A multi-analytical study of the crystal structure of unusual Ti–Zr–Cr-rich Andradite from the Maronia skarn, Rhodope massif, western Thrace, Greece     

A. Katerinopoulou  A. Katerinopoulos  P. Voudouris  A. Bieniok  M. Musso  G. Amthauer 《Mineralogy and Petrology》2009,95(1-2):113-124

Unusual Ti–Cr–Zr-rich garnet crystals from high-temperature melilitic skarn of the Maronia area, western Thrace, Greece, were investigated by electron-microprobe analysis, powder and single-crystal X-ray diffraction, IR, Raman and Mössbauer spectroscopy. Chemical data showed that the garnets contain up to 8 wt.% TiO₂, 8 wt.% Cr₂O₃ and 4 wt.% ZrO₂, representing a solid solution of andradite (Ca₃Fe³⁺ ₂Si₃O₁₂ ≈46 mol%), uvarovite (Ca₃Cr₂Si₃O₁₂ ≈23 mol%), grossular (Ca₃Al₂Si₃O₁₂ ≈10 mol%), schorlomite (Ca₃Ti₂[Si,(Fe³⁺,Al³⁺)₂]O₁₂ ≈15 mol%), and kimzeyite (Ca₃Zr₂[Si,Al₂]₃O₁₂ ≈6 mol%). The Mössbauer analysis showed that the total Fe is ferric, preferentially located at the octahedral site and to a smaller extent at the tetrahedral site. Single-crystal XRD analysis, Raman and IR spectroscopy verified substitution of Si mainly by Al³⁺, Fe³⁺ and Ti⁴⁺. Cr³⁺ and Zr⁴⁺ are found at the octahedral site along with Fe³⁺, Al³⁺ and Ti⁴⁺. The measured H₂O content is 0.20 wt.%. The analytical data suggest that the structural formula of the Maronia garnet can be given as: (Ca_2.99Mg_0.03)_Σ=3.02(Fe³⁺ _0.67Cr_0.54Al_0.33Ti_0.29Zr_0.15)_Σ=1.98(Si_2.42Ti_0.24Fe_0.18Al_0.14)_Σ=2.98O₁₂OH_0.11. Ti-rich garnets are not common and their crystal chemistry is still under investigation. The present work presents new evidence that will enable the elucidation of the structural chemistry of Ti- and Cr-rich garnets.  相似文献   

Pyroxene mineral chemistry of the Jinchuan intrusion,China     

G. Chai  A. J. Naldrett 《Mineralogy and Petrology》1994,51(1):1-20

Summary Chemical compositions of orthopyroxene and clinopyroxene from the Jinchuan ultramafic intrusion have been obtained by electron microprobe analysis. The Mg number (MgO/(MgO + FeO)) for both pyroxenes falls within narrow ranges, 82–87 for clinopyroxene and 81–85.5 for orthopyroxene, suggesting limited magma differentiation in regard to the present igneous body. The Al₂O₃ content ranges from 2.44 wt.% to 4.43 wt.% and increases with decreasing Mg of the pyroxenes, i.e., with the more evolved magma. This is attributed to the relatively greater effects of Al₂O₃, TiO₂, Cr₂O₃ and Fe₂O₃ than that of SiO₂ on pyroxene crystallization.Negative linear relationships between Ti⁴⁺ and Si⁴⁺, and Al³⁺ and Si⁴⁺ characterize the pyroxenes. In clinopyroxene, regression of Si⁴⁺ versus Al³⁺ results in a straight line with a slope of –1.012, indicating that the decrease of Si⁴⁺ in the crystal structure is matched by an increase only in tetrahedral Al³⁺; octahedral Al³⁺ has remained relatively constant. The negative linear relationship between Ti⁴⁺ and Si⁴⁺ in clinopyroxene reflects either a greater tendency of Ti⁴⁺ to occupy octahedral sites than Al³⁺, or that replacement of Al³⁺ for Si⁴⁺ demands a more efficient charge balance. The scatter in plots of Ti⁴⁺ versus Si⁴⁺ for orthopyroxene indicates that charge balance is not as critical as structure symmetry.The crystallization temperature of pyroxene is calculated to be 1108–1229°C usingWood andBanno's (1973) two pyroxene thermometer, and is within 40°C of that calculated fromWells's (1977) thermometer. The distribution coefficient (Kd) for Mg²⁺ and Fe²⁺ between clinopyroxene and orthopyroxene is estimated to be 0.86, which is higher than that of the other intrusions and lower than that of mantle nodules, but still falls within their Kd-1/T trend. This suggests that the Kd value of pyroxene is controlled mainly by temperature.

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Mineralchemie der Pyroxene der Jinchuan-Intrusion, China

