The low-temperature behaviour of the ammonium mica: synthetic ND4-tobelite and ND4-phlogopite has been studied by infrared spectroscopy in the far infrared region, from room temperature down to 20 K. Unlike previously studied low-temperature, orientational ordering of the ammonium ion in the interlayer region from the near infrared region (MOOKHERJEE et al. 2002 a, b), the bands in far infrared region do not show significant change on cooling. This indicates that the coupling between ordering of ammonium ions and other structural rearrangements is weak.
Taseqite is a new mineral species found in small cavities in a single hydrothermal, albitite vein on the top of the Taseq slope, in the northern part of the Ilimaussaq alkaline complex, South Greenland. Besides albite the associated minerals include aegirine, analcime, ancylite-(La), calcite, catapleiite, dolomite, ferrobustamite, fluorapatite, hemimorphite, pectolite, sphalerite and strontianite. Taseqite forms clusters of crystals or individual crystals ranging in size from 0.05 by 0.25 to 0.5 by nearly 3 mm. The crystals show combinations of {0001}, {000 (1) over bar}, {11 (2) over bar0}, {10 (1) over bar0}, {01 (1) over bar0}, the latter two only represented by very narrow faces, {10 (1) over bar1}, {01 (1) over bar2}, {00 (1) over bar(1) over bar}, {10 (1) over bar(2) over bar}, all nearly equally developed, and occasionally (0221) and {20 (2) over bar1}; the crystals are platy on {0001}. The colour varies from clove to yellowish brown and lemon yellow; taseqite is transparent and has a vitreous lustre. The Mobs hardness is 5 1/2; taseqite is brittle and shows fair cleavage on {0001}/{000 (1) over bar}. D-meas. = 3.24(1) g/cm(3), D-calc. = 3.20 g/cm(3). Taseqite is uniaxial, optically negative, with n(epsilon) = 1.6378(5) and n(omega) = 1.6494(3) for lambda = 589 nm. The infrared spectrum shows the presence of OH, H2O and CO3. The microprobe analyses gave: Na2O 7.71, K2O 0.23, CaO 8.19, SrO 13.98, MnO 3.02, FeO 3.92, Y2O3 0.28, Ce2O3 0.08, SnO2 0.13, ZrO2 9.89, HfO2 0.32, Nb2O5 4.38, Ta2O5 0.24, SiO2 41.64, Cl 1.91, H2O 0.59 (by stoichiometry determined from crystal structure analysis), O = Cl = -0.43, total = 96.09. The empirical formula, based on 78.14 anions as found in the crystal structure analysis is: (Na8.81Sr4.78K0.17Ce0.02)Sigma(13.78)(Ca5.17Mn0.59Y0.09)(Sigma5.85)(Fe1.93Mn0.92)(Sigma2.85)(Zr2.84Nb0.11Hf0.05)(Sigma3.00)(Nb1.06Ta0.04Sn0.03)(Sigma1.13)Si24.55O73(O1.65OH0.75(H2O)(0.74))(Sigma3.14)(Cl1.91OH0.09)(Sigma2.00); Z = 3The ideal formula is: Na12Sr3Ca6Fe3Zr3NbSi25O73(O,OH,H2O)(3)Cl-2. The strongest lines on the X-ray powder-diffraction pattern [d in Angstrom (l) (hkl)] are: 9.51 (9) (012), 3.43 (9) (131, 223), 3.19 (8) (208), 2.98 (10) (315), 2.86 (10) (404). The unit cell parameters refined from powder data are: a = 14.286(6) and c = 29.99(2) Angstrom, c: a = 2.0993, V = 5300.7 Angstrom(3). The crystal structure was determined by single-crystal X-ray diffraction and refined to R = 0.037. Taseqite crystallizes in the trigonal system, space group R3m, a = 14.2828(6) and c = 30.0222(12) Angstrom, V = 5303.9(4) Angstrom(3). The compatibility index 1 - Kp/Kc is equal to 0.0005, which is rated as superior. Taseqite belongs to the eudialyte group. It is primarily distinguished from other members of the group by the unique combination of dominance of Sr in N(4) and Nb in M(3).
