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1.
The crystal structures of synthetic K-dravite [XKYMg 3 Z Al 6 T Si6O18(BO3) 3 V (OH) 3 W (OH)], dravite [XNaYMg 3 Z Al 6 T Si6O18(BO3) 3 V (OH) 3 W (OH)], oxy-uvite [XCaYMg 3 Z Al 6 T Si6O18(BO3) 3 V (OH) 3 W O], and magnesio-foitite [X?Y(Mg2Al)ZAl 6 T Si6O18(BO3) 3 V (OH) 3 W (OH)] are investigated by polarized Raman spectroscopy, single-crystal structure refinement (SREF), and powder X-ray diffraction. The use of compositionally simple tourmalines characterized by electron microprobe analysis facilitates the determination of site occupancy in the SREF and band assignment in the Raman spectra. The synthesized K-dravite, oxy-uvite, and magnesio-foitite have significant Mg–Al disorder between their octahedral sites indicated by their respective average 〈Y–O〉 and 〈Z–O〉 bond lengths. The Y- and Z-site compositions of oxy-uvite (YMg1.52Al1.48(10) and ZAl4.90Mg1.10(15)) and magnesio-foitite (YAl1.62Mg1.38(18) and ZAl4.92Mg1.08(24)) are refined from the electron densities at each site. The Mg–Al ratio of the Y and Z sites is also determined from the relative integrated peak intensities of the Raman bands in the O–H stretching vibrational range (3250–3850 cm?1), producing values in good agreement with the SREF data. The unit cell volume of tourmaline increases from magnesio-foitite (1558.4(3) Å3) to dravite (1569.5(4)–1571.7(3) Å3) to oxy-uvite (1572.4(2) Å3) to K-dravite (1588.1(2) Å3), mainly due to lengthening of the crystallographic c-axis. The increase in the size of the X-site coordination polyhedron from dravite (Na) to K-dravite (K) is accommodated locally in the crystal structure, resulting in the shortening of the neighboring O1–H1 bond. In oxy-uvite, Ca2+ is locally associated with a deprotonated W (O1) site, whereas vacant X sites are neighbored by protonated W (O1) sites. Increasing the size of the X-site-occupying ion does not detectably affect bonding between the other sites; however, the higher charge of Ca and the deprotonated W (O1) site in oxy-uvite are correlated to changes in the lattice vibration Raman spectrum (100–1200 cm?1), particularly for bands assigned to the T 6O18 ring. The Raman spectrum of magnesio-foitite shows significant deviations from those of K-dravite, dravite, and oxy-uvite in both the lattice and O–H stretching vibrational ranges (100–1200 and 3250–3850 cm?1, respectively). The vacant X site is correlated with long- and short-range changes in the crystal structure, i.e., deformation of the T 6O18 ring and lengthening of the O1–H1 and O3–H3 bonds. However, X-site vacancies in K-dravite, dravite, and oxy-uvite result only in the lengthening of the neighboring O1–H1 bond and do not result in identifiable changes in the lattice-bonding environment.  相似文献   

2.
Polarized Fourier-transform infrared and Raman spectra were acquired on an elbaite sample previously characterized by electron- and ion microprobe analysis, X-ray diffraction and structure refinement. Spectra from the two vibrational spectroscopy techniques reveal a close similarity in the OH-stretching region, with three main absorption bands strongly polarized in the c-axis direction. By means of bond-valence theory arguments, the observed OH bands are interpreted and assigned to specific local cation arrangements around the O1 (≡W) and O3 (≡V) anion sites. In combination with the relatively simple composition of the studied sample, bond-valence constraints are used to identify stable anion-cation arrangements, which permit the occurrence of short-range ordering to be assessed. Evidence for nearly complete short-range order at the O1 site, with the stable arrangements Y(LiAlAl)0.6–W(OH)0.6 and Y(LiLiAl)0.4–W(F)0.4, are presented. These two local arrangements can be further expanded to obtain the larger ordered clusters [W(OH)–Y(LiAl2)–V(OH)3–Z(Al)6]0.6 and [W(F)–Y(Li2Al)–V(OH)3–Z(Al)6]0.4.  相似文献   