Zusammenfassung Die chemische Zusammensetzung von Orthopyroxenen und Klinopyroxenen aus der ultramafischen Jinchuan Intrusion wurden mit der Mikrosonde bestimmt. Die Mg-Zahl (MgO/(MgO + FeO)) beider Pyroxene liegt innerhalb enger Grenzen, 82–87 für Klinopyroxen und 81–85.5 für Orthopyroxen. Dies weist auf beschränkte magmatische Differentiation der Intrusion hin. Der Al₂O₃-Gehalt liegt zwischen 2.44 Gew.%. und 4.43 Gew.%. und nimmt mit der abnehmenden Mg-Zahl der Pyroxene ab, d.h. mit dem mehr entwickelten Magma. Dies wird damit erklärt, daß Al₂O₃, TiO₂, Cr₂O₃ und Fe₂O₃ einen größeren Einfluß auf die Kristallisation der Pyroxene ausüben als SiO₂.Die Pyroxene werden durch negative lineare Beziehungen zwischen Ti⁴⁺ und Si⁴⁺, sowie Al³⁺ und Si⁴⁺ charakterisiert. In Klinopyroxenen resultiert die Regression von Si⁴⁺ gegen Al³⁺ in einer geraden Linie mit einer Neigung von –1.012. Dies weist darauf hin, daß die Abnahme der Si⁴⁺ Gehalte in die Kristallstruktur durch Zunahme von ausschliesslich tetraedrischem Al³⁺ kompensiert wird; oktaedrisches Al³⁺ ist relativ konstant geblieben. Die negative lineare Beziehung zwischen Ti⁴⁺ und Si⁴⁺ in Klinopyroxenen geht entweder auf eine stärkere Tendenz des Ti₄O₂, oktaedrische Plätze zu besetzen zurück, oder darauf daß ein Ersatz von Al³⁺ für Si⁴⁺ einen effizienteren Ladungsausgleich verlangt. Die unregelmäßige Verteilung der Plots von Ti⁴⁺ gegen Si⁴⁺ in Orthopyroxenen läßt erkennen, daß Ladungsausgleich hier nicht so kritisch ist wie die Symmetrie der Struktur.Die Kristallisationstemperatur der Pyroxene wurde mit dem Zwei Pyroxenthermometer nachWood undBanno (1973) mit 1108–1229°C bestimmt. Diese Werte liegen innerhalb von 40°C des vonWells (1977) berechneten. Der Verteilungskoeffizient (Kd) für Mg²⁺ und Fe²⁺ zwischen Klinopyroxen und Orthopyroxen wird auf 0.86 berechnet; das ist höher als der aus anderen Intrusionen und niedriger als der von Mantelxenolithen, fällt aber immer noch innerhalb des Kd-1/T Trends derselben. Dies legt den Gedanken nahe, daß der Kd Wert der Pyroxene hauptsächlich durch Temperatur bestimmt wird.

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With 6 Figures  相似文献   

Der Titan-Zirkon-Granat aus den Kalksilikatfels-Einschlüssen des Gabbro im Radautal,Harz, Bundesrepublik Deutschland     

Prof. Dr. S. Koritnig  Dr. H. Rösch  Dr. A. Schneider  Prof. Dr. F. Seifert 《Mineralogy and Petrology》1978,25(4):305-313

Zusammenfassung Die chemische Zusammensetzung eines Ti–Zr-Granats (Schorlomit) mit bis zu 32 Mol.-% Kimzeyit-Komponente wurde zusätzlich zu den chemischen Analysen mittels Mössbauer-Spektrum auf die Fe²⁺/Fe³⁺-Verteilung im Granat untersucht. Der Granat hat folgende Zusammensetzung: (Ca_2,85Na_0,01Mg_0,1Mn_0,004Y_0,001)_2,97(Zr_0,542 Ti_0,68 Al_0,065Fe _0,41 ³⁺ Fe _0,05 ²⁺ Mg_0,246Cr_0,003)_2,0(Si_2,002Al_0,556Ti_0,163Fe _0,240 ²⁺ Fe _0,029 ³⁺ )_3,0O₁₂. Die Dichte beträgt 3,85 g·cm^–3, die Brechzahln=1,92. Die Röntgendiffraktometer-Peaks sind aufgespalten ina ₀=1,229 und 1,225 nm. Der Granat stammt aus Kalksilikatfels-Einschlüssen im Gabbro des Radautals, Harz.

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The titanium-zirconium garnet of calc-silicate rock inclusions of the gabbro of Radautal, Harz Mountains, F.R.G.

Summary The chemical composition of a Ti–Zr-garnet (schorlomite) with up to 32 mol-% kimzeyite component was investigated additionally to chemical analyses by means of the Mössbauer spectrum for the Fe³⁺/Fe²⁺ distribution in the garnet. The composition is: (Ca_2,85Na_0.01 Mg_0.1Mn_0.004Y_0.001)_2.97(Zr_0.542Ti_0.68Al_0.065Fe _0.41 ³⁺ Fe _0.05 ²⁺ Mg_0.246Cr_0.003)_2.0(Si_2.002 Al_0.556Ti_0.163Fe _0.240 ²⁺ Fe _0.029 ³⁺ )_3.0O₁₂. Spec. gr. 3.85 g·cm^–3,n=1.92. The x-ray peaks are splitted witha ₀=1.229 and 1.225 nm. The garnet occurs in calc-silicate rock inclusions of the gabbro of Radautal, Harz Mountains, F. R. G.

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Mit 2 Abbildungen

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Herrn Prof. Dr.H. Meixner zur Erreichung seines 70. Lebensjahres gewidmet.  相似文献   

The Al (Nb,Ta) Ti(in−2) substitution in titanite: the emergence of a new species?     

P. Černý  M. Novák  R. Chapman 《Mineralogy and Petrology》1995,52(1-2):61-73

Summary The highest (Nb, Ta) content ever encountered in titanite is reported from the Maríkov 11 pegmatite in northern Moravia, Czech Republic. This dike is a member of a pegmatite swarm of the beryl-columbite subtype, metamorphosed under conditions of the amphibolite facies. The pegmatite carries, i.a., rare tantalian rutile intergrown with titanian ixiolite, titanian columbite-tantalite, fersmite and microlite. Fissures generated in the Nb, Ta oxide minerals during deformation are filled with titanite, formed by reaction of the oxide minerals with metamorphic pore fluids. The titanite displays limited degrees of substitutions Na(Ta > Nb)(CaTi)_–1, (Ta > Nb)₄Ti_–4Si_–1 and AI(OH, F)(TiO)_–1, but an extensive (and occasionally the sole significant) substitution (Al > Fe³⁺)(Ta > Nb)Ti_–2, responsible for widespread oscillatory zoning. This substitution reduces the proportion of the titanite componentsensu stricto, CaTiSiO₄,O, to less than 50 mole % in many analyzed spots. The extreme composition corresponds to (Ca_0.994Na_0.011)(Ti_0.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). However, so far this substitution fails to generate compositions that would define a new species.