SHRIMP (Sensitive High-Resolution Ion Microprobe) U-Pb ages of zircons from a single sample of mafic eclogite (Punta de li Tulchi, Sardinia, Italy) are reported. The study under cathodoluminescence (CL) reveals two groups of metamorphic zircons and the SHRIMP analyses allow recognition of three ages: 1) 453 +/- 14 Ma; 2) 400 +/- 10 Ma, and 3) 327 +/- 7 Ma. The age of 453 +/- 14 Ma could be that of the magmatic protolith and an age of 327 +/- 7 Ma can reasonably be attributed to the main Variscan collisional event in Sardinia, which produced Barrovian-type metamorphism, and retrogression of eclogite under amphibolite-facies metamorphism. The intermediate age 400 +/- 10 Ma is difficult to interpret and it could represent either the age of the eclogite facies metamorphism or it is a result of Pb-loss during the main Variscan event at 327 +/- 7 Ma.
Kochelite, first described by WEBSKY in 1868 as a new mineral from pegmatite in the Karkonosze granite, SW Poland was considered a product or products of alteration of Zr-rich fergusonite. An investigation of a topotype sample by optical microscopy, back scattered electrons imaging and electron microprobe analysis show that the name kochelite was applied to an artificial mixture of metamict fergusonite and chemically altered partially metamict zircon. A complex pattern of chemical alteration in both fergusonite and zircon occurred due to the action of alkaline hydrothermal solution during albitization of K-feldspars. The second stage of alteration was related to the weathering of the pegmatite.
The paper aims to give details on the phosphate association from the Meresti Cave, Per ani Mountains, Romania. Ca-phosphates (i. e., hydroxylapatite, brushite and ardealite) are the main components of the guano deposit inside this cave. Associated minerals include gypsum, low quartz, 2M1 illite, interstratified kaolinite-illite, calcite and X-ray amorphous iron sesquioxides. Hydroxylapatite {[Ca9.804Mn0.004Mg0.067Fe2+ 0.054K0.002Na0.003](P5.934S0.066)O-23.929(OH)(2.071)} has a = 9.434(3) Angstrom, c = 6.868(3) Angstrom and V = 529.7(3) Angstrom(3), D-x = 3.142 g/cm(3), D = 3.14(1) g/cm(3), omega = 1.647(1) and epsilon = 1.641(1). CO3 bands in the infrared absorption spectrum (nu(3) = 1466 cm(-1), nu(3)' = 1430 cm(-1), nu(2) = 872 cm(-1)) show that hydroxylapatite from Meresti is carbonate-bearing. Brushite has the mean chemical-structural formula [Ca0.984Mn0.002Mg0.009Fe2+ 0.004K0.001Na0.001](HPO4)(0.976)(SO4)(0.024) . 2H(2)O. Both unit cell [a = 5.812(5) Angstrom, b = 15.169(5) Angstrom, c = 6.239(4) Angstrom and beta = 116.35(13)degrees] and physical parameters [D = 2.32(1) g/cm(3), alpha = 1.540(2), beta = 1.546(2), gamma(calc) = 1.551, for 2V(alpha) = 86degrees) characterize a term close to stoichiometry. Ardealite has the mean chemical structural formula {[Ca1.992Mg0.004Fe2+ 0.002K0.001Na0.001](HPO4)(1.021)(SO4)(0.979) 4H(2)O}. Its mean unit-cell parameters are a = 5.718(3) Angstrom, b = 30.998(24) Angstrom, c = 6.248(5) Angstrom and beta = 117.0(5)degrees, and the measured physical constants alpha = 1.529(2), beta = 1.537(2), gamma (calculated for 2V(alpha) = 86degrees) = 1.544, and D = 2.327(3) g/cm(3). The textural relationships between the three calcium phosphates, observed by scanning electron microscopy and energy-dispersive electron microprobe analysis, suggests that their sequence of crystallization was from hydroxylapatite to brushite and finally ardealite. All the three species clearly resulted from the reaction between the strongly acidic solutions derived from the guano mass and the cave floor or moon-milk flows.
La Salvadora ore deposit (35degrees21' 16"S; 68degrees23'22"W), located in the Province of Mendoza, Argentina, is part of a group of polymetallic veins linked to a porphyry copper that shows a crude temperature zonation away from the potassic centre. This porphyry deposit is genetically related to Lower Permian volcanic rocks from a subduction tectonic setting. La Salvadora is a quartz and carbonate vein deposit hosted by a sericitized, silicified and carbonatized rhyolite. The ore paragenesis is composed of galena, chalcocite, native silver, chalcopyrite, and bornite, along with minor stromeyerite, tetrahedrite, sphalerite and hematite. Myrmekitic intergrowths of galena - rhombic chalcocite, with irregular stromeyerite inclusions in the rhombic chalcocite, are present. Ore mineral analyses show: (i) that the galena is free of silver and copper; (ii) the heterogeneities observed in Pb-free chalcocite are produced by variable contents of silver; (iii) stromeyerite has a very homogeneous composition despite its differences in origins; and, (iv) little copper is observed either in the native silver or in sphalerite. The myrmekitic intergrowths and the stromeyerite inclusions in the chalcocite suggest that they precipitated from fluids at temperatures between 150degrees and 67degreesC, which is supported by the morphology of the fluid inclusions which suggest temperatures of formation below 120degreesC, typical of epithermal systems.
