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1.
N. V. Chukanov S. Encheva P. Petrov I. V. Pekov D. I. Belakovskiy S. N. Britvin S. M. Aksenov 《Geology of Ore Deposits》2016,58(8):666-673
Dachiardite-K (IMA No. 2015-041), a new zeolite, is a K-dominant member of the dachiardite series with the idealized formula (К2Са)(Al4Si20O48) · 13H2О. It occurs in the walls of opal–chalcedony veinlets cutting hydrothermally altered effusive rocks of the Zvezdel paleovolcanic complex near the village of Austa, Momchilgrad Municipality, Eastern Rhodopes, Bulgaria. Chalcedony, opal, dachiardite-Ca, dachiardite-Na, ferrierite-Mg, ferrierite-K, clinoptilolite-Ca, clinoptilolite-K, mordenite, smectite, celadonite, calcite, and barite are associated minerals. The mineral forms radiated aggregates up to 8 mm in diameter consisting of split acicular individuals. Dachiardite-K is white to colorless. Perfect cleavage is observed on (100). D meas = 2.18(2), D calc = 2.169 g/cm3. The IR spectrum is given. Dachiardite-K is biaxial (+), α = 1.477 (calc), β = 1.478(2), γ = 1.481(2), 2V meas = 65(10)°. The chemical composition (electron microprobe, mean of six point analyses, H2O determined by gravimetric method) is as follows, wt %: 4.51 K2O, 3.27 CaO, 0.41 BaO, 10.36 A12O3, 67.90 SiO2, 13.2 H2O, total is 99.65. The empirical formula is H26.23K1.71Ca1.04Ba0.05Al3.64Si20.24O61. The strongest reflections in the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.76 (24) (001), 8.85 (58) (200), 4.870 (59) (002), 3.807 (16) (202), 3.768 (20) (112, 020), 3.457 (100) (220), 2.966 (17) (602). Dachiardite-K is monoclinic, space gr. C2/m, Cm or C2; the unit cell parameters refined from the powder X-ray diffraction data are: a = 18.670(8), b = 7.511(3), c = 10.231(4) Å, β = 107.79(3)°, V= 1366(1) Å3, Z = 1. The type specimen has been deposited in the Earth and Man National Museum, Sofia, Bulgaria, with the registration number 23927. 相似文献
2.
I. V. Pekov N. V. Zubkova N. V. Chukanov A. E. Zadov V. G. Grishin D. Yu. Pushcharovsky 《Geology of Ore Deposits》2010,52(7):584-590
A new mineral, yegorovite, has been identified in the late hydrothermal, low-temperature assemblage of the Palitra hyperalkaline pegmatite at Mt. Kedykverpakhk, Lovozero alkaline pluton, Kola Peninsula, Russia. The mineral is intimately associated with revdite and megacyclite, earlier natrosilite, microcline, and villiaumite. Yegorovite occurs as coarse, usually split prismatic (up to 0.05 × 0.15 × 1 mm) or lamellar (up to 0.05 × 0.7 × 0.8 mm) crystals. Polysynthetic twins and parallel intergrowths are typical. Mineral individuals are combined in bunches or chaotic groups (up to 2 mm); radial-lamellar clusters are less frequent. Yegorovite is colorless, transparent with vitreous luster. Cleavage is perfect parallel to (010) and (001). Fracture is splintery; crystals are readily split into acicular fragments. The Mohs hardness is ~2. Density is 1.90(2) g/cm3 (meas) and 1.92 g/cm3 (calc). Yegorovite is biaxial (?), with α = 1.474(2), β = 1.479(2), and γ = 1.482(2), 2V meas > 70°, 2V calc = 75°. The optical orientation is X ∧ a ~ 15°, Y = c, Z = b. The IR spectrum is given. The chemical composition determined using an electron microprobe (H2O determined from total deficiency) is (wt %): 23.28 Na2O, 45.45 SiO2, 31.27 H2Ocalc; the total is 100.00. The empirical formula is Na3.98Si4.01O8.02(OH)3.98 · 7.205H2O. The idealized formula is Na4[Si4O8(OH)4] · 7H2O. Yegorovite is monoclinic, space group P21/c. The unit-cell dimensions are a = 9.874, b= 12.398, c = 14.897 Å, β = 104.68°, V = 1764.3 Å3, Z = 4. The strongest reflections in the X-ray powder pattern (d, Å (I, %)([hkl]) are 7.21(70)[002], 6.21(72)[012, 020], 4.696(44)[022], 4.003(49)[211], 3.734(46)[\(\bar 2\) 13], 3.116(100)[024, 040], 2.463(38)[\(\bar 4\)02, \(\bar 2\)43]. The crystal structure was studied by single-crystal method, R hkl = 0.0745. Yegorovite is a representative of a new structural type. Its structure consists of single chains of Si tetrahedrons [Si4O8(OH)4]∞ and sixfold polyhedrons of two types: [NaO(OH)2(H2O)3] and [NaO(OH)(H2O)4] centered by Na. The mineral was named in memory of Yu. K. Yegorov-Tismenko (1938–2007), outstanding Russian crystallographer and crystallochemist. The type material of yegorovite has been deposited at the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow. 相似文献
3.