3.
Pale-blue to pale-green tourmalines from the contact zone of Permian pegmatites to mica schists and marbles from different localities of the Austroalpine basement units (Rappold Complex) in Styria, Austria, are characterized. All these Mg-rich tourmalines have small but significant Li contents, up to 0.29 wt% Li2O, and can be characterized as dravite, with FeO contents of ?~?0.9–2.7 wt%. Their chemical composition varies from X (Na0.67Ca0.19?K0.02?0.12) Y (Mg1.26Al0.97Fe2+ 0.36Li0.19Ti4+ 0.06Zn0.01?0.15) Z (Al5.31?Mg0.69) (BO3)3 Si6O18 V (OH)3? W [F0.66(OH)0.34], with a?=?15.9220(3), c?=?7.1732(2) Å to X (Na0.67Ca0.24?K0.02?0.07) Y (Mg1.83Al0.88Fe2+ 0.20Li0.08Zn0.01Ti4+ 0.01?0.09) Z (Al5.25?Mg0.75) (BO3)3 Si6O18 V (OH)3? W [F0.87(OH)0.13], with a?=?15.9354(4), c?=?7.1934(4) Å, and they show a significant Al-Mg disorder between the Y and the Z sites (R1?=?0.013–0.015). There is a positive correlation between the Ca content and?<?Y-O?>?distance for all investigated tourmalines (r?≈?1.00), which may reflect short-range order configurations including Ca and Fe2+, Mg, and Li. The tourmalines have XMg (XMg?=?Mg/Mg?+?Fetotal) values in the range 0.84–0.95. The REE patterns show more or less pronounced negative Eu and positive Yb anomalies. In comparison to tourmalines from highly-evolved pegmatites, the tourmaline samples from the border zone of the pegmatites of the Rappold Complex contain relatively low amounts of total REE (~8–36 ppm) and Th (0.1–1.8 ppm) and have low LaN/YbN ratios. There is a positive correlation (r?≈?0.91) between MgO of the tourmalines and the MgO contents of the surrounding mica schists. We conclude that the pegmatites formed by anatectic melting of mica schists and paragneisses in Permian time. The tourmalines crystallized from the pegmatitic melt, influenced by the metacarbonate and metapelitic host rocks.  相似文献   

4.
Heat treatment was performed on selected Fe-dominant tourmalines to establish the nature of any change in optical properties. Two tourmaline samples from Dolní Bory, Czech Republic (TDB) and Vlachovo, Slovakia (TVL) were heated at 450, 700 and 900°C at 0.1 mPa and ambient oxidation conditions for 8 h. EMPA study shows that tourmaline from Vlachovo has schorlitic composition and tourmaline from Dolní Bory is alkali-depleted schorl to foitite. Although the black colour remained unchanged after heating at 450°C, it changed to brown at 700°C and reddish brown at 900°C. No significant changes of chemical composition were observed during heating. X-ray diffraction, infrared and Mössbauer study showed negligible oxidation of tourmaline heated at 450°C, but a significant change in iron valency state and deprotonization at 700°C. The oxidation of Fe is the main cause of tourmaline colour change, and the substitution vector for oxidation of Fe is Fe3+OFe ?1 2+ (OH)?1. The predicted deprotonization of OH was confirmed by infrared spectroscopy, which documented a decrease in OH groups in both samples, mainly at the V site. The oxidation of Fe is mostly significant in the Y site as documented on the compression of the Y-site octahedra and subsequent decrease in the a lattice parameter. This feature is consistent with lattice dimensions in the transition from schorl and foitite dimensions to those consistent with fluor-buergerite. The Z-site octahedra did not compressed and were not affected by heating-induced Fe oxidation, which indicates only negligible content of Z Fe2+ in original samples. After heating at 900°C, the tourmaline structure collapsed likely due to the thermally induced weakening of bonds in Y and Z octahedra, which results in amorphization of tourmaline. Subsequently, breakdown products including Fe-oxides and mullite replaced alkali-depleted amorphized tourmaline.  相似文献   

5.
Abstract Three reactions are calibrated as geothermobarometers for garnet–orthopyroxene–plagioclase–quartz assemblages, namely: 1/2 ferrosilite + 1/3 pyrope ± 1/2 enstatite + 1/3 almandine (A): ferrosilite + anorthite ± 2/3 almandine + 1/3 grossularite + quartz (B); and enstatite + anorthite ± 2/3 pyrope + 1/3 grossularite + quartz (C). The internally consistent geothermobarometers based on reactions (A), (B) and (C) are calibrated from experimental data only. The thermodynamic parameters of reaction (A) are derived from published experimental data in the FMAS system (n= 104) in the range 700–1400°C and 5–50 kbar, while those for reaction (B) are derived by summation of the existing reversed experimental data of the mineral equilibria: ferrosilite ± fayalite + quartz (D) and anorthite + fayalite ± 2/3 almandine + 1/3 grossularite (E). The retrieved thermodynamic parameters for reactions (A), (B) and (C) are, respectively: (ΔH0, cal) -3367 ± 209, -2749 ± 350 and +3985 ± 545; (ΔS0, cal K?1) -1.634 ± 0.163, -8.644 ± 0.298 and -5.376 ± 0.391; and (ΔV01,298, cal bar?1) -0.024, -0.60946 and -0.5614. On a one-cation basis, the derived Margules parameters of the ternary Ca–Fe–Mg in garnet are: WFe–Mg= -1256 + 1.0 (～0.23) T(K), WMg–Fe= 2880 -1.7 (～0.13) T(K), WCa–Mg= 4047 (～77) -1.5 T(K), WMg–Ca= 1000 (～77) -1.5 T(K), WCa–Fe= -723 + 0.332 (～0.02) T(K), WFe–Ca= 1090, (cal) and the ternary constant C123= -4498 + 1.516 (～0.265) T(K) cal (subregular solution model of non-ideal mixing); and Fe–Mg–Al in orthopyroxene: WFe–Mg= 948 (～200) -0.34 (～0.10) T(K), WFe–Al= -1950 (～500) and WMg–Al= 0 (cal) (regular solution model of non-ideal mixing). The anorthite activity in plagioclase is calculated by the ‘Al-avoidance’model of subregular Ca–Na mixing commonly used for geobarometry based on reactions (B) and (C). When the geothermobarometers are applied to garnet–orthopyroxene–plagioclase–quartz assemblages (n= 45) of wide compositional range from the Precambrian South Indian granulites, temperature ranges of 690–860°C (X= 760 ± 45°C) and pressure ranges of 5–10 kbar were obtained. The P–T values were estimated simultaneously and there is no difference in the pressure calculated from PMg (reaction C) and PFe (reaction B). In the existing calibrations this difference is 1 kbar or more. Furthermore, there is no compositional dependence of the ln K of the experimental data in the FMAS (n= 104) and the CFMAS (n= 78) systems at different temperatures and the estimated temperatures of the South Indian granulites.  相似文献   