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Zusammenfassung Die AI(Nb, Ta)Ti_–2 Substitution im Titanit: Auftauchen einer neuen Mineralspecies? Die höchsten (Nb, Ta) Gehalte, die jemals für Titanit gefunden wurden, werden für den Maríkov II Pegmatit in Nordmähren, Tschechei, berichtet. Der Intrusivgang ist Teil eines Amphibolit-faziell überprägten Pegmatitschwarms vom Beryll-Columbit Subtypus Der Pegmatit führt u.a. seltene tantalbetonte Rutile verwachsen mit titanbetontem Ixiolith, titanbetontem Columbit-Tantalit, Fersmit and Mikrolith. Deformationsbedingte Frakturen in den (Nb, Ta) Oxiden sind mit Titanit, als Folge der Reaktion der metamorphen Porenlösungen mit den Oxidmineralen, verkittet. Titanit zeigt begrenzte Substitutionen Na(Ta > Nb)(CaTi)_–1,(Ta > Nb)₄Ti_–4Si_–1 and Al(OH, F)(TiO)_–1, aber extensive (und gelegentlich einzig bedeutsame) Substitution (Al >> Fe³⁺)(Ta > Nb)Ti_–2, die eine weitverbreitete, oszillierende Zonierung hervorruft. Diese Substitution verringert den Anteil der Titanit-Komponentesensu stricto, CaTiSiO,O, auf weniger als 50 Mol% in vielen Analysen. Die Extremzusammensetzung entspricht Ca_0.994Na_0.11) (T_10.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). Das AusmaB dieser Substitution ist unzureichend, um eine neue Mineralspecies zu definieren.

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Zirconolite,allanite and hoegbomite in a marble skarn from the Bergell contact aureole: implications for mobility of Ti,Zr and REE   总被引：1，自引：0，他引：1  

Reto Gieré 《Contributions to Mineralogy and Petrology》1986,93(4):459-470

Zirconolite, allanite and hoegbomite are present as accessory phases in a metasomatically altered spinel-calcite-marble from the contact with the Bergell intrusives (Switzerland/Italy). Textural relationships indicate a step-wise alteration of spinel to 1) hoegbomite or corundum + magnetite, 2) margarite and 3) chlorite. Replacement of spinel by hoegbomite can be described by the substitution 1.94(Mg²⁺, Fe²⁺, Zn²⁺, Mn²⁺, Ca²⁺)Ti⁴⁺ +0.12(OH^–) where Al³⁺ and Fe³⁺ are held constant. The average composition of the Bergell hoegbomites is given by the formula Fe _0.97 ²⁺ Mg_0.69Zn_0.04Ti_0.17Al_3.94Fe _0.06 ³⁺ O_7.98(OH)_0.02 and seems to be imposed by the composition of pre-existing spinel. During the first two steps of spinel alteration, calcite was replaced by anorthite+phlogopite, and the rare earth element(REE)-bearing minerals zirconolite, allanite and sphene were formed. Allanites have characteristic chondrite-normalized REE patterns with enrichment in the light REE. The zirconolite patterns show a marked increase in concentration from La to Ce, followed by an almost constant section. Sphene lacks detectable La, and its REE patterns vary from grain to grain. Contemporaneous formation of phlogopite, REE-bearing minerals and hoegbomite during replacement of the spinel-calcite-marble indicates that the metamorphic fluid introduced potassium along with REE and other high valence cations (Ti⁴⁺, Zr⁴⁺, U⁴⁺, Th^4A3804265, Nb^5A3804265, Y^3A3804265) possibly as polynuclear complexes. The abundance of fluorine-bearing phlogopite and fluor-apatite as well as their close association with REE-bearing minerals and hoegbomite suggests F^– and PO ₄ ^3– as likely ligands for complexing of the above mentioned elements.  相似文献   

Distribution of cations at two tetrahedral sites in Ca2MgSi2O7-Ca2Fe3+AlSiO7 series synthetic melilite and its relation to incommensurate structure     

Maki Hamada  Masahide Akasaka 《Physics and Chemistry of Minerals》2013,40(3):259-270