Michail N. Taran Haruo Ohashi Monika Koch-Müller 《Physics and Chemistry of Minerals》2008,35(3):117-127
Six synthetic NaScSi2O6–CaNiSi2O6 pyroxenes were studied by optical absorption spectroscopy. Five of them of intermediate (Na1−x
, Ca
x
)(Sc1−x
, Ni
x
)Si2O6 compositions show spectra typical of Ni2+ in octahedral coordination, more precise Ni2+ at the M1 site of the pyroxene structure. The common feature of all spectra is three broad absorption bands with maxima around
8,000, 13,000 and 24,000 cm−1 assigned to 3
A
2g → 3
T
2g, 3
A
2g → 3
T
1g and →3
T
1g (3
P) electronic spin-allowed transitions of VINi2+. A weak narrow peak at ∼14,400 cm−1 is assigned to the spin-forbidden 3
A
2g → 1
T
2g (1
D) transition of Ni2+. Under pressure the spin-allowed bands shift to higher energies and change in intensity. The octahedral compression modulus,
calculated from the shift of the 3
A
2g → 3
T
2g band in the (Na0.7Ca0.3)(Sc0.7Ni0.3)Si2O6 pyroxene is evaluated as 85±20 GPa. The Racah parameter B of Ni2+(M1) is found gradually changing from ∼919 cm−1 at ambient pressure to ∼890 cm−1 at 6.18 GPa. The Ni end-member pyroxene [(Ca0.93 Ni0.07)NiSi2O6] has a spectrum different from all others. In addition to the above mentioned bands of Ni2+(M1) it displays several new relatively intense and broad extra bands, which were attributed to electronic transitions of
Ni2+ at the M2 site. In difference to CaO8 polyhedron geometry of an eightfold coordination, Ni2+(M2)O8 polyhedra are assumed to be relatively large distorted octahedra. Due to different distortions and different compressibilities
of the M1 and M2 sites the Ni2+(M1)- and Ni2+(M2)-bands display rather different pressure-induced behaviors, becoming more resolved in the high-pressure spectra than in
that measured at atmospheric pressure. The octahedral compression modulus of Ni2+(M1) in this end-member pyroxene is evaluated as 150 ± 25 GPa, which is noticeably larger than in Ni0.3 pyroxene. This is due to a smaller size and, thus, a stiffer character of Ni2+(M1)O6 octahedron in the (Ca0.93Ni0.07)NiSi2O6 pyroxene compared to (Na0.7Ca0.3)(Sc0.7Ni0.3)Si2O6.
相似文献
Monika Koch-MüllerEmail: |
4.
We carried out reversed piston-cylinder experiments on the equilibrium paragonite = jadeite + kyanite + H2O at 700°C, 1.5–2.5 GPa, in the presence of H2O-NaCl fluids. Synthetic paragonite and jadeite and natural kyanite were used as starting materials. The experiments were performed on four different nominal starting compositions: X(H2O)=1.0, 0.90, 0.75 and 0.62. Reaction direction and extent were determined from the weight change in H2O in the capsule, as well as by optical and scanning electron microscopy (SEM). At X(H2O)=1.0, the equilibrium lies between 2.25 and 2.30 GPa, in good agreement with the 2.30–2.45 GPa reversal of Holland (Contrib Miner Petrol 68:293–301, 1979). Lowering X(H2O) decreases the pressure of paragonite breakdown to 2.10–2.20 GPa at X(H2O)=0.90 and 1.85–1.90 GPa at X(H2O)=0.75. The experiments at X(H2O) = 0.62 yielded the assemblage albite + corundum at 1.60 GPa, and jadeite + kyanite at 1.70 GPa. This constrains the position of the isothermal paragonite–jadeite–kyanite–albite–corundum–H2O invariant point in the system Na2O–Al2O3–SiO2–H2O to be at 1.6–1.7 GPa and X(H2O)~0.65±0.05. The data indicate that H2O activity, a(H2O), is 0.75–0.86, 0.55–0.58, and <0.42 at X(H2O)=0.90, 0.75, and 0.62, respectively. These values approach X(H2O)2, and agree well with the a(H2O) model of Aranovich and Newton (Contrib Miner Petrol 125:200–212, 1996). Our results demonstrate that the presence or absence of paragonite can be used to place limits on a(H2O) in high-pressure metamorphic environments. For example, nearly pure jadeite and kyanite from a metapelite from the Sesia Lanzo Zone formed during the Eo-Alpine metamorphic event at 1.7–2.0 GPa, 550–650°C. The absence of paragonite requires a fluid with low a(H2O) of 0.3–0.6, which could be due to the presence of saline brines. 相似文献
5.