6.
The crystal structure of the rare secondary mineral cualstibite-1M (formerly cyanophyllite), originally reported to have the chemical formula 10CuO·2Al2O3·3Sb2O3·25H2O and orthorhombic symmetry, was solved from single-crystal intensity data (Mo-Kα X-radiation, CCD area detector, 293 K, 2θmax?=?80) collected on a twinned crystal containing very minor Mg. The mineral is monoclinic, P21/c (no. 14), with a?=?9.938(1), b?=?8.890(1), c?=?5.493(1) Å, β?=?102.90(1)°, V?=?473.05(11) Å3; R1(F)?=?0.0326. All crystals investigated turned out to be non-merohedric twins. The atomic arrangement has a distinctly layered character. Brucite-like sheets composed of two [4?+?2]-coordinated (Cu,Al,Mg) sites are linked by weak hydrogen-bonding (O···O?~?2.80 Å) to isolated regular Sb(OH)6 octahedra (<Sb-O>?=?1.975 Å). The layered, pseudotrigonal character explains the perfect cleavage and the proneness to twinning. The Sb site is fully occupied and the two (Cu,Al,Mg) sites have occupancies of Cu0.79Al0.17Mg0.04 and Cu0.72Al0.23Mg0.05. The Cu-richer site shows a slightly stronger Jahn-Teller-distortion. The resulting empirical formula, which necessitates a H2O-for-OH substitution to obtain charge balance, is (Cu2.23Al0.63Mg0.14)(OH)5.63(H2O)0.37[Sb5+(OH)6]. The ideal chemical formula is (Cu,Al)3(OH)6[Sb5+(OH)6], with Cu:Al = 2:1. The structure is closely related to those of trigonal cualstibite-1T [Cu2AlSb(OH)12, P-3, with ordered Cu-Al distribution in the brucite sheets], and its Zn analogue zincalstibite-1T [Zn2AlSb(OH)12]. Cualstibite-1M and cualstibite-1T are polytypes and, together with zincalstibite-1T, zincalstibite-9R and omsite, belong to the cualstibite group within the hydrotalcite supergroup, which comprises all natural members of the large family of layered double hydroxides (LDH).  相似文献   

7.
Health hazards from heavy metal pollution in water systems are a global environmental problem. Of similar concern is sludge that results from wastewater treatment due to unsatisfactory sludge management technology. Therefore, the effectiveness of using Mg–Al-layered double hydroxide in the removal of heavy metals from mine wastewater was tested and compared with that of calcium hydroxide [Ca(OH)2], which is a common treatment method for heavy metal removal. Initially, the mine wastewater contained cations of the heavy metals iron (Fe), zinc (Zn), copper (Cu), and lead (Pb). The Mg–Al-layered double hydroxides were able to remove 371, 7.2, 121, and 0.4 mg/L of these pollutants, respectively, using the co-precipitation method. The removal of these metals is most effective using 0.5 g Mg–Al-layered double hydroxide (Mg/Al molar ratio 4) and 20 min of shaking. Zn was removed by the formation of Zn(NO3)(OH)·H2O and Zn5(NO3)2(OH)8 when LDH, Mg/Al molar ratios of 4 and 2, respectively, were used. Similarly, Fe, Cu, and Pb were removed by the formation of Fe–Al-layered double hydroxide, Cu2(OH)3·NO3 and Pb4(OH)4(NO3)4, respectively. While Ca(OH)2 is also capable of reducing the heavy metal concentrations below the Japanese recommended values, this analysis shows that using 0.5 g Mg–Al-layered double hydroxide is a better treatment condition for mine wastewater, because it generates lower sludge volumes than 0.1 g of Ca(OH)2. The measured sludge volume was 1.5 mL for Mg–Al-layered double hydroxide and 2.5 mL for Ca(OH)2, a nearly twofold further reduction.  相似文献   

