_Fe=0.4 and 1.0 consist of a mixture of tetragonal and cubic garnets; whereas, single-phase cubic garnets were obtained for compositions with X_Fe>1.2 (X_Fe gives the iron content expressed in atoms per formula unit, and varies between 0 and 2 along the join). Run products which were primarily single-phase garnet were investigated using Mössbauer spectroscopy. Spectra from samples synthesised at 1,100°C consist of one well-resolved doublet that can be assigned to Fe³⁺ in the octahedral site of the garnet structure. A second doublet, present primarily in samples synthesised at 900°C, can be assigned to Fe²⁺ at the octahedral sites of the garnet structure. The relative abundance of Fe²⁺ decreases with increasing iron content. Transmission electron microscopy analyses confirm this tendency and show that the garnets are essentially defect-free. The unit-cell parameters of tetragonal ^VIIICa₃^VI(CaGe)^IVGe₃O₃ garnet decrease with increasing synthesis temperature, and the deviation from cubic symmetry becomes smaller. Cubic garnets show a linear decrease of unit-cell parameter with increasing iron content. The results are discussed in the context of iron incorporation into ^VIIIMg₃^VI(MgSi)^IVSi₃O₃ majorite.  相似文献   

Chemical variation in vesuvianite     

S. Fitzgerald  P. B. Leavens  J. A. Nelen 《Mineralogy and Petrology》1992,46(2):163-178

Summary Microprobeanalyses of 44 vesuvianite specimens of different color, morphology, and occurrence indicate the chemical variation of the species. Vesuvianites can be divided into four types, based on chemistry and color; most vesuvianites can be assigned to one of these types with confidence. Type 1 vesuvianites contain 2 atoms of Mg, <0.25 atoms of Ti, and variable Fe, apparently trivalent, in a formula based on 50 non-H cations. They are dark to pale green, white, or pink. Type 2 vesuvianites contain > 2.5 atoms of Mg, variable (divalent?) Fe, and <0.5 atoms of Ti. In color they are yellow, yellow-brown, or yellow-green. Type 3 vesuvianites contain divalent Fe, 0.5 to 1.5 atoms of Ti and close to 18 atoms of Si (full occupancy of tetrahedral sites). They are yellow, brown, red-brown, or black. Type 4 vesuvianites are manganoan or cuprian; the studied samples are from Pajsberg, Sweden, Franklin, New Jersey, and Telemark, Norway. In color they are red-brown, purple, blue (cyprine), or green. Iron and much of the Mn is apparently trivalent.Unlike garnets, which they resemble structurally, vesuvianites contain almost exclusively Ca in the eight-fold sites in the structure. Silicon occupies 95% or more of the tetrahedral sites. Aluminum fills the smaller octahedral site, A. Chemical variation occurs predominantly in the more open, octahedral, general or G site and in the five-coordinated B site. Simple substitutions in G include Fe³⁺ or Mn³⁺ for Al³⁺, and Fe²⁺, Mn²⁺, or Zn²⁺ for Mg²⁺. Coupled substitutions include TiO = AIOH, MgTi = AlAl and AlAl = MgSi. The B site may contain Cue²⁺, Fe²⁺, Fe³⁺, or A1³⁺. Changes in the amounts of O and OH in two different positions give a range of anion charge from 146 (0₆₇0H₁₂) to about 148 (0₆₉0H₁₀).

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Chemische variation in Vesuvianen