Middendorfite, a new mineral species, has been found in a hydrothermal assemblage in Hilairite hyperperalkaline pegmatite at the Kirovsky Mine, Mount Kukisvumchorr apatite deposit, Khibiny alkaline pluton, Kola Peninsula, Russia. Microcline, sodalite, cancrisilite, aegirine, calcite, natrolite, fluorite, narsarsukite, labuntsovite-Mn, mangan-neptunite, and donnayite are associated minerals. Middendorfite occurs as rhombshaped lamellar and tabular crystals up to 0.1 × 0.2 × 0.4 mm in size, which are combined in worm-and fanlike segregations up to 1 mm in size. The color is dark to bright orange, with a yellowish streak and vitreous luster. The mineral is transparent. The cleavage (001) is perfect, micalike; the fracture is scaly; flakes are flexible but not elastic. The Mohs hardness is 3 to 3.5. Density is 2.60 g/cm3 (meas.) and 2.65 g/cm3 (calc.). Middendorfite is biaxial (?), α = 1.534, β = 1.562, and γ = 1.563; 2V (meas.) = 10°. The mineral is pleochroic strongly from yellowish to colorless on X through brown on Y and to deep brown on Z. Optical orientation: X = c. The chemical composition (electron microprobe, H2O determined with Penfield method) is as follows (wt %): 4.55 Na2O, 10.16 K2O, 0.11 CaO, 0.18 MgO, 24.88 MnO, 0.68 FeO, 0.15 ZnO, 0.20 Al2O3, 50.87 SiO2, 0.17 TiO2, 0.23 F, 7.73 H2O; ?O=F2?0.10, total is 99.81. The empirical formula calculated on the basis of (Si,Al)12(O,OH,F)36 is K3.04(Na2.07Ca0.03)Σ2.10(Mn4.95Fe0.13Mg0.06Ti0.03Zn0.03)Σ5.20(Si11.94Al0.06)Σ12O27.57(OH)8.26F0.17 · 1.92H2O. The simplified formula is K3Na2Mn5Si12(O,OH)36 · 2H2O. Middenforite is monoclinic, space group: P21/m or P21. The unit cell dimensions are a = 12.55, b = 5.721, c = 26.86 Å; β = 114.04°, V = 1761 Å3, Z = 2. The strongest lines in the X-ray powder pattern [d, Å, (I)(hkl)] are: 12.28(100)(002), 4.31(81)(11\(\overline 4 \)), 3.555(62)(301, 212), 3.063(52)(008, 31\(\overline 6 \)), 2.840(90)(312, 021, 30\(\overline 9 \)), 2.634(88)(21\(\overline 9 \), 1.0.\(\overline 1 \)0, 12\(\overline 4 \)), 2.366(76)(22\(\overline 6 \), 3.1.\(\overline 1 \)0, 32\(\overline 3 \)), 2.109(54)(42–33, 42–44, 51\(\overline 9 \), 414), 1.669(64)(2.2.\(\overline 1 \)3, 3.2.\(\overline 1 \)3, 62\(\overline 3 \), 6.1.\(\overline 1 \)3), 1.614(56)(5.0.\(\overline 1 \)6, 137, 333, 71\(\overline 1 \)). The infrared spectrum is given. Middendorfite is a phyllosilicate related to bannisterite, parsenttensite, and the minerals of the ganophyllite and stilpnomelane groups. The new mineral is named in memory of A.F. von Middendorff (1815–1894), an outstanding scientist, who carried out the first mineralogical investigations in the Khibiny pluton. The type material of middenforite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. 相似文献
6.
Experimental investigations in the system rare-metal granite–Na2O–SiO2–H2O with the addition of aqueous solutions containing Rb, Cs, Sn, W, Mo, and Zn at 600°C and 1.5 kbar showed that the typical elements of rare-metal granites (Li, Rb, Cs, Be, Nb, and Ta) are preferentially concentrated in hydrosilicate liquids coexisting with aqueous fluid. The same behavior is characteristic of Zn and Sn, the minerals of which are usually formed under hydrothermal conditions. In contrast, Mo and W are weakly extracted by hydrosilicate liquids and almost equally distributed between them and aqueous fluids. Liquids similar to those described in this paper are formed during the final stages of magmatic crystallization in granite and granitepegmatite systems. The formation of hydrosilicate liquids in late magmatic and postmagmatic processes will be an important factor controlling the redistribution of metal components between residual magmatic melts, minerals, and aqueous fluids and, consequently, the mobility of these components in fluid-saturated magmatic systems enriched in rare metals. 相似文献
7.