The Thauthe meteorite that fell in July 2002 contains small grains ( < 3 μm) of berthierite and stibnite. These antimony-bearing phases were identified by aid of energy dispersive and wavelength dispersive X-ray spectrometry. This is the first reported occurrence of antimony sulphides in a meteorite.
The structure of clinobarylite, BaBe2Si2O7, a rare mineral from the Khibina alkaline massif, Kola peninsula, has been refined in the orthorhombic space group Pmn2(1), R1 = 0.030 (wR2 = 0.082, S = 1.167) for 469 unique observed reflections with \F-o\ greater than or equal to 4sigma(F). The structure is based upon tetrahedral framework consisting of BeO4 and SiO4 tetrahedra. BeO4 tetrahedra share corners to form chains parallel to the c axis. The chains are interlinked by the Si2O7 groups oriented parallel to the a axis. The Ba2+ cations are in the framework channels and are coordinated by eleven O atoms. The obtained orthorhombic symmetry of clinobarylite is in contradiction with the monoclinic symmetry recently reported for this mineral by CHUKA-NOV et al. (2003). Optical properties and powder X-ray diffraction pattern of clinobarylite have been re-studied and no contradictions with orthorhombic symmetry have been observed. Comparison of clinobarylite and its dimorph, barylite, show that tetrahedral frameworks in the structures of these minerals are based upon tetrahedral sheets of the same type. According to this description, barylite and clinobarylite can be considered as 2O- and 1O-polytypes of BaBe2Si2O7, respectively.
Phase equilibrium in the Cu-Fe-S system has been investigated for over 100 samples by the sealed silica tube method at 800degreesC. Bornite shows solid solutions ranging from (Cu4.70Fe1.30)(6.00)S-4.00 to (Cu7.43Fe0.00)(7.43)S-4.00, and those of pyrrhotite ranges from (Cu0.04Fe1.01)(1.05)S-1.00 to (Cu0.00Fe1.00)(1.00)S-1.00. The intermediate solid solution (iss) and the sulfide liquid exist in the central part of this system. The most important difference between the phase diagram obtained in this study with that reported by KULLERUD et al. (1969) is that the sulfide liquid is between bornite and pyrrhotite, and that the tie-lines between bornite and iss and between bornite and pyrrhotite are unstable. The new phase diagram of this system at 800degreesC is reported.
The Azna granitoid is one of the western Iranian granitoid suite members, which intruded into the Mesozoic regional metamorphic rocks of the Sanandaj-Sirjan metamorphic belt. The structural relations and petrofabric features indicate that the pluton intruded during the main deformational phase in the area. The rocks have sub-alkaline, peraluminous and S-type magmatic characteristic High-grade metamorphic restitic enclaves, rich in biotite, are abundant within the granitoid rocks. The Azna granitoid pluton was generated in a syn-collisional ? setting due to the collision of the Afro-Arabian continental plate and the Central Iranian microplate during the Laramide orogeny.
Samples of kotoite from three boron-bearing magnesian skarns in Romania (Baita Bihor, Pietroasa and Cacova Ierii) were investigated in order to add new data on this rare mineral species and to assess the influence of the chemical variation on the main physical and crystallographic constants of the mineral. In all three occurrences, the mineral is present in the outer skarn zones developed at the contact of igneous bodies of Upper Cretaceous - Paleocene age with dolomite sequences. The grains of kotoite are typically rounded and coated by thin seams of brucite. The compositional limits are given by 0.006 to 0.018 apfu Fe and 0.001 to 0.018 apfu Mn at Baita Bihor, 0.016 to 0.017 apfu Fe and 0.003 to 0.004 apfu Mn at Pietroasa and 0.046 to 0.063 apfu Fe and 0.004 to 0.007 apfu Mn at Cacova Ierii. All the analyzed samples are Ca-poor. The increasing (Fe,Mn)-for-Mg substitution in kotoite causes an increase of the density, mean index of refraction, a cell parameter and cell volume; on the contrary, the c cell parameter decreases with increasing weighed ionic radius of the six-fold coordinated cations, then decreases with advancing (Fe,Mn)-for-Mg substitution. It is reasonable to assume that in all three occurrences kotoite crystallized in the temperature range of 400-575 degreesC, at pressures of up to 3 kbar. Subsequent alteration in szaibelyite+brucite or, more frequently, in brucite+sassolite, was influenced by the pH of the late hydrothermal solutions.