Synthetic melilites on the join Ca₂MgSi₂O₇ (åkermanite: Ak)-Ca₂Fe³⁺AlSiO₇ (ferrialuminium gehlenite: FAGeh) were studied using X-ray powder diffraction and ⁵⁷Fe Mössbauer spectroscopic methods to determine the distribution of Fe³⁺ between two different tetrahedral sites (T1 and T2), and the relationship between ionic substitution and incommensurate (IC) structure. Melilites were synthesized from starting materials with compositions of Ak₁₀₀, Ak₈₀FAGeh₂₀, Ak₇₀FAGeh₃₀ and Ak₅₀FAGeh₅₀ by sintering at 1,170–1,350 °C and 1 atm. The average chemical compositions and end-member components, Ak, FAGeh and Geh (Ca₂Al₂SiO₇), of the synthetic melilites were Ca_2.015Mg_1.023Si_1.981O₇ (Ak₁₀₀), Ca_2.017Mg_0.788Fe _0.187 ³⁺ Al_0.221Si_1.791O₇ (Ak₇₈FAGeh₁₉Geh₃), Ca_1.995Mg_0.695Fe _0.258 ³⁺ Al_0.318Si_1.723O₇ (Ak₆₉FAGeh₂₅Geh₆) and Ca_1.982Mg_0.495Fe _0.449 ³⁺ Al_0.519Si_1.535O₇ (Ak₄₉FAGeh₄₄Geh₇), respectively. Rietveld refinements using X-ray powder diffraction data measured using CuK _α -radiation at room temperature converged successfully with goodness-of-fits of 1.15–1.26. The refined Fe occupancies at the T1 and T2 sites and the Mg and Si contents determined by electron microprobe analysis gave the site populations of [0.788Mg + 0.082Fe³⁺ + 0.130Al]_T1[0.104Fe³⁺ + 0.104Al + 1.792Si]_T2 for Ak₇₈FAGeh₁₉Geh₃, [0.695Mg + 0.127Fe³⁺ + 0.178Al]_T1[0.132Fe³⁺ + 0.144Al + 1.724Si]_T2 for Ak₆₉FAGeh₂₅Geh₆ and [0.495Mg + 0.202Fe³⁺ + 0.303Al]_T1[0.248Fe³⁺ + 0.216Al + 1.536Si]_T2 for Ak₄₉FAGeh₄₄Geh₇ (apfu: atoms per formula unit), respectively. The results indicate that Fe³⁺ is distributed at both the T1 and the T2 sites. The mean T1–O distance decreases with the substitution of Fe³⁺ + Al³⁺ for Mg²⁺ at the T1 site, whereas the mean T2–O distance increases with substitution of Fe³⁺ + Al³⁺ for Si⁴⁺ at the T2 site, causing decrease in the a dimension and increase in the c dimension. However, in spite of the successful Rietveld refinements for the X-ray powder diffraction data measured using CuK _α-radiation at room temperature, each Bragg reflection measured using CuK _α1-radiation at room temperature showed weak shoulders, which were not observed in those measured at 200 °C. The Mössbauer spectra of the melilites measured at room temperature consist of two doublets assigned to Fe³⁺ at the T1 site and two or three doublets to Fe³⁺ at the T2 site, implying the existence of multiple T1 and T2 sites with different site distortions. These facts can be interpreted in terms of the IC structure in all synthetic melilites at room temperature, respectively. The results of Mössbauer analysis indicate that the IC structure in melilite is caused by not only known multiple T1 site, but also multiple T2 site at room temperature.  相似文献   

Synthesis and characterization of Mn-bearing ilvaite CaFe 2−x 2+ MnxFe3+ [Si2O7/O/(OH)]     

B. Ghazi-Bayat  G. Amthauer  E. Hellner 《Mineralogy and Petrology》1989,40(2):101-109

Summary Synthesis of Mn-bearing ilvaites, CaFe _2–x ²⁺ Mn_xFe³⁺ [Si₂O₇/O/(OH)], with 0 x 0.19, have been performed under hydrothermal conditions at 2 and 3 kbars, T = 300 -400°C and at oxygen fugacities defined by the Fe₂O₃/Fe₃O₄ - and the Ni/NiO -buffer. As shown by X-ray diffraction, the substitution of Fe²⁺ by Mn²⁺ decreases the monoclinic angle and causes a phase transition from monoclinic to orthorhombic at x = 0.19. The Fe-distribution has been determined by Mössbauer spectroscopy.

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Synthese und Charakterisierung von Mn-haltigem Ilvait CaFe _2–x ²⁺ Mn_xFe³⁺ [Si₂O₇/O/(OH)]

Zusammenfassung Mn-haltiger Ilvait CaFe _2–x ²⁺ Mn_x Fe³⁺ [Si₂O₇/O/(OH)] wurde unter hydrothermalen Bedingungen bei Drucken von 2 und 3 kbar, Temperaturen zwischen 300 und 400°C und bei Sauerstoff Fugazitäten, die durch Festkörperpuffer (Fe₂O₃/Fe₃O₄ und Ni/NiO) kontrolliert wurden, hergestellt. Röntgenbeugungsuntersuchungen zeigen, daß mit steigendem Mn-Einbau der monokline Winkel kleiner wird, und daß bei x = 0.19 ein Phasenübergang von der monoklinen zur orthorhombischen Struktur erfolgt. Die Fe-Verteilung wurde mit Mössbauer-Spektroskopie bestimmt.

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With 4 Figures  相似文献   

The crystal structure of an aluminum-rich schorl overgrown by boron-rich olenite from Koralpe, Styria, Austria     

A. Ertl  J. M. Hughes 《Mineralogy and Petrology》2002,75(1-2):69-78

Summary The first natural tourmaline (because tourmaline with ^[4]B has also been synthesized, we distinguish here between natural and synthetic tourmaline) that has been unequivocally demonstrated to contain B as a substituent at the T sites was described from Koralpe, Styria, Austria. This colourless B-rich olenite occurs as rims overgrowing schorl (black crystals up to a few cm) that has not yet been structurally characterized. A crystal structure refinement (R = 0.019) of this Al-rich schorl shows that ^[4]B occurs in the overgrown schorl; the optimized occupants of the atomic positions yield ^X (Na_0.64Ca_0.10K_0.06□_0.20) ^Y (Fe²⁺ _1.72Al_1.08Ti_0.11Zn_0.03□_0.06) ^Z (Al_5.70Mg_0.20Fe_0.08 ²⁺Mn_0.02) (^[3]BO₃)_3.00 ^T (Si_5.76 ^[4]B_0.24)O₁₈ [F_0.11(OH)_3.31O_0.58]. This is the first known (Al-rich) schorl where a structure refinement has detected ^[4]B. Comparing the structure refinements and the chemical composition of the Koralpe schorl and other ^[4]B-bearing tourmalines with tourmalines which contain no ^[4]B, it is of interest that only structure refinements of tourmalines which are low in magnesium and with a higher component of olenite show substantial amounts of ^[4]B; the role of Mg in controlling the amount of ^[4]B is not known, but it seems that an Al-component on the Y site (olenite-component), a boron-enriched environment and special P-T-t conditions are necessary to get tourmaline with substantial amounts of ^[4]B. Received July 7, 2000; revised version accepted June 6, 2001  相似文献   

A Mössbauer and FTIR study of synthetic amphiboles along the magnesioriebeckite – ferri-clinoholmquistite join     