8.
Tourmalines from the Kalinovka porphyry copper deposit with epithermal bismuth-gold-basemetal mineralization and the Michurino gold-silver-base-metal prospect have been studied in the South Urals. Tourmaline from the Kalinovka deposit occurs as pockets and veinlets in quartz-sericite metasomatic rock and propylite. The early schorl-“oxy-schorl” [Fetot/(Fetot + Mg) = 0.66?0.81] enriched in Fe3+ is characterized by the homovalent isomorphic substitution of Fe3+ for Al typical of propylites at porphyry copper deposits. The overgrowing tourmalines of the second and third generations from propylite and quartz-sericite metasomatic rock are intermediate members of the dravite-magnesio-foitite solid solution series [Fetot/(Fetot + Mg) = 0.05?0.46] with homovalent substitution of Mg for Fe2+ and coupled substitution of X ? + YAl for XNa + YMg. These substitutions differ from the coupled substitution of YAl + WO2? for YFe2+ + WOH? in tourmaline from quartz-sericite rocks at porphyry copper deposits. At the Michurino prospect, the tourmaline hosted in the chlorite-pyrite-quartz veins and veinlets with Ag-Au-Cu-Pb-Zn mineralization is an intermediate member of the dravite-magnesio-foitite solid solution series [Fetot/(Fetot + Mg) = 0.20?0.31] with homovalent substitution of Mg for Fe2+ and coupled substitutions of X ? + YAl for XNa + YMg identical to that of late tourmaline at the Kalinovka deposit. Thus, tourmalines of the porphyry and epithermal stages are different in isomorphic substitutions, which allow us to consider tourmaline as an indicator of super- or juxtaposed mineralization.  相似文献   

9.
Multiphase solid inclusions in minerals formed at ultra-high-pressure (UHP) provide evidence for the presence of fluids during deep subduction. This study focuses on barian mica, which is a common phase in multiphase solid inclusions enclosed in garnet from mantle-derived UHP garnet peridotites in the Saxothuringian basement of the northern Bohemian Massif. The documented compositional variability and substitution trends provide constraints on crystallization medium of the barian mica and allow making inferences on its source. Barian mica in the multiphase solid inclusions belongs to trioctahedral micas and represents a solid solution of phlogopite KMg3(Si3Al)O10(OH)2, kinoshitalite BaMg3(Al2Si2)O10(OH)2 and ferrokinoshitalite BaFe3(Al2Si2)O10(OH)2. In addition to Ba (0.24–0.67 apfu), mica is significantly enriched in Mg (XMg ~ 0.85 to 0.95), Cr (0.03–0.43 apfu) and Cl (0.04–0.34 apfu). The substitution vector involving Ba in the I-site which describes the observed chemical variability can be expressed as BaFeIVAlClK?1Mg?1Si?1(OH)?1. A minor amount of Cr and VIAl enters octahedral sites following a substitution vector VI(Cr,Al)2□VI(Mg,Fe)?3 towards chromphyllite and muscovite. As demonstrated by variable Ba and Cl contents positively correlating with Fe, barian mica composition is partly controlled by its crystal structure. Textural evidence shows that barian mica, together with other minerals in multiphase solid inclusions, crystallized from fluids trapped during garnet growth. The unusual chemical composition of mica reflects the mixing of two distinct sources: (1) an internal source, i.e. the host peridotite and its garnet, providing Mg, Fe, Al, Cr, and (2) an external source, represented by crustal-derived subduction-zone fluids supplying Ba, K and Cl. At UHP–UHT conditions recorded by the associated diamond-bearing metasediments (c. 1100 °C and 4.5 GPa) located above the second critical point in the pelitic system, the produced subduction-zone fluids transporting the elements into the overlying mantle wedge had a solute-rich composition with properties of a hydrous melt. The occurrence of barian mica with a specific chemistry in barium-poor mantle rocks demonstrates the importance of its thorough chemical characterization.  相似文献   