Zusammenfassung Mikrosondenanalysen von 44 Vesuvian-Proben, die in Farbe, Morphologie and Vorkommen unterschiedlich sind, zeigen die chemische Variation der Spezies. Aufgrund von Chemismus und Farbe können Vesuviane in vier Typen eingeteilt werden; die meisten Vesuviane konnen einem dieser Typen klar zugeordnet werden. Vesuviane vom Typ 1 enthalten in einer Formel, die sich auf 50 nicht-H Kationen bezieht, 2 Mg-Atome, < 0,25 Ti-Atome and variables, anscheinend dreiwertiges Fe. Sie sind dunkel- bis blaßgrün, weiß oder rosa. Vesuviane vom Typ 2 enthalten > 2,5 Mg-Atome, variables (zweiwertiges?) Fe and < 0,5 Ti-Atome. Sie sind gelb, gelbbraun oder gelbgrün gefärbt. Vesuviane vom Typ 3 enthalten zweiwertiges Fe, 0,5 bis 1,5 Ti-Atome and beinahe 18 Si-Atome (völlige Besetzung der Tetraederpositionen). Sie sind gelb, braun, rotbraun oder schwarz. Vesuviane vom Typ 4 sind Mangan- oder Kupfer-haltig; die untersuchten Proben sind von Pajsberg, Schweden, Franklin, New Jersey, and Telemark, Norwegen. Sie sind rotbraun, purpur, blau (Cyprin) oder grün gefarbt. Eisen und ein großer Teil des Mangns sind anscheinend dreiwertig.Im Unterschied zu den strukturell ähnlichen Granaten enthalten die Vesuviane auf den acht-koordinierten Positionen der Struktur fast nur Ca. Silizium besetzt 95% oder mehr der Tetraederpositionen. Aluminium füllt die kleinere Oktaederposition A. Chemische Variabilität tritt hauptsächlich in der offeneren, oktaedrischen, allgemeinen oder G Position and in der fiinf-koordinierten B Position auf. Einfache Substitutionen auf G umfassen Fe³⁺ und Mn³⁺ fur Al³⁺, sowie Fe²⁺, Mn²⁺ and Zn²⁺ für Mgt²⁺. Gekoppelte Substitutionen beinhalten TiO = AlOH, MgTi = AlAl and AlAl = MgSi. Die B Position kann Cu²⁺, Fe²⁺, Fe³⁺ and A1³⁺ enthalten. Wechsel in den Beträgen an O und OH auf zwei unterschiedlichen Positionen gibt für die Anionenladung einen Bereich von 146 (O₆₇OH₁₂) bis etwa 148 (O₆₉OH₁₀).[/p]

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Spectroscopic active IVFe3+–VIFe3+ clusters in spinel–magnesioferrite solid solution crystals: a potential monitor for ordering in oxide spinels     

G. B. Andreozzi  U. Hålenius  H. Skogby 《Physics and Chemistry of Minerals》2001,28(7):435-444

Optical absorption spectra (OAS) of synthetic single crystals of the solid solution spinel sensu stricto (s.s.)–magnesioferrite, Mg(Fe³⁺Al_1???y)₂O₄ (0?y?≤ 0.3), have been measured between 12 500 and 28 500?cm^?1. Chemical composition and Fe³⁺ site distribution have been measured by electron microprobe and Mössbauer spectroscopy, respectively. Ferric iron is ordered to the tetrahedral site for samples with small magnesioferrite component, and this ordering is shown to increase with magnesioferrite component. The optical absorption spectra show a strong increase in band intensities with Fe³⁺→Al substitution. Prominent and relatively sharp absorption bands are observed at 25 300 and 21 300?cm^?1, while less intense bands occur at 22 350, 18 900, 17 900 and 15 100?cm^?1. On the basis of band energies, band intensities and the compositional effect on band intensity, as well as structural considerations, we assign the observed bands to electronic transitions in ^IVFe³⁺–^VIFe³⁺clusters. A linear relationship (R ²= 0.99) between the α_net value of the absorption band at 21 300?cm^?1 and [^IVFe³⁺]?·?[^VIFe³⁺] concentration product has been defined: α_net=2.2?+?15.8 [^IVFe³⁺]?·?[^VIFe³⁺]. Some of the samples have been heat-treated between 700 and 1000?°C to investigate the relation between Fe³⁺ ordering and absorption spectra. Increase of cation disorder with temperature is observed, which corresponds to a 4% reduction in the number of active clusters. Due to the high spatial resolution (??～?10?μm), the OAS technique may be used as a microprobe for determination of Fe³⁺ concentration or site partitioning. Potential applications of the technique include analysis of small crystals and of samples showing zonation with respect to total Fe³⁺ and/or ordering.  相似文献   

Crystal chemical variations in Ba-rich biotites from gabbroic rocks of lower crust (Ivrea Zone,NW Italy)     

Simona Bigi  Maria Franca Brigatti  Maurizio Mazzuchelli  Giorgio Rivalenti 《Contributions to Mineralogy and Petrology》1993,113(1):87-99