Giancarlo Della Ventura  Günther J. Redhammer  Gianluca Iezzi  Frank C. Hawthorne  Arnaud Papin  Jean-Louis Robert 《Physics and Chemistry of Minerals》2005,32(2):103-113

A series of amphiboles along the magnesioriebeckite—Na₂Mg₃Fe³⁺ ₂Si₈O₂₂(OH)₂– ferri-clinoholmquistite—Li₂Mg₃Fe³⁺ ₂Si₈O₂₂(OH)2 - join, defined by the ^BLi^B Na_–1 exchange vector, were hydrothermally synthesized at 700°C, 0.4 GPa, NNO + 1 redox conditions. Powder XRD and SEM-EDAX showed a very high (> 90%) amphibole yield for all samples. X-ray patterns were indexed in the C2/m space group; refined cell-parameters show a linear decrease of a and as a function of chemistry. IR spectra in the OH-stretching region show four main and rather sharp bands; these are assigned to Mg and Fe²⁺ at M(1,3), and indicate that the obtained amphiboles depart from the nominal octahedral composition (^M1,3Mg₃). The IR spectra also show that there is an increasing filling-up of the A-site for increasing Na in the system (increasing solid-solution toward, arfvedsonite). Mössbauer spectra show four well-defined quadrupole doublets which are assigned to Fe³⁺ at M2 and to Fe²⁺ at M1, M3 and M4, respectively. The Fe³⁺/Fe²⁺ content derived from fitted peak areas show variable Fe³⁺ concentration along the series. Mössbauer spectra also show a distinct alteration of ⁵⁷Fe hyperfine parameters with changing Na–Li at M4. The most evident variation is observed for the quadrupole splitting of Fe³⁺ at M2, which increases by 50% from ferri-clinoholmquistite to magnesio-riebeckite; this suggest that the M2 octahedron in ferri-clinoholmquistite is much closer to the ideal geometry than the M2 octahedron in magnesio-riebeckite. Mössbauer spectra show also a well-defined increase in the Fe²⁺ quadrupole splitting of the M1 and M3 octahedra, which is attributed to the Na–Li distribution at the B-sites.  相似文献   

Synthetic dumortierite: its PTX-dependent compositional variations in the system Al2O3-B2O3-SiO2-H2O     

Günter Werding  Werner Schreyer 《Contributions to Mineralogy and Petrology》1990,105(1):11-24

Dumortierite, generally simplified as Al₇BSi₃O₁₈, was synthesized in the pure system Al₂O₃–B₂O₃–SiO₂–H₂O (ABSH) using gels with variable Al/Si ratios mixed with H₃BO₃ and H₂O in known proportions as starting materials. Synthesis conditions ranged from 3 to 5 and 15 to 20 kbar fluid pressure at 650° to 880°C. On the basis of analyses, synthetic dumortierite shows relatively narrow homogeneity ranges with regard to Al/Si which, however, vary as a function of pressure: at low pressures (3–5 kbar) Al/Si is 2.77–2.94 versus 2.33–2.55 at high pressures (15–20 kbar). Outside of these homogeneity limits, dumortierite was found to coexist with quartz or corundum, depending on the starting composition. Whereas synthetic dumortierite invaribly contains 1.0 boron atom per formula unit (p.f.u.) based on 18 oxygens, the water contents vary drastically as a function of pressure and temperature (1.32–2.30 wt.% H₂O or 0.85–1.47 H p.f.u.). H₂O is an essential component in dumortierite. Structural formulae based on complete chemical analyses of the dumortierites synthesized reveal that there is invariably an Si-deficiency against the ideal number of 3.0 p.f.u. In the calculation procedure used here, this deficiency is balanced by assuming tetrahedral Al. The remaining Al, taken to occupy the octahedral sites, is always below the ideal number of 7.0 p.f.u. Charge-balancing the structure with the hydrogen found analytically leads to two different mechanisms of H incorporation: (1) 3H⁺ + octahedral vacancy for Al^[6]; (2) H⁺ + tetrahedral Al for Si^[4]. Dumortierite synthesized at high fluid pressure contains little Al^[4] and, thus, little H⁺ of type 2; its hydrogen is predominantly present as type 1. Conversely, dumortierite formed at low fluid pressures is high in Al^[4] and hydrogen type 2. The amounts of hydrogen type 1 in low-pressure dumortierites decrease with rising temperatures of synthesis. Typical structural formulae are: (Al_6.670.33)[Al_0.49Si_2.51–O_13.53(OH)_1.47](BO₃) for a low-pressure product, and (Al_6.680.32)[Al_0.09Si_2.91O_13.94(OH)_1.06](BO₃) for a high-pressure product. Independently of the synthesis conditions, dumortierite was found always to be orthorhombic, with b₀/a₀ deviating slightly, but significantly from the valid for hexagonal lattice geometry. As a function of increasing Al/Si in the synthetic crystals, their a₀, c₀, and V₀ rise, whereas b₀ decreases. Thus b₀/a₀ decreases most sensitively with rising Al/Si and also with growing Al^[4]. More experimentation is required before the compositional variations of dumortierite found here can be applied successfully to geothermobarometry of natural rocks.  相似文献   

Cation distribution in amphiboles synthesized along the Ga analogue of the tremolite–aluminotschermakite join     