10.
Babingtonite, Ca2Fe2+Fe3+[Si5O14(OH)] (Z?=?2, space group $ P\overline{1} $ ) from Yakuki mine (Japan), Grönsjöberget (Sweden), Kandivali Quarry (India), Baveno Quarry (Italy), Bråstad Mine (Norway), and Kouragahana (Japan), and manganbabingtonite, Ca2(Mn2+, Fe2+)Fe3+[Si5O14(OH)], from Iron Cap mine (USA) were studied using electron-microprobe analysis (EMPA), 57Fe Mössbauer analysis and single-crystal X-ray diffraction methods to determine the cation distribution at M1 and M2 and to analyze its effect on the crystal structure of babingtonite. Although all studied babingtonite crystals are relatively homogeneous, chemical zonation due to mainly Fe ? Mn substitution is observed in manganbabingtonite. Mössbauer spectra consist of two doublets with isomer shift (I.S.)?=?1.16–1.22 mm/s and quadrupole splitting (Q.S.)?=?2.33–2.50 mm/s and with I.S.?=?0.38–0.42 mm/s and Q.S.?=?0.82–0.90 mm/s, assigned to Fe2+ and Fe3+ at the M1 and M2 octahedral sites, respectively. The determined ratio of Fe2+/total Fe in manganbabingtonite (0.26) was smaller than that in the others (0.35–0.44) because of high Mn2+ content instead of Fe2+. The unit-cell parameters of babingtonite are a?=?7.466–7.478, b?=?11.624–11.642, c?=?6.681–6.690 Å, α?=?91.53–91.59, β?=?93.86–93.94, γ?=?104.20–104.34º, and V?=?560.2–562.3 Å3, and those of manganbabingtonite are a?=?7.4967(3), b?=?11.6632(4), c?=?6.7014(2) Å, α?=?91.602(2), β?=?93.989(2), γ?=?104.574(3)º, and V =565.09(5) Å3. Structural refinements converged to R 1 values of 1.64–3.16 %. The <M1-O> distance was lengthened due to the substitution of large octahedral cations such as Mn2+ for Fe2+. The increase of the M1-O8, M1-O8’ and M1-O13 lengths with mean ionic radii is slightly more pronounced than of the other M1-Oi lengths. The lengthened M1-O13 distance leads the positive correlation between Si5-O15-Si1 angle and M1-O13 distance. The increase of Si2-O3-Si1 and Si5-O12-Si4 angles due to the increase of mean ionic radius of M2 is also observed.  相似文献   

11.
We present structural information obtained on spinel and alumina at high temperature (298-2400 K) using in-situ XANES at the Mg and Al K-edges. For spinel, [4](Alx,Mg1−x)[6](Al2−x,Mgx)O4, with increasing temperature, a substitution of Mg by Al and Al by Mg in their respective sites is observed. This substitution corresponds to an inversion of the Mg and Al sites. There is a significant change in the Al K-edge spectra between crystal and liquid, which can be attributed to a change of the [6]Al normally observed in corundum at room temperature, to a mixture of [6]Al-[4]Al in the liquid state. This conclusion is in good agreement with previous 27Al NMR experiments. Furthermore, both experiments at the Al and Mg K-edges are in good agreement with XANES calculation made using FDMNES code.  相似文献   

12.
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 (Na0.64Ca0.10K0.06□0.20) Y (Fe2+ 1.72Al1.08Ti0.11Zn0.03□0.06) Z (Al5.70Mg0.20Fe0.08 2+Mn0.02) ([3]BO3)3.00 T (Si5.76 [4]B0.24)O18 [F0.11(OH)3.31O0.58]. 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   

13.
Pumpellyite of the general formula W8X4Y8-Z12O56-n(OH)n contains Fe, Al and Mg in two crystallographically different octahedral sites. Three different pumpellyite samples covering the known compositional field from Al- to Fe-rich have been studied to determine the valence state and intracrystalline partitioning of the Fe cations between the two independent octahedral sites. Fe+2 and Fe+3 cation partitioning is interpreted on the basis of results obtained by 57Fe Mössbauer spectroscopy at 293 and 77 K and from Rietveld structure analysis performed on powder X-ray diffraction data. Pumpellyite from low-grade metamorphic rocks typically contains a majority of iron in the Fe+3 oxidation state, which is found in the smaller and less symmetrical octahedral Y-site. Fe+2 was also present in all pumpellyite samples studied and it is located in the larger and more symmetrical octahedral X-site.  相似文献   