Biotites from mafic rocks occurring at different stratigraphic levels of the Ivrea-Verbano Mafic Complex are studied. The rocks are gabbros and diorites. All the biotites are intermediate between phlogopite and annite [0.282 (up to 7.14 and 9.32 wt%, respectively) with respect to those of the diorites (up to 1.26 and 6.26 wt%, respectively). Systematic compositional variations support the substitution model 2 ^IV Si+( ^IV R²⁺)2 ^IV Al+ ^VI Ti (R²⁺=Fe+Mg+Mn) in gabbros and ^IV Si+ ^VI Al ^IV Al+ ^VI Ti in diorites. A predominance of disordered stacking sequences, coexisting with 1M, 2M ₁ and 3T polytypes was observed in all biotites. It was possible to carry out structural refinements only on three biotites-2M ₁ from diorites (R-values between 2.68 and 3.77) and one biotite-1M from gabbros (R-value=3.09). It was shown that: (1) the reduced thickness of the tetrahedral sheet in Ba-rich biotites supports the coupled substitution ^IV Si+ ^XII K ^IV Al+ ^XII Ba; (2) the interlayer site geometry is affected by the whole layer chemistry and does not reflect only local chemical variations; (3) in two samples of the 2M ₁ polytype, the M(1) octahedral site is larger and more distorted than the M(2) sites because of the preferential ordering of Fe²⁺ in the M(1) site, whereas one sample shows complete cation disorder in the octahedral sites. Biotite-1M shows that Fe²⁺ can also be located in the M(2) site. Some of the differences between the biotites of gabbros and diorites (e.g. Ba concentration and exchange vectors) may be linked to the host rock composition and to its crystallization process. Biotite occurs in trace amounts in gabbros and its crystallization is related to the interstitial melt which contributed to the adcumulus growth of the main rock forming phases and became highly enriched in K, Ba and Ti. Diorites are the result of equilibrium crystallization of a residual melt rich in incompatible elements, where biotite is a major constituent.  相似文献   

The effect of composition,temperature and pressure on the stability of the 1Tc and 2M polytypes of sapphirine     

Andrew G. Christy 《Contributions to Mineralogy and Petrology》1989,103(2):203-215

Microprobe analyses and structural characterisation by means of transmission electron microscopy and powder X-ray diffraction are presented for a suite of natural and synthetic sapphirines. Most sapphirines appear to consist of intergrowths of the common 2M polytype with minor amounts of the 1Tc phase, although the converse situation is found in some cases. Attempts to correlate the structural state of the mineral with other factors reveal that: (i) There is no strong relationship between mean tetrahedral cation radius or mean octahedral cation radius and the preferred polytype. The Tschermak substitution M²⁺M⁴⁺-M³⁺M³⁺ does not appreciably influence the 1Tc-2M equilibrium, (ii) However, the total content and mean oxidation state of iron in sapphirine are important in this respect. Fe²⁺ stabilises the 2M phase, whereas Fe³⁺ stabilises the 1Tc phase. (iii) P-T estimates for the host rocks, and estimates for the conditions of sapphirine crystallisation, where obtainable, suggest that the 1Tc phase is stable at lower T and higher P than the 2M phase. Some quantitative constraints are inferred.  相似文献   

ELNES spectroscopy of mixed Si coordination minerals     

B. Poe  F. Seifert  T. Sharp  Z. Wu 《Physics and Chemistry of Minerals》1997,24(7):477-487

 Si K- and L-edge ELNES spectroscopy and multiple-scattering (MS) calculations are used to examine mixed Si coordination compounds varying in Si^VI:Si^IV ratio. As in previous studies, the edges are influenced mainly by silicon coordination (tetrahedral vs. octahedral), as supported by the MS calculations. We demonstrate two methods semi-quantitatively to extract the value of Si^VI/(Si^VI+Si^IV): (1) A linear relationship between the L_2,3-L₁ splitting and Si^VI/(Si^VI+Si^IV) is observed, (2) a fitting method based on the coaddition of reference tetrahedral and octahedral Si spectra is applied to both Si K- and L-edge ELNES spectra. Received: February 10, 1997 / Revised, accepted: May 23, 1997  相似文献   

Composition of hornblendes formed during the hercynian progressive metamorphism of the Aracena metamorphic belt (SW Spain)     

J. P. Bard 《Contributions to Mineralogy and Petrology》1970,28(2):117-134

This paper attempts to illustrate the chemical variations of metamorphic hornblendes regarding host rocks and prograde variations. Changes related to bulk chemistry (orthoamphibolites) mainly concern Si, Al, Mg, Fe_tot and Ca. The Mg, Fe²⁺ and Fe³⁺ contents of hornblendes are, however, not strictly related to host rook compositions and Mg enrichments are correlated with increasing Fe³⁺ contents in the amphiboles. Thus, variations of oxygen fugacity may control the Mg contents of the Ca amphiboles studied but this does not show clear relations with the prograde metamorphism. The most sensitive but irregular variation related to the metamorphic conditions is the prograde enrichment of the alkalis into the A vacant position and an increase of the (Na+K)_tot/Na+K+Ca ratios of the amphiboles. Increasing Ti and Al^IV contents as well as decreasing Al^VI concentrations are also, but much less evidently, related to increasing T and P. A variation trend from tschermakitic to edenitic hornblendes may be drawn using Shido's end members calculation; this tendency and the relative deficiency of Al^VI contents in the low-grade members suggests that the amphiboles studied were subjected to conditions of a low-pressure metamorphism type. Such a conclusion is in agreement with the occurrence of andalusite-cordierite/sillimanite-cordierite associations in the metapelitic rocks, and the absence of Fe-rich garnet and epidote from the orthoamphibolites of the amphibolite facies at Aracena. Comparisons with Ca amphiboles from other metamorphic areas show, in agreement with various authors, that Abukuma hornblendes are similar to those encountered in high-grade thermal aureoles and tonalitic intrusives but different from the hornblendes of Barrovian metamorphism types.  相似文献   