Several banded Australian opal-AG samples were analysed by laser ablation ICP-MS. The banded opals studied contained darker-coloured black or grey bands adjacent to lighter-coloured white or clear bands. The elemental distribution between bands indicated that darker-coloured bands contained significantly higher concentrations of transition elements (Ti, Co, V, Ni, Cu, Zn and Y) and rare-earth elements (La, Cc) than lighter-coloured bands. A solution depletion model, involving the charge-neutralisation of silica colloids by highly-charged transition metal cations, is proposed to explain these results. Irrespective of the origin of the opal, the distribution of trace elements for the white, translucent and play of colour opal bands was observed to be similar. This similarity was consistent with the proposed model.
Ion exchange was used to determine uranium oxidation states in Ce-allanites, fergusonite and monazite contained in Svecofennian granitic pegmatites from Finland. In allanites, uranium was partly oxidized; U(IV)/U t o t range from 0.33 to 0.43. The minerals were metamictic. Fergusonite was found to be totally oxidized, giving 0.06 for the U(IV)/U t o t . The low ratio is assumed to be due mainly to the hydration of fergusonite. Of the samples analysed, the fergusonite and one allanite were from the same pegmatite, but they gave a different degree of oxidation for uranium. This finding may reflect the greater stability of allanite as compared to fergusonite. The monazite was indirectly found to be in reduced form (U(IV)/U t o t 0.93). The method applied probably dissolved only the soluble oxidized form of uranium.
Raman spectroscopy has been used to study a selection of vivianites from different origins. A band is identified at around 3480 cm(-1) whose intensity is sample dependent. The band is attributed to the stretching vibration of Fe3+ OH units which are formed through the autooxidation of the vivianite minerals either by self-oxidation or by photocatalytic oxidation according to the reaction:(Fe2+)(3)(PO4)(2) . 8H(2)O + 1/2O(2) --> (Fe2+)(3-x)(Fe3+)(x)(PO4)(2)(OH)(x) . (8-x)H2Oin which some of the water of crystallization is converted to hydroxyl anions.Complexity of the OH stretching region through the overlap of broad bands is reflected in the water HOH deformation modes at 1660 cm(-1). Using the infrared bands at 3281, 3105 and 3025 cm(-1), hydrogen bond distances of 2.734(5), 2.675(2) and 2.655(2) Angstrom are calculated. Vivianites are characterised by an intense band at 950 cm(-1) assigned to the PO4 symmetric stretching vibration. Low Raman intensity bands are observed at similar to1077, similar to1050, 1015 and similar to985 cm(-1) assigned to the phosphate PO4 antisymmetric stretching vibrations. Multiple antisymmetric stretching vibrations are due to the reduced tetrahedral symmetry. This loss of degeneracy is also reflected in the bending modes. Two bands are observed at similar to423 and similar to456 cm(-1) assigned to the nu(2) bending modes. For the vivianites four bands are observed at similar to584, similar to571, similar to545 and similar to525 cm(-1) assigned to the nu(4) modes of vivianite.
The thermal decomposition of natural ammonium oxalate known as oxammite has been studied using a combination of high resolution thermogravimetry coupled to an evolved gas mass spectrometer and Raman spectroscopy coupled to a thermal stage. Three mass loss steps were found at 57, 175 and 188 °C attributed to dehydration, ammonia evolution and carbon dioxide evolution respectively. Raman spectroscopy shows two bands at 3235 and 3030 cm - 1 attributed to the OH stretching vibrations and three bands at 2995, 2900 and 2879 cm - 1 , attributed to the NH vibrational modes. The thermal degradation of oxammite may be followed by the loss of intensity of these bands. No intensity remains in the OH stretching bands at 100 °C and the NH stretching bands show no intensity at 200 °C. Multiple CO symmetric stretching bands are observed at 1473, 1454, 1447 and 1431 cm - 1 , suggesting that the mineral oxammite is composed of a mixture of chemicals including ammonium oxalate dihydrate, ammonium oxalate monohydrate and anhydrous ammonium oxalate.