14.
Two pumpellyites with the general formula W 8 X 4 Y 8 Z 12O56-n (OH) n were studied using 57Fe Mössbauer spectroscopic and X-ray Rietveld methods to investigate the relationship between the crystal chemical behavior of iron and structural change. The samples are ferrian pumpellyite-(Al) collected from Mitsu and Kouragahana, Shimane Peninsula, Japan. Rietveld refinements gave Fe(X):Fe(Y) ratios (%) of 41.5(4):58.5(4) for the Mitsu pumpellyite and 46(1):54(1) for the Kouragahana pumpellyite, where Fe(X) and Fe(Y) represent Fe content at the X and Y sites, respectively. The Mössbauer spectra consisted of two Fe2+ and two Fe3+ doublets for the Mitsu pumpellyite, and one Fe2+ and two Fe3+ doublets for the Kouragahana pumpellyite. In terms of the area ratios of the Mössbauer doublets and the Fe(X):Fe(Y) ratios determined by the Rietveld refinements, Fe2+(X):Fe3+(X):Fe3+(Y) ratios are determined to be 22:14:64 for the Mitsu pumpellyite and 27:8:65 for the Kouragahana pumpellyite. By applying the Fe2+:Fe3+-ratio determined by the Mössbauer analysis and the site occupancies of Fe at the X and Y sites given by the Rietveld method together with chemical analysis, the resulting formula of the Mitsu and Kouragahana pumpellyites are established as Ca8(Fe 0.88 2+ Mg0.68Fe 0.77 3+ Al1.66)Σ3.99(Al5.67Fe 2.34 3+ )Σ8.01Si12O42.41(OH)13.59 and Ca8(Mg1.24Fe 0.65 2+ Fe 0.46 3+ Al1.66)Σ4.01(Al6.71Fe 1.29 3+ )Σ8.00Si12O42.14(OH)13.86, respectively. Mean Y–O distances and volumes of the YO6 octahedra increase with increasing mean ionic radii, i.e., the Fe3+→Al substitution at the Y site. However, change of the sizes of XO6 octahedra against the mean ionic radii at the X site is not distinct, and tends to depend on the volume change of the YO6 octahedra. Thus, the geometrical change of the YO6 octahedra with Fe3+→Al substitution at the Y site is essential for the structural changes of pumpellyite. The expansion of the YO6 octahedra by the ionic substitution of Fe3+ for Al causes gradual change of the octahedra to more symmetrical and regular forms.  相似文献   

15.
Tourmaline-out isograd formed by the breakdown of tourmaline is defined in the upper amphibolite-facies metapelites in the Yanai area, Ryoke metamorphic belt, SW Japan. The rim composition of tourmaline progressively becomes aluminous with ascending metamorphic grade, and the chemical zoning of tourmaline is controlled by X□AlNa–1Mg–1 and MgTiYAl–2 vectors in low- to medium-grade zones where muscovite is stable, whereas it is controlled by Mg(OH)YAl–1O–1, CaMgOX□–1 YAl–1(OH)–1 and MgTiYAl–2 vectors in further higher–grade, muscovite-unstable zones. The size of tourmaline increases drastically where breakdown of muscovite+quartz takes place, probably due to the growth of tourmaline during breakdown of muscovite. On the high-temperature side of the tourmaline-out isograd, depletion of whole-rock boron is observed. Escape of boron-bearing melt or the fluid evolved from the melt during its crystallization probably caused this depletion, although locally trapped, boron-bearing melt or fluid formed irregularly shaped tourmaline and dumortierite during retrograde metamorphism.  相似文献   

16.
Ferrovalleriite, ideally 2(Fe,Cu)S · 1.5Fe(OH)2, a layered hydroxide-sulfide of the valleriite group and an analog of valleriite with Fe instead of Mg in the hydroxide block, has been approved by the IMA Commission on New Minerals, Nomenclature and Classification as a valid mineral species. It was found in the Oktyabr’sky Mine, Noril’sk, Krasnoyarsk krai, Siberia, Russia. Ferrovalleriite occurs in cavities of massive sulfide ore mainly consisting of cubanite and mooihoekite. In different cases, it is associated with magnetite, Fe-rich chlorite-like phyllosilicate, ferrotochilinite, hibbingite, or rhodochrosite. Ferrovalleriite forms crystals flattened on [001] (from scaly to tabular; up to 5 mm across and up to 0.3 mm thick), typically split and curved. Occasionally, they are combined into aggregates up to 1.5 × 2 cm. Ferrovalleriite is dark bronze-colored, with a metallic luster and black streak. The Mohs’ hardness is ca. 1; VHN is 35 kg/mm2. Cleavage is perfect parallel to {001}, mica-like. Individuals are flexible and inelastic. D(calc) = 3.72 g/cm3. In reflected light, ferrovalleriite is pleochroic from yellowish to gray; bireflectance is moderate. Anisotropy is strong, with bluish gray to yellowish beige rotation colors. Reflectance values [R 1–R 2 %, (λ, nm)] are: 15.6–16.6 (470), 14.8–20.5 (546), 14.7–22.3 (589), 14.5–24.1 (650). The IR spectrum shows the presence of (OH) groups bonded with Fe cations and the absence of H2O molecules. The chemical composition of the holotype (wt %; electron microprobe, H content is calculated) is as follows: 0.10 Al, 0.03 Mn, 45.31 Fe, 0.07 Ni, 18.29 Cu, 20.37 S, 15.62 O, 0.98 H, total is 100.77. The empirical formula calculated on the basis of 2 S atoms is: Al0.01Fe2.55Cu0.91S2(OH)3.07 = (Fe1.09Cu0.91)Σ2S2 · (Fe 1.34 2+ Fe 0.12 3+ Al0.01)Σ1.47(OH)3.07. The structure of ferrovalleriite is incommensurate (misfit); two sublattices are present: (1) sulfide sublattice, space group $R\bar 3m$ , R3m or R32; the unit-cell dimensions are: a = 3.792(2), c = 34.06(3) Å, V = 424(1) Å3 and (2) hydroxide sublattice, space group $P\bar 3m1$ , P3m1 or P321; the unit-cell dimensions: a = 3.202(3), c = 11.35(2)Å, V = 100.8(3) Å3. Together with this main polytype modification with three-layer (R-cell, Z = 3) sulfide block, the holotype ferrovalleriite contains the modification with one-layer (P-cell, Z = 1) sulfide block (sulfide sublattice with $P\bar 3m1$ , P3m1 or P321, unit cell dimensions: a = 3.789(4), c = 11.35(1) Å, V = 141(5) Å3). The strongest reflections in the X-ray powder pattern (d, Å-I) are: 5.69–100; 3.268–58; 3.163–36; 1.894–34; 1.871–45.  相似文献   