The specific heat capacity (C p) of six variably hydrated (~3.5 wt% H2O) iron-bearing Etna trachybasaltic glasses and liquids has been measured using differential scanning calorimetry from room temperature across the glass transition region. These data are compared to heat capacity measurements on thirteen melt compositions in the iron-free anorthite (An)–diopside (Di) system over a similar range of H2O contents. These data extend considerably the published C p measurements for hydrous melts and glasses. The results for the Etna trachybasalts show nonlinear variations in, both, the heat capacity of the glass at the onset of the glass transition (i.e., C p g ) and the fully relaxed liquid (i.e., C p l ) with increasing H2O content. Similarly, the “configurational heat capacity” (i.e., C p c = C p l ? C p g ) varies nonlinearly with H2O content. The An–Di hydrous compositions investigated show similar trends, with C p values varying as a function of melt composition and H2O content. The results show that values in hydrous C p g , C p l and C p c in the depolymerized glasses and liquids are substantially different from those observed for more polymerized hydrous albitic, leucogranitic, trachytic and phonolitic multicomponent compositions previously investigated. Polymerized melts have lower C p l and C p c and higher C p g with respect to more depolymerized compositions. The covariation between C p values and the degree of polymerization in glasses and melts is well described in terms of SMhydrous and NBO/T hydrous. Values of C p c increase sharply with increasing depolymerization up to SMhydrous ~ 30–35 mol% (NBO/T hydrous ~ 0.5) and then stabilize to an almost constant value. The partial molar heat capacity of H2O for both glasses (\( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{g}} \)) and liquids (\( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \)) appears to be independent of composition and, assuming ideal mixing, we obtain a value for \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \) of 79 J mol?1 K?1. However, we note that a range of values for \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \) (i.e., ~78–87 J mol?1 K?1) proposed by previous workers will reproduce the extended data to within experimental uncertainty. Our analysis suggests that more data are required in order to ascribe a compositional dependence (i.e., nonideal mixing) to \( C_{{{\text{p}}\;{\text{H}}_{2} {\text{O}}}}^{\text{l}} \). 相似文献
8.
Ekaterina A. Sirotkina Andrey V. Bobrov Anna V. Spivak Luca Bindi Dmitry Yu. Pushcharovsky 《Physics and Chemistry of Minerals》2016,43(10):731-738
A new pyroxene with formula (Na0.86Mg0.14)(Mg0.57Ti0.43)Si2O6, synthesized in a high-pressure toroidal ‘anvil-with-hole’ apparatus at P = 7 GPa and T = 1700 °C, was characterized by X-ray single-crystal diffraction and Raman spectroscopy. The compound was found to be monoclinic (R1 = 2.56 %), space group C2/c, with lattice parameters a = 9.687(2), b = 8.814(1), c = 5.290(1) Å, β = 107.853(2)°, V = 430.08(1) Å3. The coexistence of Mg and Ti4+ at the M1 site does not induce strong modifications either to the M1 site or to the adjacent M2 site. The Raman spectrum of synthetic Na–Ti-pyroxene was obtained for the first time and compared with that of Mg2Si2O6 (with very low concentrations of Na and Ti). The structural characterization of the Na–Ti–Mg-pyroxene is important, because the study of its thermodynamic constants provides new constraints on thermobarometry of the upper mantle assemblages. 相似文献
9.
I. V. Pekov N. V. Chukanov V. O. Yapaskurt D. I. Belakovskiy I. S. Lykova N. V. Zubkova E. P. Shcherbakova S. N. Britvin A. D. Chervonnyi 《Geology of Ore Deposits》2017,59(7):609-618
Based on a study of samples found in the Khibiny (Mt. Rasvumchorr: the holotype) and Lovozero (Mts Alluaiv and Vavnbed) alkaline complexes on the Kola Peninsula, Russia, tinnunculite was approved by the IMA Commission on New Minerals, Nomenclature, and Classification as a valid mineral species (IMA no. 2015-02la) and, taking into account a revisory examination of the original material from burnt dumps of coal mines in the southern Urals, it was redefined as crystalline uric acid dihydrate (UAD), C5H4N4O3 · 2H2O. Tinnunculite is poultry manure mineralized in biogeochemical systems, which could be defined as “guano microdeposits.” The mineral occurs as prismatic or tabular crystals up to 0.01 × 0.1 × 0.2 mm in size and clusters of them, as well as crystalline or microglobular crusts. Tinnunculite is transparent or translucent, colorless, white, yellowish, reddish or pale lilac. Crystals show vitreous luster. The mineral is soft and brittle, with a distinct (010) cleavage. Dcalc = 1.68 g/cm3 (holotype). Tinnunculite is optically biaxial (–), α = 1.503(3), β = 1.712(3), γ = 1.74(1), 2Vobs = 40(10)°. The IR spectrum is given. The chemical composition of the holotype sample (electron microprobe data, content of H is calculated by UAD stoichiometry) is as follows, wt %: 37.5 О, 28.4 С, 27.0 N, 3.8 Hcalc, total 96.7. The empirical formula calculated on the basis of (C + N+ O) = 14 apfu is: C4.99H8N4.07O4.94. Tinnunculite is monoclinic, space group (by analogy with synthetic UAD) P21/c. The unit cell parameters of the holotype sample (single crystal XRD data) are a = 7.37(4), b = 6.326(16), c = 17.59(4) Å, β = 90(1)°, V = 820(5) Å3, Z = 4. The strongest reflections in the XRD pattern (d, Å–I[hkl]) are 8.82–84[002], 5.97–15[011], 5.63–24[102?, 102], 4.22–22[112], 3.24–27[114?,114], 3.18–100[210], 3.12–44[211?, 211], 2.576–14[024]. 相似文献
10.