In the Early Miocene zeolitized volcanicalstic rocks from NW part of Hrvatsko zagorje green authigenic mica occurs in thin veins and coatings of glass shard vesicles. X-ray powder pattern with widened but still relatively sharp reflections is characteristic for 1M micas, with Fe-rich octahedral sheet. The observed value d((060)) is 1.508 Angstrom. IR spectrum is characterized by sharp absorption bands in the OH stretching region, with two strongest bands at 3580 cm(-1) and 3600 cm(-1) ascribed to Al- Fe3+ and Al-Mg cationic environment of the OH groups. Microprobe analyses revealed that this is an interlayer-deficient dioctahedral mica, with Al as dominant cation in octahedral sheet, M-vi(3+)>1.2, and low tetrahedral substitution, with quite peculiar chemical composition that does not correspond ideally to any member of the mica group.
One hundred and five chemical analyses of augite were used to calculate an average end-members composition (mol. %). The end-members composition consists of: CaMg(Si2O6) - 64%, FeFe(Si2O6) - 19%, with Al-[IV] - 10%, others - %. Some ferroaugite have two dominant end-members CaMgSi2O6 (39 mol. %) and CaFeSi2O6 (29 mol. %). An average subcalcic augite consists of FeMg(Si2O6) (47mol. %) and CaMgSi2O6 (29 mol. %). Titanium has a charge of 4+ in all augites. A maximum CaFe3+ AlSiO6 content (average 22 mol. %) is typical for ferrian augite, but the major end-member is CaMgSi2O6 (63 mol. %). During chemical evolution of augite in the Skaergaard intrusion Fe2+ initially fills both the M(1) and M(2) positions, and later Fe2+ preferentially fills the M(1) position. For pigeonite, Fe2+ tends to occupy progressively the M(2) site.
Nb-containing titanite, Si-[4](1.000) ([6])(Ti-0.748 Al-0.095 Zr-0.045 Nb-0.041 Ta-0.001 Fe-0.067(3+) Sn-0.002 Sb-0.001)(1.000) ([7])(Ca-0.986 Ce-0.004 La-0.001 Mn-0.004 Na-0.005 K-0.001)(1.001) F-0.055 (OH)(0.065) O-4.880, from San Vito quarry, Mt. Somma, Naples, Italy, is characterised by extensive substitutions in the six- and seven-fold coordination sites. Single-crystal X-ray diffraction study indicates this niobian titanite to be monoclinic (a = 6.557(l), b = 8.701 (1), c = 7.077(l) Angstrom, beta = 113.86degrees) with C2/c symmetry. Crystal structure refinement (agreement factor, R = 0.027) suggests that the substitution mechanism (Al, Fe)(3+) + (Nb, Ta)(5+) = 2Ti(4+) is primarily responsible for the incorporation of pentavalent metal ions in the octahedral site.
Pure phases of several di-octahedral (muscovite, Ca and Na-montmorillonites) and tri-octahedral (phlogopite, vermiculite and hectorite) T-O-T phyllosilicates have been studied by FT-Raman spectroscopy to determine whether there are characteristic vibrations for each family of minerals. The samples were first characterized by X-ray powder diffraction and then underwent Raman spectroscopy. spectral region 95-1200 cm(-1). The results revealed a band produced by the symmetric stretching modes of the SiO4 tetrahedra occurring near 680 cm(-1) for the tri-octahedral phyllosilicates. and an equivalent band for di-octahedral phyllosilicates occurring near 700 cm(-1). Another diagnostic pattern allowing rapid identification of the minerals studied is created by bands corresponding to the antisymmetric stretching modes of the SiO4 tetrahedra and to the vibrations of the O-H-O groups.
Raman spectroscopy at ambient and liquid nitrogen temperature has been used to determine the molecular structure of selected minerals from the autunite and meta-autunite groups. Six hydroxyl stretching bands for autunite are observed of which three are highly polarised. The hydroxyl stretching vibrations are related to the strength of hydrogen bonding of the water units. Bands in the Raman spectrum of autunite at 998, 842 and 820 cm–1 are highly polarised. Low intensity band at 915 cm–1 is attributed to the 3 antisymmetric stretching vibration of (UO2)2+ units. The band at 820 cm–1 is attributed to the 1 symmetric stretching mode of the (UO2)2+ units. The (UO2)2+ bending modes are found at 295 and 222 cm–1. The presence of phosphate and arsenate anions and their isomorphic substitution are readily determined by Raman spectroscopy. The collection of Raman spectra at 77 K enables excellent band separation.