Electronic absorption spectra of chromium-bearing sapphirine     

K. Langer  A. N. Platonov  S. S. Matsuk  M. Andrut 《Physics and Chemistry of Minerals》1994,21(1-2):29-35

Violet, non-pleochroic and greenish-blue, pleochroic chromium-substituted sapphirines were found in corundum-bearing spinel-websterite xenolites from the Yakutian kimberlite pipes Noyabrskaya (N) and Sludyanka (Sl), respectively. The crystallochemical formulae of sapphirine crystals from such xenolites were determined by EMP to be (Mg_3.40Fe_0.23Al_3.25Cr_0.16)^[6] Al _1.00 ^[6] [O₂/Al_4.53Si_1.47O₁₈] (N) and (Mg_2.53Fe_0.55 Mn_0.04Ti _0.03 ⁴⁺ Al_3.55Cr _0.08 ³⁺ )^[6]Al _1.00 ^[16] [O₂/Al_4.28Si_1.73O₁₈] (Sl). Single crystal spectra in the range 35000–6000 cm^1- showed a slightly polarization dependent absorption edge near 3200 cm^1- (N) or 30000 cm^1- (Sl) and unpolarized bands at 25300 and 17300 cm^1-, typical of spin-allowed transitions, derived from ⁴A_2g→⁴T_1g and ⁴A_2g→⁴T_2g, of Cr³⁺ in octahedral sites, with point symmetry C₁, of the structure. Another weak band at 23000 cm^?1 in the sapphirine-N spectra is attributed to low symmetry splitting of the excited ⁴T₁ (F)-State of Cr³⁺. These assignments lead to crystal field parameters Dq=1730cm^?1 and B= 685cm^?1 of Cr³⁺ in sapphirine. Crystallochemical and spectroscopic arguments suggest that Cr³⁺ subsitutes for Al in the M(1) or M(8) sites of the sapphirine structure. In addition to Cr³⁺-transitions, spectra of Sl exhibit weak dd-bands of Fe²⁺ at 10000 and 7700 cm^1-, which are unpolarized in consistency with the C₁ site symmetry of the octahedra in the structure. Spectra of Sl show also prominent, broad bands (Δv_1/2～-5000 cm^1-) at 15000 and 11000 cm^1-, which occur in E//Y(//b) and E//Z(//_c=12°) only and exhibit an intensity ratio α_Y∶α_z close to 1∶3. This result, the large half width, as well as band energy — MM distance considerations suggest that these bands originate from Fe^2+[6]-Fe^3+[6] charge-transfer transitions in wall octahedra M(1)M(2), M(6)M(7) etc., forming MM vectors of 30° with the c-axis. The lack of Fe²⁺-Fe³⁺ charge-transfer bands in sapphirine N might indicate a lower oxygen fugacity during the formation of the websterite from the Noyabrskaya pipe compared to that from the Sludyanka pipe.  相似文献   

Magnetic behavior of trioctahedral micas with different octahedral Fe ordering     

Stefano Pini  Maria Franca Brigatti  Marco Affronte  Daniele Malferrari  Augusto Marcelli 《Physics and Chemistry of Minerals》2012,39(8):665-674

This contribution is finalized at the discussion of the magnetic structure of two samples, belonging to phlogopite–annite [sample TK, chemical composition ^IV(Si_2.76Al_1.24) ^VI(Al_0.64Mg_0.72 $ {\text{Fe}}_{1.45}^{2 + } $ Mn_0.03Ti_0.15) (K_0.96Na_0.05) O_10.67 (OH)_1.31 Cl_0.02] and polylithionite–siderophyllite joints [sample PPB, chemical composition ^IV(Si_3.14Al_0.86)^VI(Al_0.75Mg_0.01 $ {\text{Fe}}_{1.03}^{2 + } $ $ {\text{Fe}}_{1.03}^{3 + } $ Mn_0.01Ti_0.01Li_1.09) (K_0.99Na_0.01) O_10.00 (OH)_0.65F_1.35]. Samples differ for Fe ordering in octahedral sites, Fe²⁺/(Fe²⁺?+?Fe³⁺) ratio, octahedral composition, defining a different environment around Fe cations, and layer symmetry. Spin-glass behavior was detected for both samples, as evidenced by the dependency of the temperature giving the peak in the susceptibility curve from the frequency of the applied alternating current magnetic field. The crystal chemical features are associated to the different temperature at which the maximum in magnetic susceptibility is observed: 6?K in TK, where Fe is disordered in all octahedral sites, and 8?K in PPB sample, showing a smaller and more regular coordination polyhedron for Fe, which is ordered in the trans-site and in one of the two cis-sites.  相似文献   