11.
The join CaMgSi2O6–KAlSi3O8 has been studied at 6 GPa (890–1,500°C) and 3.5 GPa (1,000–1,100°C). K-rich melts in the join produce assemblages Cpx + Grt, Cpx + Opx, Cpx + San, and Cpx + Grt + San at 1,100–1,300°C. At NSansystem<~70 mol%, sanidine is unstable on the solidus and appears at the liquidus, if NSansystem>90 mol%. This explains a scarcity of San in mantle Cpx-rich assemblages and its association with high-K aluminosilicate melt inclusions in diamonds. In absence of San, KCpx is the only host for potassium. The K-jadeite content in KCpx systematically increases with decreasing temperature and reaches 10–12 mol% near the solidus. However, KCpx coexists with San at NSansystem>70 mol% and <1,300°C, being formed via reaction San + L=KCpx. The KJd content in KCpx is controlled by the equilibrium San=KJd + SiO2L that displaces to the right with increasing pressure and decreasing both the temperature and
This equilibrium is considered to be responsible for the formation of San lamellae in natural UHP Cpx. In our experiments at 3.5 GPa, garnet is absent whereas the KJd and Ca-Eskola contents in Cpx are low, and the join CaMgSi2O6–KAlSi3O8 is close to binary (with the eutectic Cpx + San + L). Different topologies of the join at 6 and 3.5 GPa define a sequence of mineral crystallization from K-rich aluminosilicate melts during cooling and decompression: from KCpx + Grt without San at P>4 GPa to Cpx + San at P<4 GPa. Similar sequence of assemblages is observed in some eclogitic xenoliths from kimberlites and Grt–Cpx rocks of the Kokchetav Complex (Northern Kazakhstan). 相似文献
12.
Attikaite, a new mineral species, has been found together with arsenocrandalite, arsenogoyazite, conichalcite, olivenite, philipsbornite, azurite, malachite, carminite, beudantite, goethite, quartz, and allophane at the Christina Mine No. 132, Kamareza, Lavrion District, Attiki Prefecture (Attika), Greece. The mineral is named after the type locality. It forms spheroidal segregations (up to 0.3 mm in diameter) consisting of thin flexible crystals up to 3 × 20 × 80 μm in size. Its color is light blue to greenish blue, with a pale blue streak. The Mohs’ hardness is 2 to 2.5. The cleavage is eminent mica-like parallel to {001}. The density is 3.2(2) g/cm3 (measured in heavy liquids) and 3.356 g/cm3 (calculated). The wave numbers of the absorption bands in the infrared spectrum of attikaite are (cm?1; sh is shoulder; w is a weak band): 3525sh, 3425, 3180, 1642, 1120w, 1070w, 1035w, 900sh, 874, 833, 820, 690w, 645w, 600sh, 555, 486, 458, and 397. Attikaite is optically biaxial, negative, α = 1.642(2), β = γ = 1.644(2) (X = c) 2V means = 10(8)°, and 2V calc = 0°. The new mineral is microscopically colorless and nonpleochroic. The chemical composition (electron microprobe, average over 4 point analyses, wt %) is: 0.17 MgO, 17.48 CaO, 0.12 FeO, 16.28 CuO, 10.61 Al2O3, 0.89 P2O5, 45.45 As2O5, 1.39 SO3, and H2O (by difference) 7.61, where the total is 100.00. The empirical formula calculated on the basis of (O,OH,H2O)22 is: Ca2.94Cu 1.93 2+ Al1.97Mg0.04Fe 0.02 2+ [(As3.74S0.16P0.12)Σ4.02O16.08](OH)3.87 · 2.05H2 O. The simplified formula is Ca3Cu2Al2(AsO4)4(OH)4 · 2H2O. Attikaite is orthorhombic, space group Pban, Pbam or Pba2; the unit-cell dimensions are a = 10.01(1), b = 8.199(5), c = 22.78(1) Å, V = 1870(3) Å3, and Z = 4. In the result of the ignition of attikaite for 30 to 35 min at 128–140°, the H2O bands in the IR spectrum disappear, while the OH-group band is not modified; the weight loss is 4.3%, which approximately corresponds to two H2O molecules per formula; and parameter c decreases from 22.78 to 18.77 Å. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %)((hkl)] are: 22.8(100)(001), 11.36(60)(002), 5.01(90)(200), 3.38(5)(123, 205), 2.780(70)(026), 2.682(30)(126), 2.503(50)(400), 2.292(20)(404). The type material of attikaite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. The registration number is 3435/1. 相似文献
13.