D. M. Jenkins  K. Ishida  V. Liogys  D. Ghosh 《Physics and Chemistry of Minerals》2002,29(2):87-97

 Amphiboles were synthesized from bulk compositions prepared along the join Ca_1.8Mg_5.2Si₈O₂₂(OH)₂–Ca_1.8Mg₃Ga₄Si₆O₂₂(OH)₂ hydrothermally at 750–850 °C and 1.0–1.8 GPa, and along the join Ca₂Mg₅Si₈O₂₂F₂–Ca₂Mg₃Ga₄Si₆O₂₂F₂, anhydrously at 1000 °C and 0.7 GPa to document how closely the tschermak-type substitution is obeyed in these analogues of aluminous amphiboles. Electron-microprobe analyses and Rietveld X-ray diffraction structure refinements were performed to determine cation site occupancies. The extent of Ga substitution was found to be limited in both joins, but with the fluorine series having about twice the Ga content (0.6 atoms per formula unit, apfu) of the hydroxyl-series amphiboles (0.3 apfu). The tschermak-type substitution was followed very closely in the hydroxyl series with essentially equal partitioning of Ga between tetrahedral and octahedral sites. The fluorine-series amphiboles deviated significantly from the tschermak-type substitution and, instead, appeared to follow a substitution that is close to a Ca-pargasite substitution of the type: ^[6]Ga³⁺+2^[4]Ga³⁺+1/2^[A] Ca²⁺ = ^[6]Mg²⁺+2^[4]Si⁴⁺+1/2^[A]□. Infrared spectroscopy revealed an inverse correlation between the intensity of the OH-stretching bands and the Ga content for the hydroxyl- and fluorine-series amphiboles. The direct correlation between the Ga and F content and inverse relationship between the Ga and OH content may be a general phenomenon present in other minerals and suggests, for example, that high F contents in titanite are controlled by the Al content of the host rock and that there may be similar direct Al–F correlations in tschermakitic amphiboles. Evidence for the possibility that Al (Ga) might substitute onto only a subset of the tetrahedral sites in tschermakitic amphiboles was sought but not observed in this study. Received: 5 March 2001 / Accepted: 31 July 2001  相似文献   

Groundwater quality and its suitability for drinking and agricultural use in Chithar River Basin, Tamil Nadu, India   总被引：8，自引：0，他引：8  

T. Subramani  L. Elango  S. R. Damodarasamy 《Environmental Geology》2005,47(8):1099-1110

Hydrochemistry of groundwater in Chithar Basin, Tamil Nadu, India was used to assess the quality of groundwater for determining its suitability for drinking and agricultural purposes. Physical and chemical parameters of groundwater such as electrical conductivity, pH, total dissolved solids (TDS), Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl^–, HCO₃^–, CO₃^2–, SO₄^2–, NO^–₃, F^–, B^– and SiO₂ were determined. Concentrations of the chemical constituents in groundwater vary spatially and temporarily. Interpretation of analytical data shows that mixed Ca–Mg–Cl, Ca–Cl and Na–Cl are the dominant hydrochemical facies in the study area. Alkali earths (Ca²⁺, Mg²⁺) and strong acids (Cl^–, SO₄^2–) are slightly dominating over alkalis (Na⁺, K⁺) and weak acids (HCO₃^–, CO₃^2–). The abundance of the major ions is as follows: Na⁺ Ca²⁺ Mg²⁺ > K⁺ = Cl^– > HCO₃^–> SO₄^2– > NO₃^– > CO₃^2– . Groundwater in the area is generally hard, fresh to brackish, high to very high saline and low alkaline in nature. High total hardness and TDS in a few places identify the unsuitability of groundwater for drinking and irrigation. Such areas require special care to provide adequate drainage and introduce alternative salt tolerance cropping. Fluoride and boron are within the permissible limits for human consumption and crops as per the international standards.  相似文献   

Titanian andradite in a metapyroxenite layer from the Malenco ultramafics (Italy): implications for Ti-mobility and low oxygen fugacity     

Othmar Müntener  Jörg Hermann 《Contributions to Mineralogy and Petrology》1994,116(1-2):156-168

Ti-andradite (melanite) has been found in a metapyroxenite layer in the upper part of the Malenco ultramafics(Italy), coexisting with clinochlore, diopside and magnetite. Field observations, as well as major and trace elementbulk-rock composition, strongly suggest a cumulate origin for the layer. Textural relationships indicate thatTi-andradite formed during two different metamorphic stages. Under peak metamorphic conditions (400–450°C, 5±2 kbar)Ti-andradite grew in an assemblage of diopside, clinochlore, magnetite and rare ilmenite and perovskite. Later, retrograde brittle deformationinduced formation of veins containing the paragenesis Ti-andradite, vesuvianite, diopside, chlinochlore, magnetite and accessory perovskite.The Ti-andradite varies considerably in TiO₂ (0.11–9.62 wt%), Fe₂O₃(14.3–30.5 wt%), Al₂O₃ (0.65–3.90 wt%), Cr₂O₃(>0.18–0.98 wt%) and SiO₂ (32.1–36.1 wt%); this is mostly, but not entirely, due to distinct zoning.Ti-andradite contains 0.32 to 0.66 wt% H₂O as determined by infrared spectroscopy and 0.83 to 1.76 wt% FeO. The CaO shows almost no variation (34.1±0.7 wt%) and Ca completely fills the dodecahedral site. Single crystal site refinements indicate that no tetrahedral Ti or Fe replaces Si. Titanium incorporation is attributed to similar degrees of substitution along the exchange vectors Ti³⁺ Fe³⁺, Ti⁴⁺ Al^IV Al _-1 ^VI Si_-1 and (Fe²⁺, Mn²⁺, Mg²⁺)Ti⁴⁺ 2Fe _-1 ³⁺ . The presence of mixed valence states of both Fe and Ti suggests a low oxygen fugacity during crystallization of Ti-andradite. Mass balance calculations indicate an isochemical origin of the first generation of Ti-andradite in the clinopyroxenite layer. Its occurrence is restricted to antigorite-free mineral assemblages containing clinochlore of 0.95X _Al>1.1. The hydrothermal crystallization of Ti-rich andradite in veins demonstrates Ti mobility in aqueous fluids under moderate P-T conditions. The zonation patterns indicate disequilibrium conditions during vein crystallization. As no fluorine-, carbonate- and phosphate-bearing minerals were found, OH^- is most probably the ligand complexing Ti.  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   