Nonstoichiometry in sillimanite: Mullite compositions with sillimanite-type superstructures     

W. E. Cameron 《Physics and Chemistry of Minerals》1977,1(3):265-272

Complete solid solution between sillimanite and mullite is shown to occur when Fe³⁺, in the virtual absence of Ti, replaces Al^VI. All members of the series adopt the sillimanite (Al, Si)^IV ordering scheme in preference to the modulated structure typical of synthetic and titaniferous natural mullites.  相似文献   

The crystal chemistry and mössbauer study of schorlomite     

Wu Gongbao  Mu Baolei 《Physics and Chemistry of Minerals》1986,13(3):198-205

Six schorlomite samples with TiO₂ contents varying between 9.70 and 15.34 weight percent were studied by means of Mössbauer spectroscopy and chemical analysis. The measured Mössbauer spectra have complex shapes. The spectra of these samples were fitted with six doublets, which can be assigned to ^VIIIFe²⁺, ^VIFe²⁺, ^VIFe³⁺, ^IVFe³⁺ and two electron delocalizations, ^IVFe³⁺ ? ^VIIIFe²⁺ and ^IVFe³⁺ ? ^VIFe²⁺, respectively. The assignment of iron absorption doublets and their Mössbauer parameters are discussed in terms of the single crystal structure data of one of the samples studied in this work. Cation distributions are also given. The occupancies of cations at the tetrahedral (Z) site are Fe³⁺>Al³⁺, Ti⁴⁺, and the relative enrichments at Z site are always Fe³⁺>Ti⁴⁺. Most of the six samples contain Ti³⁺. Ti³⁺/ΣTi ratios range from 1.43 percent to 6.40 percent. Fe²⁺/ΣFe ratios vary from 8.84 percent to 11.31 percent. Four types of substitution must be considered for Ti entering the garnet structure.  相似文献   

Statistical chemistry of calcic amphiboles     

Dr. S. K. Saxena  T. K. Ekström 《Contributions to Mineralogy and Petrology》1970,26(4):276-284

Principal components analysis is used to study the chemistry of 639 calcic amphiboles. Eigenvectors representing multiple partial correlation coefficients give various sets of substitutional relationships. The relative significance of each set can be noted by the percent variation of the data it represents. The highest percent variation (36%) is associated with the substitutions $$Si + Mg \rightleftharpoons Al^{IV} + Al^{VI} + Ti + Fe^{3 + } + Fe^{2 + } + Na + K$$ . Other expected substitutions among the ions such as Al^IV + Na ? Si, the positive correlation between Al^IV and Al^VI etc. are shown statistically. The substitution of Al in T ₁ and T ₂ positions imposes an ordering in the M ₁, M ₂ and M ₃ sites. Variability of OH in the amphiboles is found to be significant. There is no definite correlation between OH and Fe³⁺ but OH and Ti are positively correlated. Under certain conditions and provided the concentration of Al^IV does not change significantly, Fe and Mg may be assumed to mix ideally in the amphibole solid solution.  相似文献   

Electronic absorption spectroscopy of natural (Fe2+, Fe3+)-bearing spinels of spinel s.s.-hercynite and gahnite-hercynite solid solutions at different temperatures and high-pressures     

Michail N. Taran  Monika Koch-Müller  Klaus Langer 《Physics and Chemistry of Minerals》2005,32(3):175-188