A new oxygen-deficient perovskite with the composition Ca(Fe0.4Si0.6)O2.8 has been synthesised at high-pressure and -temperature conditions relevant to the Earths transition zone using a multianvil apparatus. In contrast to pure CaSiO3 perovskite, this new phase is quenchable under ambient conditions. The diffraction pattern revealed strong intensities for pseudocubic reflections, but the true lattice is C-centred monoclinic with a=9.2486 Å, b=5.2596 Å, c=21.890 Å and =97.94°. This lattice is only slightly distorted from rhombohedral symmetry. Electron-diffraction and high-resolution TEM images show that a well-ordered ten-layer superstructure is developed along the monoclinic c* direction, which corresponds to the pseudocubic [111] direction. This unique type of superstructure likely consists of an oxygen-deficient double layer with tetrahedrally coordinated silicon, alternating with eight octahedral layers of perovskite structure, which are one half each occupied by silicon and iron as indicated by Mössbauer and Si K electron energy loss spectroscopy. The maximum iron solubility in CaSiO3 perovskite is determined at 16 GPa to be 4 at% on the silicon site and it increases significantly above 20 GPa. The phase relations have been analysed along the join CaSiO3–CaFeO2.5, which revealed that no further defect perovskites are stable. An analogous phase exists in the aluminous system, with Ca(Al0.4Si0.6)O2.8 stoichiometry and diffraction patterns similar to that of Ca(Fe0.4Si0.6)O2.8. In addition, we discovered another defect perovskite with Ca(Al0.5Si0.5)O2.75 stoichiometry and an eight-layer superstructure most likely consisting of a tetrahedral double layer alternating with six octahedral layers. The potential occurrence of all three defect perovskites in the Earths interior is discussed. 相似文献
14.
G. Ottonello B. Civalleri J. Ganguly M. Vetuschi Zuccolini Y. Noel 《Physics and Chemistry of Minerals》2009,36(2):87-106
Thermophysical properties of the various polymorphs (i.e. α-, β- and γ) of Mg2SiO4 were computed with the CRYSTAL06 code within the framework of CO-LCAO-GTF approach by using the hybrid B3LYP density functional
method. Potential wells were calculated through a symmetry preserving, variable cell-shape structure relaxation procedure.
Vibrational frequencies were computed at the long-wavelength limit corresponding to the center of the Brillouin zone (k → 0). Thermodynamic properties were estimated through a semiclassical approach that combines B3LYP vibrational frequencies
for optic modes and the Kieffer’s model for the dispersion relation of acoustic modes. All computed values except volume (i.e.
electronic energy, zero point energy, optical vibrational modes, thermal corrections to internal energy, standard state enthalpy
and Gibbs free energy of reaction, bulk modulus and its P and T derivatives, entropy, C
V, C
P) are consistent with available experimental data and/or reasonable estimates. Volumes are slightly overestimated relative
to those determined directly by X-ray diffraction. A set of optimized volumetric properties that are consistent with the other
semiclassical properties of the phases α, β and γ have been derived by optimization procedure such that the calculated boundaries
for the α/β and β/γ equilibria have the best overall agreement with the experimental data for these transitions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
G. OttonelloEmail: |
15.