Structural changes and valence states in the MgCr<Subscript>2</Subscript>O<Subscript>4</Subscript>–FeCr<Subscript>2</Subscript>O<Subscript>4</Subscript> solid solution series     

D.?LenazEmail author  H.?Skogby  F.?Princivalle  U.?H?lenius 《Physics and Chemistry of Minerals》2004,31(9):633-642

The influence on the structure of Fe²⁺ Mg substitution was studied in synthetic single crystals belonging to the MgCr₂O₄–FeCr₂O₄ series produced by flux growth at 900–1200 °C in controlled atmosphere. Samples were analyzed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption-, infrared- and Mössbauer spectroscopy. The Mössbauer data show that iron occurs almost exclusively as ^IVFe²⁺. Only minor Fe³⁺ (<0.005 apfu) was observed in samples with very low total Fe. Optical absorption spectra show that chromium with few exceptions is present as a trivalent cation at the octahedral site. Additional absorption bands attributable to Cr²⁺ and Cr³⁺ at the tetrahedral site are evident in spectra of end-member magnesiochromite and solid-solution crystals with low ferrous contents. Structural parameters a₀, u and T–O increase with chromite content, while the M–O bond distance remains nearly constant, with an average value equal to 1.995(1) Å corresponding to the Cr³⁺ octahedral bond distance. The ideal trend between cell parameter, T–O bond length and Fe²⁺ content (apfu) is described by the following linear relations: a₀=8.3325(5) + 0.0443(8)Fe²⁺ (Å) and T–O=1.9645(6) + 0.033(1)Fe²⁺ (Å) Consequently, Fe²⁺ and Mg tetrahedral bond lengths are equal to 1.998(1) Å and 1.965(1) Å, respectively.  相似文献   

A thermodynamic model of Fe–Cr spinels     

Viktor?A.?KurepinEmail author 《Contributions to Mineralogy and Petrology》2005,149(5):591-599

A new thermodynamic model for multi-component spinel solid solutions has been developed which takes into account thermodynamic consequences of cation mixing in spinel sublattices. It has been applied to the evaluation of thermodynamic functions of cation mixing and thermodynamic properties of Fe₃O₄–FeCr₂O₄ spinels using intracrystalline cation distribution in magnetite, lattice parameters and activity-composition relations of magnetite–chromite solid solutions. According to the model, cation distribution in binary spinels, (Fe_1-x²⁺ Fe_x³⁺)[Fe_x²⁺Fe_2-2y-x³⁺Cr_2y]O₄, and their thermodynamic properties depend strongly on Fe²⁺–Cr³⁺ cation mixing. Mixing of Fe²⁺–Fe³⁺ and Fe³⁺–Cr³⁺ can be accepted as ideal. If Fe²⁺, Fe³⁺ and Cr are denoted as 1, 3 and 4 respectively, the equation of cation distribution is –RT ln(x²/((1–x)(2–2y–x)))= G₁₃^* + (1–2x)W₁₃+y(W₁₄–W₁₃–W₃₄) where G₁₃^* is the difference between the Gibbs energy of inverse and normal magnetite, W_ij is a Margules parameter of cation mixing and G₁₃^*, J/mol =–23,000+13.4 T, W₁₄=36 kJ/mol, W₁₃=W₃₄=0. The positive nonconfigurational Gibbs energy of mixing is the main reason for changing activity–composition relations with temperature. According to the model, the solvus in Fe₃O₄–FeCr₂O₄ spinel has a critical temperature close to 500°C, which is consistent with mineralogical data.  相似文献   

The structure type of Joaquinite     

Dr. E. Cannillo  Dr. F. Mazzi  Dr. G. Rossi 《Mineralogy and Petrology》1972,17(4):233-246

Summary The structure type of joaquinite has been derived from precession photographs (Mo radiation) of a polysynthetic twin. Space group: C 2/m; lattice constants:a=10.50Å,b=9.58Å;c=11.78Å;=109°32;cell content: Ba₄Fe₂RE₄Ti₄O₄[Si₄O₁₂]₄.The atomic arrangement was determined by Patterson-, Fourier-, and (F₀–F_c)-syntheses. The least squares refinement (with isotropic temperature factors) led toR=0.16. The authors are of the opinion that this relativeley highR-value is due to the poor quality of the crystal.The main structural feature are double layers of [Si₄O₁₂]-rings parallel to (001) which are connected by 10-coordinated Ba and octahedrally coordinated Ti. These double layers have pseudo-symmetry C mmm, with mirror planes perpendicular toa, b, andc ^*. They are stacked alongc ^* and translated –3/8a. The orthorhombic pseudo-symmetry allows also the translation +3/8a which is responsible for both the formation of twins and the frequent stacking disorder. The described double layers are connected by 7-coordinated RE and 4-coordinated Fe.The rôles of Fe, which has an occupancy of only 1/2, and of Na and OH. which are reported in published analyses, are discussed.

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Der Strukturtyp von Joaquinit

Zusammenfassung Der Strukturtyp von Joaquinit wurde aus Präzessionsaufnahmen (MoStrlg.) eines polysynthetischen Zwillings abgeleitet. Raumgruppe: C 2/m; Gitterkonstanten:a=10,50Å;b=9,58Å,c=11,78Å; =109°32, Zellinhalt: Ba₄Fe₂SE₄Ti₄O₄[Si₄O₁₂]₄.Die Atomanordnung wurde aus Patterson-, Fourier- und (F₀–F_c)-Synthesen abgeleitet. Die Verfeinerung mit der Methode der Kleinsten Quadrate führte (mit isotropen Temperaturfaktoren) aufR=0,16. Die Autoren sind der Ansicht, daß dieser relativ hoheR-Wert von der schlechten Qualität des Kristalles herrührt.Wesentliches Strukturmotiv sind Doppelschichten von [Si₄O₁₂]-Ringen parallel (001), die durch 10-koordiniertes Ba und oktaedrisch koordiniertes Ti verknüpft werden. Diese Doppelschichten haben die Pseudosymmetrie C mmm mit Symmetrieebenen senkrechta, b undc ^*. Sie werden nachc ^* gestapelt und um –3/8a translatiert. Die rhombische Pseudosymmetrie läßt andererseits die Translation +3a zu, was für die Zwilligsbildung und die häufige Stapelungsunordnung verantwortlich ist. Diese Doppelschichten werden weiter durch 7-koordinierte SE und 4-koordinertes Fe verknüpft.Die Rollen des Fe, welches eine Punktlage nur zur Hälfte besetzt, und des Na und OH, welche in publizierten Analysen angegeben werden, werden diskutiert.