17.
《Applied Geochemistry》2001,16(5):559-570
Fe(II)–Fe(III) layered double hydroxysalt green rusts, GRs, are very reactive compounds with the general formula, [FeII(1−x) FeIIIx (OH)2]x+·[(x/n) An−·(m/n) H2O]x−, where x is the ratio FeIII/Fetot, and reflects the structure in which brucite-like layers alternate with interlayers of anions An− and water molecules. Two types of crystal structure for GRs, GR1 and GR2, represented by the hydroxychloride GR1(Cl−) and the hydroxysulphate GR2(SO42−) are distinguished by X-ray diffraction due to different stacking. By analogy with GR1(Cl−) the structure of the fougerite GR mineral, [FeII(1−x) FeIIIx (OH)2]x+·[x OH−·(1−x) H2O]x-  Fe(OH)(2+x)·(1−x) H2O, is proposed displaying interlayers made of OH− ions and water molecules (in situ deprotonation of water molecules is necessary for explaining the flexibility of its composition). The space group of mineral GR1(OH−) would be R3̄m, with lattice parameters a≅0.32 and c≅2.25 nm. Stability conditions and the Eh-pH diagram of Fe(OH)(2+x) (the water molecules are omitted) are determined from hydromorphic soil solution equilibria with GR mineral in Brittany (France). Computed Gibbs free energies of formation from soil solution/mineral equilibrium fit well with a regular solid solution model: μ°[Fe(OH)(2+x)]=(1−x) μ°[Fe(OH)2]+x μ°[Fe(OH)3]+RT [(1−x) ln (1−x)+x ln x]+A0 x (1−x), where μ°[Fe(OH)2]=−492.5 kJ mol−1, μ°[Fe(OH)3]=−641 kJ mol−1 and A0=−243.9 kJ mol−1 at the average temperature of 9±1°C. The upper limit of occurrence of GR mineral at x=2/3, i.e. Fe3(OH)8, is explained by its unstability vs. α-FeOOH and/or magnetite; Fe(OH)3 is thus a hypothetical compound with a GR structure which cannot be observed. These thermodynamic data and Eh-pH diagrams of Fe(OH)(2+x) can be used most importantly to predict the possibility that GR minerals reduce some anions in contaminated soils. The cases of NO3−, Se(VI) or Cr(VI) are fully illustrated.  相似文献   

18.
A new mineral, ferrotochilinite, ideally 6FeS · 5Fe(OH)2, was found at the Oktyabr’sky Mine, Oktyabr’skoe Cu-Ni deposit, Noril’sk, Krasnoyarsk krai, Siberia, Russia. It is associated with ferrovalleriite, magnetite and Fe-rich, chlorite-like phyllosilicate in the cavities of pentlandite-mooihoekite-cubanite ore with subordinate magnetite and chalcopyrite. Ferrotochilinite occurs as flattened on [001], prismatic to elongated lamellar crystals up to 0.1 × 0.5 × 3.2 mm, typically split and curved. Aggregates (up to 6.5 mm in size) are fanlike, rosette-like, or chaotic. Ferrotochilinite is dark bronze. The streak is black. The luster is moderately metallic. The Mohs’ hardness is ca. 1; VHN is 13 kg/mm2. Cleavage is {001} perfect, micalike. Individuals are flexible, inelastic. D(calc) = 3.467 g/cm3. In reflected light, ferrotochilinite is gray, with the hue changing from pale beige to bluish; bireflectance is distinct. Anisotropy is distinct, with gray bluish to yellowish beige rotation colors. No internal reflections. Reflectance values [R min-R max, % (λ, nm)] are: 11.6–11.4 (470), 11.2–12.4 (546), 11.1–13.6 (589), 11.0–15.5 (650). The IR spectrum shows the presence of (OH) groups bonded with Fe cations and the absence of H2O molecules. Chemical composition (wt %; electron probe; H content is calculated) is as follows: 0.02 Mg, 61.92 Fe, 0.03 Ni, 0.09 Cu, 19.45 S, 16.3 O, 1.03 H calc; the total is 98.84. The empirical formula calculated on the basis of 6 S atoms is: Mg0.01Fe10.96Ni0.005Cu0.015S6(OH)10.07 = (Fe5.98Cu0.0015Ni0.005)Σ6S6(OH)9.80(Fe 4.89 2+ Mg0.01)Σ4.90(OH)9.80Fe 0.09 3+ (OH)0.27. Ferrotochilinite is monoclinic, space group is C2/m, Cm or C2, the unit-cell dimensions are: a = 5.463(5), b = 15.865(17), c = 10.825(12) Å, β = 93.7(1)°, V = 936(3) Å3, Z = 2. The strongest reflections in the X-ray powder diffraction pattern (d, Å-I[hkl]) are: 10.83-13[001], 5.392-100[002], 3.281-7[023], 2.777-7[150], 2.696-12[004, $20\bar 1$ ], 2.524-12[ $22\bar 1$ , $20\bar 2$ ], 2.152-8[134, 153], 1.837-11[135, $17\bar 3$ ]. Ferrotochilinite is a structural analog of tochilinite, with Fe2+ instead of Mg in the hydroxide part. The type specimen is deposited in Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.  相似文献   