Natural Fe²⁺, Fe³⁺-bearing spinel solid solutions from the spinel s.s.-hercynite and gahnite-hercynite series were analyzed and studied by electronic absorption spectroscopy in the spectral range 30000–3500 cm^–1 in the temperature and pressure ranges 77 T_K 600 and 10^–4 P_GPa 11.0. Two crystals were light-violet in color (type I) and six green or bluish-green (type II). The spectra of both types of spinels are dominated by an UV-absorption edge near 28000 to 24000 cm^–1, depending on the iron contents, and a very intense band system in the NIR centered around 5000 cm^–1, which is caused by spin-allowed dd-transition of tetrahedral Fe²⁺, derived from ⁵ E⁵ T₂. The strong band is in all spinels studied, split into four sub-bands, which can only be observed in very thin platelets. Between the UV-edge and the high-energy wing of the NIR-band there occur a number of very weak bands in type I spinels while the green type II spinels show some of these with significantly enhanced intensity. The intensity of the very weak bands is nearly independent from temperature. Such bands are attributed to spin-forbidden electronic transitions of ^IVFe²⁺. Temperature and pressure dependence of the intensity enhanced bands of spinels type II indicate that they are caused by ^IVFe²⁺ and ^VIFe³⁺. They are attributed to spin-forbidden transitions ⁶A_1g⁴A_1g, ⁴E_g, ⁴T_2g and ⁴T_1g of ^VIFe³⁺, the two latter being strongly intensified by exchange-coupling interaction with adjacent ^IVFe²⁺. The pressure dependence of ^IVFe²⁺ dd-band system in the NIR caused by spin-allowed ⁵ E⁵ T₂ transition noticeably differs from that of octahedral Fe²⁺, an effect which is attributed to a dynamic Jahn-Teller effect of ^IVFe²⁺ in the spinel structure.

Monika Koch-MüllerEmail: Phone: +49-331-288-1492/1402Fax: +49-331-288-1492/1402

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Crystallization trends of pyroxenes from alkaline subvolcanites of Punta delle Pietre Nere (Gargano,Southern Italy)     

Maria De Fino  L. La Volpe  G. Piccarreta 《Mineralogy and Petrology》1982,29(3):177-192

Summary The results of microprobe analyses of clinopyroxenes from alkaline melasyenites and layered melagabbros, produced by intra-plate magmatism of Paleocene age at Punta delle Pietre Nere, are here given and discussed.The analysed pyroxenes range from diopsidic to acmite-rich compositions.The first crystallized pyroxenes (diopside) show Al^VI contents suggesting shallow depths of crystallization. In addition pyroxenes from melasyenite and those from melagabbro display different Cr contents, Al/Ti and Mg/(Mg+Fe²⁺+Fe³⁺) ratios confirming their crystallization from melts produced by different parental liquids.Diopsides and salites show an overall trend towards high Al, Ti and Fe³⁺, suggesting that the crystallization occurred under decreasing SiO₂/Al₂O₃ ratios and under relatively highpH₂O–pO₂ conditions.Pyroxenes from the Pietre Nere melasyenite show a progressive variation towards acmite rich compositions at Mg/(Mg+Fe²⁺+Fe³⁺) lower than 0.5; those from the layered melagabbro, instead, show a continuous enrichment in Ca Fe³⁺ AlSiO₆. This different behaviour is due to the co-crystallization, with the latest pyroxenes, of phases with different K/Na and Si/Al ratios.

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Kristallisations-Tendenzen der Pyroxene aus Alkali-Subvulkaniten auf Punta delle Pietre Nere (Gargano, Süditalien)

Zusammenfassung Es werden die Ergebnisse der Mikrosonden-Untersuchungen von Klinopyroxenen aus Alkali-Melasyeniten und schichtigen Alkali-Melagabbros, die durch Intra-plate-Magmatismus paläozenen Alters auf Punta delle Pietre Nere entstanden sind, beschrieben und erörtert.Die untersuchten Pyroxene reichen von diopsidischen bis zu Akmit-reichen Zusammensetzungen.Die zuerst kristallisierten Pyroxene (Diopsid) zeigen Al^VI-Gehalte, die auf geringe Tiefe des Kristallisationsvorganges hinweisen. Dazu zeigen die Pyroxene aus dem Melasyenit und aus dem Melagabbro unterschiedliche Cr-Gehalte; die Al/Ti- und Mg/(Mg+Fe²⁺+Fe³⁺)-Verhältnisse bestätigen deren Kristallisation aus Schmelzen, die aus unterschiedlichen Ursprungsmagmen stammen.Die Diopside und Salite zeigen eine einheitliche Tendenz zu hohem Al-, Ti- und Fe³⁺-Gehalt; dies deutet darauf hin, daß die Kristallisation unter abnehmenden SiO₂/Al₂O₃-Verhältnissen und unter relativ hohenpH₂O–pO₂-Bedingungen stattfand.Die Pyroxene aus dem Punta delle Pietre Nere-Melasyenit zeigen eine zunehmende Änderung zu Akmit-reichen Zusammensetzungen bei weniger als 0,5 Mg/(Mg+Fe²⁺+Fe³⁺); die Pyroxene aus dem schichtig differenzierten Melagabbro zeigen dagegen eine allmähliche Zunahme von CaFe³⁺AlSiO₆. Dieses unterschiedliche Verhalten rührt daher, daß Mineralphasen mit unterschiedlichen K/Na- und Si/Al-Verhältnissen zugleich mit den zuletzt gebildeten Pyroxenen kristallisierten.