Shi-Hua Sang Rui-Zhi Cui Xue-Ping Zhang Kai-Jie Zhang 《Geochemistry International》2017,55(12):1131-1139
According to the compositions of the underground brine resources in the west of Sichuan Basin, solubilities of the ternary systems NaBr–Na2SO4–H2O and KBr–K2SO4–H2O were investigated by isothermal method at 348 K. The equilibrium solid phases, solubilities of salts, and densities of the solutions were determined. On the basis of the experimental data, the phase diagrams and the density-composition diagrams were plotted. In the two ternary systems, the phase diagrams consist of two univariant curves, one invariant point and two crystallization fields. Neither solid solution nor double salts were found. The equilibrium solid phases in the ternary system NaBr–Na2SO4–H2O are NaBr and Na2SO4, and those in the ternary system KBr–K2SO4–H2O are KBr and K2SO4. Using the solubilities data of the two ternary subsystems at 348 K, mixing ion-interaction parameters of Pitzer’s equation θxxx, Ψxxx and Ψxxx were fitted by multiple linear regression method. Based on the chemical model of Pitzer’s electrolyte solution theory, the solubilities of phase equilibria in the two ternary systems NaBr–Na2SO4–H2O and KBr–K2SO4–H2O were calculated with corresponding parameters. The calculation diagrams were plotted. The results showed that the calculated values have a good agreement with experimental data. 相似文献
16.
G. N. Gamyanin Yu. Ya. Zhdanov N. V. Zayakina V. V. Gamyanina V. S. Suknev 《Geology of Ore Deposits》2007,49(7):514-517
Mangazeite, a new mineral species, has been found at the Mangazeya silver deposit (300 km east of the Lena River, 65°43′40″ N and 130°20′ E) in eastern Yakutia (Sakha Republic, Siberia, Russia). The new mineral was described from fractured, sericitized, and pyritized granodiorite adjacent to a quartz-arsenopyrite vein. Associated minerals are gypsum and chlorite. The new mineral occurs as radial fibrous segregations of thin lamellar crystals. The size of the fibers does not exceed 40 μm in length and 1 μm across. The mineral is white, with a white streak and a vitreous luster. Mangazeite is transparent in isolated grains. No fluorescence is observed. The Mohs hardness is 1–2. The calculated density is 2.15 g/cm3. The new mineral is biaxial; its optical character was not determined; α = 1.525(9), β was not measured, and γ = 1.545(9). The average chemical composition is as follows (wt %): Al2O3 36.28, SO3 28.81, H2O+ 34.35, total 99.44, H2O? 9.27. The H2O? content was neither included in the total nor used in formula calculation. The empirical formula is Al1.99(SO4)1.01(OH)3.94 · 3.37H2O. The simplified formula is Al2(SO4)(OH)4 · 3H2O. The theoretical chemical composition calculated from this formula is (wt %) Al2O3 37.47, SO3 29.42, H2O 33.11, total 100.00. The new mineral is triclinic; the unit cell parameters refined from X-ray powder diffraction data are a = 8.286(5), b = 9.385(5), c = 11.35(1) Å, α = 96.1(1), β = 98.9(1), γ = 96.6(1)°, and Z = 4. The strongest lines in the X-ray powder diffraction pattern (d(I, %)) are 8.14(19), 7.59(49), 7.16(46), 4.258(100), 4.060(48), and 3.912(43). Mangazeite is supergene in origin and crystallized in a favorable aluminosilicate environment in the presence of sulfate ion due to pyrite oxidation. 相似文献
17.
The solubility of chromium in chlorite as a function of pressure, temperature, and bulk composition was investigated in the system Cr2O3–MgO–Al2O3–SiO2–H2O, and its effect on phase relations evaluated. Three different compositions with X Cr = Cr/(Cr + Al) = 0.075, 0.25, and 0.5 respectively, were investigated at 1.5–6.5 GPa, 650–900 °C. Cr-chlorite only occurs in the bulk composition with X Cr = 0.075; otherwise, spinel and garnet are the major aluminous phases. In the experiments, Cr-chlorite coexists with enstatite up to 3.5 GPa, 800–850 °C, and with forsterite, pyrope, and spinel at higher pressure. At P > 5 GPa other hydrates occur: a Cr-bearing phase-HAPY (Mg2.2Al1.5Cr0.1Si1.1O6(OH)2) is stable in assemblage with pyrope, forsterite, and spinel; Mg-sursassite coexists at 6.0 GPa, 650 °C with forsterite and spinel and a new Cr-bearing phase, named 11.5 Å phase (Mg:Al:Si = 6.3:1.2:2.4) after the first diffraction peak observed in high-resolution X-ray diffraction pattern. Cr affects the stability of chlorite by shifting its breakdown reactions toward higher temperature, but Cr solubility at high pressure is reduced compared with the solubility observed in low-pressure occurrences in hydrothermal environments. Chromium partitions generally according to \(X_{\text{Cr}}^{\text{spinel}}\) ? \(X_{\text{Cr}}^{\text{opx}}\) > \(X_{\text{Cr}}^{\text{chlorite}}\) ≥ \(X_{\text{Cr}}^{\text{HAPY}}\) > \(X_{\text{Cr}}^{\text{garnet}}\). At 5 GPa, 750 °C (bulk with X Cr = 0.075) equilibrium values are \(X_{\text{Cr}}^{\text{spinel}}\) = 0.27, \(X_{\text{Cr}}^{\text{chlorite}}\) = 0.08, \(X_{\text{Cr}}^{\text{garnet}}\) = 0.05; at 5.4 GPa, 720 °C \(X_{\text{Cr}}^{\text{spinel}}\) = 0.33, \(X_{\text{Cr}}^{\text{HAPY}}\) = 0.06, and \(X_{\text{Cr}}^{\text{garnet}}\) = 0.04; and at 3.5 GPa, 850 °C \(X_{\text{Cr}}^{\text{opx}}\) = 0.12 and \(X_{\text{Cr}}^{\text{chlorite}}\) = 0.07. Results on Cr–Al partitioning between spinel and garnet suggest that at low temperature the spinel- to garnet-peridotite transition has a negative slope of 0.5 GPa/100 °C. The formation of phase-HAPY, in assemblage with garnet and spinel, at pressures above chlorite breakdown, provides a viable mechanism to promote H2O transport in metasomatized ultramafic mélanges of subduction channels. 相似文献
18.