19.
Summary Tourmaline is an ubiquitous constituent in the Pinilla de Fermoselle rare-element pegmatite (Zamora, Spain), as well as in barren pegmatitic and quartz–tourmaline veins inside the associated leucogranite. The rare-element pegmatite shows internal zoning, evolving from a barren facies, in the lower border zone, in contact with the leucogranite, to a Li-rich facies in the upper border zone, close to the host-rocks.Tourmalines from the veins within the leucogranite have highest Mg contents, and belong to the schorl–dravite series. The tourmalines from the rare-element pegmatite mostly belong to the schorl–elbaite series, with chemical compositions within the range of the end-members, whereas the tourmalines associated with the most evolved zone in the pegmatite belong to the elbaite–rossmanite series. The broad compositional range shown by the tourmalines correlates quite well with the pegmatite zoning. The most plausible substitution mechanism for the chemical evolution of tourmalines during crystallization seems to be Mg–1Fe2+1, [X]–1YAl–1XNa–1YFe2+1, for the foitite–schorl series; YFe2+–3YAl1.5YLi1.5, for the schorl–elbaite vector; XNa–1YLi–0.5[X]1YAl0.5, for the elbaite–rossmanite series; and, (OH)1F1 for all the tourmalines except the pink elbaites. This chemical variation in tourmaline is consistent with a crystal fractionation model for the evolution of the Pinilla pegmatite.  相似文献   

20.
Orthorhombic magnesium-iron ludwigite-vonsenite forms a continuous isomorphic series Mg2Fe3+[BO3]O2-Fe 2 2+ Fe[BO3]O2; its composition at the magnesioskarn and other deposits varies from magnesian to ferriferous members. In addition, they demonstrate isovalent substitution of Mn for Mg (in pinakiolite, blatterite, and others) and practically complete substitution of Ni for Mg (in bonaccordite). Ferric iron in the borates is substituted by isovalent Al and Cr. The incorporation of Ti, Sn, Sb, and V via heterovalent substitution has been studied in less detail. Our research revealed new manifestations of Ti-and Sn-bearing borates. They are magnesioludwigite and azoproite with variable Ti content, as well as by Sn-bearing aluminian borates formed via the 2Fe3+ → (Ti4+ + Mg)6+ and/or (Sn4+ + Mg)6+ substitution. The incorporation of pentavalent elements according to the scheme 3Fe3+ → (Sb5+ + 2Mg)9+ or (V5+ + 2Mg)9+ is not excluded. The highest Ti borates were found in the marbles and calciphyres of the Tazheran deposit in the Baikal region and Nalednoe, Dokuchan, and Titovskoe deposits in Yakutia, where azoproites contain more than 50 and even higher 75 mol % of the Mg2(TiMg)0.5[BO3]O2 end member. Aluminum magnesioludwigites from Yakutia and Chukotka simultaneously contain tin and titanium. Mount Brooks, Alaska, contains tin-bearing azoproite or its tin-bearing varieties. New data are reported on Sb-and V-bearing orthoborates. Calciphyres of Alaska contain monoclinic magnesiohulsite (Mg,Fe)2(SnMg) 0.5 6+ [BO3]O2, which is replaced by schoenfliesite MgSn(OH)6. The studied borate occurrences belong to hypabyssal magnesian skarns of the periclase and monticellite metasomatic PT facies at contacts of dolomites with granitoid intrusions of increasing alkalinity or leucocratic granites. Their formation was related to interaction between disequilibrium kotoite and early oxides and spinellides of various compositions, on the one hand, and, on the other hand, to the influx of Ti-and Sn-bearing hydrothermal solutions.  相似文献   

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