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A Stucture—mineralogical Study of Ringwoodite     

傅平秋  谢鸿森等 《中国地球化学学报》1990,9(2):99-104

The powder XRD analysis of ringwoodite(γ-Fe2SiO4),which was synthesized in a II-stage anvil high-pressure capsule,was made,Its unit-cell parameter was calculated:a=8.219A,After the refinements,for several cycles,of the oxygen parameter x and the occupancy rate of Si in octahedron site,i.e.,the iversion degree u,the final result is R=0.077,when x=0.379A and u=27.5%,with the structural formula (Fe1.725 Si0.275)VI(Si0.725Fe0.275)IV O4 and atomic distances(Fe,Si)VI-O=2.022 A and (Si,Fe)IV-O=1.836A,Meanwhile,the Moessbauer spectroscopic analysis of the sample was conducted and the results obtained are in good agreement with those of X-ray structural analysis ,This paper focuses on the phase transformation and the properties of bonds of α－Fe2SiO4→γ-Fe2SiO4.  相似文献   

Sapphirine bearing granulites from the Sipiwesk Lake area of the late Archean Pikwitonei granulite terrain,Manitoba, Canada   总被引：1，自引：0，他引：1  

Makoto Arima  Robert L. Barnett 《Contributions to Mineralogy and Petrology》1984,88(1-2):102-112

Sapphirine occurs in the orthopyroxene-cordierite and feldspar-sillimanite granulites in the Sipiwesk Lake area of the Pikwitonei granulite terrain, Manitoba (97°40W, 55°05N). The orthopyroxene-cordierite granulites have extremely high Al₂O₃ (24.5 wt%) and MgO (24.6 wt%) contents and contain sapphirine (up to 69.2 wt% Al₂O₃), aluminous orthopyroxene (up to 8.93 wt% Al₂O₃), cordierite, spinel, phlogopite, and corundum. Sapphirine forms coronas mantling spinel and corundum. Corona sapphirine is zoned and its composition varies through the substitution (Mg, Fe, Mn) Si=2 Al as a function of the phases with which it is in contact. Textural and chemical relationships of sapphirine with coexisting phases indicate that spinel + cordierite reacted to form orthopyroxene + sapphirine under conditions of increasing pressure. Moreover, decreasing core to rim variation of Al₂O₃ in orthopyroxene porphyroblasts suggests decreasing temperature during sapphirine formation. On the basis of experimentally determined P-T stability of the assemblage enstatite + sapphirine + cordierite, and the Al content of hypothetical Fe²⁺-free orthopyroxene associated with sapphirine and cordierite, metamorphic temperatures and pressures are estimated to be 860–890° C and 3.0–11.2 kbar.In the feldspar-sillimanite granulites, sapphirine occurs as a relict phase mantled by sillimanite and/or by successive coronas of sillimanite and garnet. These textural relations suggest the reaction sapphirine + garnet + quartz = orthopyroxene + sillimanite with decreasing temperature. Compositions of minerals in the assemblage garnet-orthopyroxene-sillimanite-plagioclase-quartz, indicate metamorphic P-T conditions of 780–880° C and 9±1 kb.The metamorphic conditions estimated in this study suggest that the sapphirine bearing granulites in the Sipiwesk Lake area represent Archean lower crustal rocks. Their formation might be related to the crustal thickening processes in this area as suggested by Hubregtse (1980) and Weber (1983).  相似文献   

Spectroscopic studies of synthetic and natural ringwoodite, γ-(Mg,Fe)<Subscript>2</Subscript>SiO<Subscript>4</Subscript>     

Michail N. Taran  Monika Koch-Müller  Richard Wirth  Irmgard Abs-Wurmbach  Dieter Rhede  Ansgar Greshake 《Physics and Chemistry of Minerals》2009,36(4):217-232