Linglin Chu Andreas Enggist Robert W. Luth 《Contributions to Mineralogy and Petrology》2011,162(3):565-571
To examine the effect of KCl-bearing fluids on the melting behavior of the Earth’s mantle, we conducted experiments in the
Mg2SiO4–MgSiO3–H2O and Mg2SiO4–MgSiO3–KCl–H2O systems at 5 GPa. In the Mg2SiO4–MgSiO3–H2O system, the temperature of the fluid-saturated solidus is bracketed between 1,200–1,250°C, and both forsterite and enstatite
coexist with the liquid under supersolidus conditions. In the Mg2SiO4–MgSiO3–KCl–H2O systems with molar Cl/(Cl + H2O) ratios of 0.2, 0.4, and 0.6, the temperatures of the fluid-saturated solidus are bracketed between 1,400–1,450°C, 1,550–1,600°C,
and 1,600–1,650°C, respectively, and only forsterite coexists with liquid under supersolidus conditions. This increase in
the temperature of the solidus demonstrates the significant effect of KCl on reducing the activity of H2O in the fluid in the Mg2SiO4–MgSiO3–H2O system. The change in the melting residues indicates that the incongruent melting of enstatite (enstatite = forsterite + silica-rich
melt) could extend to pressures above 5 GPa in KCl-bearing systems, in contrast to the behavior in the KCl-free system. 相似文献
19.
I. V. Pekov S. V. Krivovichev N. V. Chukanov V. O. Yapaskurt E. G. Sidorov 《Geology of Ore Deposits》2016,58(7):568-578
The paper reports new findings of avdoninite from deposits of active fumaroles in the Second Scoria Cone at the Northern Breach of the Great Fissure Tolbachik Eruption, Tolbachik Volcano, Kamchatka Peninsula, Russia. The crystal structure of the mineral has been determined for the first time, which has allowed reliable determination of its space group and unit cell dimensions, refinement of its formula K2Cu5-Cl8(OH)4 · 2H2O, and correct indexing of its X-ray powder diffraction pattern. Avdoninite is monoclinic, space group P21/c, a = 11.592(2), b = 6.5509(11), c = 11.745(2) Å, β = 91.104(6)°, V = 891.8(3) Å3, Z = 2. The crystal structure of this mineral has been determined on a single crystal R 1 [F > 4σ (F)] = 0.063. It is based on sheets of copper–oxo-chloride complexes [Cu5Cl8(OH)4]2– parallel to (100). The K+ cation and H2O molecules are interlayers. 相似文献
20.
The solubility of Gd2Ti2O7 ceramic in acidic solutions (HCl and HClO4) was studied at 250°C and saturation vapor pressure within pH 2.5–5.2. The dissolution process occurs mainly via two reactions: 0.5 Gd2Ti2O7(cr) + 3H+ = Gd3+ + TiO2(cr) + 1.5 H2O at pH < 3 and 0.5Gd2Ti2O7(cr) + H+ + 0.5H2O = Gd(OH) 2 + TiO2(cr) at pH 3–5. The thermodynamic equilibrium constants were calculated at the 0.95 confidence level as log K (1) o = 4.12 ± 0.47; = ?0.97 ± 0.16 at 250°C. It was shown that Gd3+ undergoes hydrolysis in solutions with pH > 3, and the species Gd(OH) 2 + dominates up to at least pH 5. At pH < 3, Gd occurs in solutions as Gd3+. The second constant of Gd3+ hydrolysis was determined at 250°C as K o = ?5.09 ± 0.5, and the thermodynamic characteristics of the initial Gd2Ti2O7 solid phase were determined: S 298.15 o = 251.4 J/(mol K) and ΔfG 298.15 o = ?3630 ± 10 kJ/mol. 相似文献