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Mit 10 Abbildungen  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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REE-bearing minerals in a Ti-rich vein from the Adamello contact aureole (Italy)     

Reto Gieré  C. Terry Williams 《Contributions to Mineralogy and Petrology》1992,112(1):83-100

Zirconolite, aeschynite-(Ce), titanite and apatite have been found as minor or accessory minerals in a Ti-rich (TiO₂=2.1–4.5 wt.%) hydrothermal vein occurring in dolomite marbles at the contact with a tonalite intrusion of the Tertiary Adamello batholith (northern Italy). The vein consists of four distinct mineral zones, comprising from margin to center: (1) forsterite+calcite, (2) pargasite+calcite+titanite+sulfides, (3) phlogopite +calcite+titanite+sulfides, and (4) titanian clinohumite +spinel+calcite+sulfides. Zirconolite occurs in two vein zones only: in the phlogopite zone it is invariably anhedral, often corroded, and exhibits complex chemical zonation patterns. In the titanian clinohumite zone zirconolite is idiomorphic and characterized by a pronounced discontinous chemical zoning, but shows no evidence of corrosion. The considerable compositional variation observed for zirconolite (in wt.%: (REE₂O₃)=0.74–16.8, UO₂=0.59–24.0, ThO₂=0.67–17.1) is due to the zoning, and may be attributed to four major substitutions described by the exchange vectors:

1.	(Th, U) (Mg, Fe2+) Ca-1 Ti-1
2.	REE Al Ca-1 Ti-1
3.	REE Fe2+ (Nb, Ta) Ca-1 Ti-1
4.	Hf Zr-1

Exchange vector (2) is effective at total REE₂O₃ contents up to approximately 5 wt.%, whereas vector (3) is operating at higher concentrations. Both titanite and aeschynite-(Ce) exhibit, like zirconolite, complex chemical zonation patterns which document that the trace element content of the metasomatic fluid was variable during the vein-forming process. As indicated by thermodynamic analysis of the phase assemblages, the vein zones containing the REE-bearing minerals formed at 500–600°C (P_total2 kbar) from a reducing fluid rich in H₂S, HCl°, HF° and phosphorus, but relatively poor in CO₂(X_{CO 2} 0.2). Geochemical and isotopic data are consistent with the interpretation of the fluid as being derived from the nearby tonalite intrusion. The abundance of idiomorphic fluor-apatite as well as textural relations between apatite, the other REE-bearing minerals and the fluorine-bearing hydrous silicates suggest F^- and PO ₄ ^3- to be the most likely ligands for complexing REE, Ti, Zr and other high-field-strength elements in the veinforming fluid. The corrosive features observed for zirconolite demonstrate that hydrothermal fluids are able to dissolve zirconolite, which is one of the main components of SYNROC-C, the most promising disposal option for high-level nuclear waste. Therefore, immobilization of radioactive waste in zirconolite can be guaranteed only if an effective sealing material prevents any hydrothermal fluid from access to the final disposal site.  相似文献   

Anomalous optical variations in the grossular garnet from the Eden Mills,Belvidere Mountain (Vermont,USA)     

Manzoor Ahmad Badar  Safdar Hussain  Shanawer Niaz  Saif ur Rehman 《Arabian Journal of Geosciences》2016,9(9):545

The optical anomalies, and surface and lamellar textures of a birefringent grossular garnet crystal from the Eden Mills, Belvidere Mountain, Vermont, USA, have been investigated by optical polarizing microscope, electron-probe micro-analyzer, back-scattered electron imaging, infrared spectroscopy, and single-crystal X-ray diffractometer from the standpoint of crystal growth. This grossular shows one-to-one correlation between natural surface features and its internal textures under crossed polarizers. Electron-probe micro-analyzer (EPMA) gave average chemical composition in (110) thin section, of bright lamella {Ca_2.97Mn_0.06}_∑3.03 [Al_1.59Fe_0.37Ti_0.01]_∑1.97(Si_3.00)_∑3.00 (Gros_79.5And_18.9Sps_1.6) and of dark host {Ca_2.99Mn _0.06}_∑3.05 [Al_1.73Fe_0.26 Ti_0.01]_∑2.00(Si_2.97OH_0.03)_∑3.00 (Gros_85.4And₁₃Sps_1.6). The correspondence of surface features and the internal textures with spiral or pyramidal growth mechanism suggest that the internal textures of the Eden Mills grossular are formed during growth process. The optical vibrational orientations and the growth steps inclination along [001] and \( \left[\overset{-}{1}10\right] \) directions predict monoclinic symmetry. With X-ray diffractometer (XRD) method, pseudocubic parameters are a = 11.839(2) Å, b = 11.855(1) Å, and c = 11.868(2) Å with interaxial angles α = 90.00(1)°, β = 89.99(1)°, and γ = 90.02(2)° that show orthorhombic symmetry of this crystal. Lamellar texture of Al³⁺-rich host with Fe³⁺-rich lamella infers cation ordering at octahedral site of the garnet structure. IR data favors the non-cubic orientation of [(OH) ₄] at tetrahedral position in this grossular structure.  相似文献