Synthetic ringwoodite γ-(Mg_1?x Fe _x )₂SiO₄ of 0.4 ≤ x ≤ 1.0 compositions and variously colored micro-grains of natural ringwoodite in shock metamorphism veins of thin sections of two S6-type chondrites were studied by means of microprobe analysis, TEM and optical absorption spectroscopy. Three synthetic samples were studied in addition with Mössbauer spectroscopy. The Mössbauer spectra consist of two doublets caused by ^VIFe²⁺ and ^VIFe³⁺, with IS and QS parameters close to those established elsewhere (e.g., O’Neill et al. in Am Mineral 78:456–460, 1993). The Fe³⁺/Fe_total ratio evaluated by curve resolution of the spectra, ranges from 0.04 to 0.1. Optical absorption spectra of all synthetic samples studied are qualitatively very similar as they are directly related to the iron content. They differ mostly in the intensity of the observed absorption features. The spectra consist of a very strong high-energy absorption edge and a series of absorption bands of different width and intensity. The three strongest and broadest absorptions of them are attributed to splitting of electronic spin-allowed ⁵ T _2g → ⁵ E _g transitions of ^VIFe²⁺ and intervalence charge-transfer (IVCT) transition between ferrous and ferric ions in adjacent octahedral sites of the ringwoodite structure. The spin-allowed bands at ca. 8,000 and 11,500 cm^?1 weakly depend on temperature, whilst the Fe²⁺/Fe³⁺ IVCT band at ~16,400 cm^?1 displays very strong temperature dependence: i.e., with increasing temperature it decreases and practically disappears at about 497 K, a behavior typical for bands of this type. With increasing pressure the absorption edge shifts to lower energies while the spin-allowed bands shift to higher energy and strongly decreases in intensity. The IVCT band also strongly weakens and vanishes at about 9 GPa. We assigned this effect to pressure-induced reduction of Fe³⁺ in ringwoodite. By analogy with synthetic samples three broad bands in spectra of natural (meteoritic) blue ringwoodite are assigned to electronic spin-allowed transitions of ^VIFe²⁺ (the bands at ~8,600 and ~12,700 cm^?1) and Fe²⁺/Fe³⁺ IVCT transition (~18,100 cm^?1), respectively. Spectra of colorless ringwoodite of the same composition consist of a single broad band at ca. 12,000 cm^?1. It is assumed that such ringwoodite grains are inverse (Fe, Mg)₂SiO₄-spinels and that the single band is caused by the split spin-allowed ⁵ E → ⁵ T ₂ transition of ^IVFe²⁺. Ringwoodite of intermediate color variations between dark-blue and colorless are assumed to be partly inversed ringwoodite. No glassy material between the grain boundaries in the natural colored ringwoodite aggregates was found in our samples and disprove the cause of the coloration to be due to light scattering effect (Lingemann and Stöffler in Lunar Planet Sci 29(1308), 1998).  相似文献   

An experimental investigation into the metastable formation of phosphoran olivine and pyroxene     

Joseph S. Boesenberg  Roger H. Hewins 《Geochimica et cosmochimica acta》2010,74(6):1923-1941

The formation of phosphoran olivine by crystallization from a melt was investigated experimentally using a one atmosphere furnace, using San Carlos olivine [(Mg,Fe)₂SiO₄] mixed with either iron phosphide (FeP) or magnesium pyrophosphate (Mg₂P₂O₇). Both dynamic crystallization and isothermal experiments produced phosphoran olivine as zoned single crystals and as overgrowths surrounding normal, phosphorus-free olivine grains. The crystallization pathways that form phosphoran olivine were traced and confirm that it is a metastable phase that can crystallize from a phosphorus-rich melt over timescales of hours to days. Removal of the P and equilibration of the olivine however requires weeks to months in the presence of silicate melt. Phosphoran olivine with up to 27 wt% P₂O₅ was generated and up to 69% of the Si tetrahedral sites were replaced by P. The substitution of Si by P into olivine was confirmed as 4^VIM⁺² + 2^IVSi⁺⁴ ↔ 3^VIM⁺² + 2^IVP⁺⁵ + ^VI[]. Phosphoran olivine compositions that vary from (Mg,Fe)₂SiO₄ to (Mg,Fe)_1.65[]_0.35Si_0.3P_0.7O₄ have been produced in these experiments.Phosphoran pyroxene was also generated in a few experiments and forms when phosphoran olivine reacts with either tridymite or melt. It has compositions compatible with protopyroxene, orthopyroxene, pigeonite and sub-calcic augite, and can contain up to 31.5 wt% P₂O₅. Like phosphoran olivine, it is also a metastable phase. Phosphorus replaces Si in pyroxene by the following substitution methods: 8^IVSi⁺⁴ ↔ 3^IVSi⁺⁴ + 4^IVP⁺⁵ + ^IV[] with Al entering the structure by the exchange 2^IVSi⁺⁴ ↔ ^IVAl⁺³ + ^IVP⁺⁵. Phosphoran pyroxene compositions vary from (Mg,Fe)₈Si₈O₂₄ to (Mg,Fe)₈Si₃P₄[]O₂₄.  相似文献