首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 484 毫秒
1.
A new mineral eurekadumpite found at the Centennial Eureka Mine in the Tintic district of Juab County in Utah in the United States occurs in the oxidation zone along with quartz, macalpineite, malachite, Zn-bearing olivenite, goethite, and Mn oxides. Eurekadumpite forms spherulites or rosettes up to 1 mm in size and their clusters and crusts up to 1.5 cm2 in cavities. Its individuals are divergent and extremely thin (up to 0.5 mm across and less than 1 μm thick) hexagonal or roundish leaflets. The mineral is deep blue-green or turquoise-colored. Its streaks are light turquoise-colored. Its luster is satiny in aggregates and pearly on individual flakes. Its cleavage is (010) perfect and micalike. Its flakes are flexible but inelastic. Its Mohs hardness is 2.5–3.0, and D(meas) = 3.76(2) and D(calc) = 3.826 g/cm3. The mineral is optically biaxial negative, and α = 1.69(1), β ∼ γ = 1.775(5), and 2V meas = 10(5)°. Its pleochroism is strong: Y = Z = deep blue-green, and X = light turquoise-colored. Its orientation is X = b. The wavenumbers of the bands in the IR spectrum (cm−1; the strong lines are underlined, and w denotes the weak bands) are 3400, 2990, 1980w, 1628, 1373w, 1077, 1010, 860, 825, 803, 721w, 668, 622, 528, 461. The IR spectrum shows the occurrence of the tellurite (Te4+,O3)2− and arsenate (As5+,O4)3− anionic groups and H2O molecules; Cu and Zn cations are combined with OH− groups. The chemical composition of eurekadumpite is as follows (wt %, average of 14 electron-microprobe analyses; H2O determined using the Alimarin method): 0.04 FeO, 36.07 CuO, 20.92 ZnO, 14.02 TeO2, 14.97 As2O5, 1.45 Cl, 13.1 H2O, O = Cl2 −0.33, total 100.24. The empirical formula based on 2 Te atoms is (Cu10.32Zn5.85Fe0.01)Σ16.18(TeO3)2(AsO4)2.97[Cl0.93(OH)0.07]Σ1(OH)18.45 · 7.29H2O. The idealized formula is (Cu,Zn)16(TeO3)2(AsO4)3Cl(OH)18 · 7H2O. Eurekadumpite is monoclinic (pseudohexagonal), and the most probable space groups are P2/m, P2, or Pm. The unit-cell parameters refined from the powder X-ray data are as follows: a = 8.28(3), b = 18.97(2), c = 7.38(2) ?, β = 121.3(6)°, V = 990(6) ?3, and Z = 1. The strongest reflections of the X-ray powder pattern (d, ? (I) [hkl]) are as follows: 18.92(100) [010], 9.45(19) [020], 4.111(13) [[`2]\bar 2 01], 3.777(24) [050, [`2]\bar 2 21, 041], 2.692(15) [[`3]\bar 3 11, 151, [`3]\bar 3 02], 2.524(41)[170, [`2]\bar 2 52, [`1]\bar 1 71], 1.558(22) [[`4]\bar 4 82, [`3]\bar 3 .10.1, 024]. The name of the mineral means, firstly, that it was found in specimens from dumps of the Centennial Eureka Mine. In addition, it could mean found in a dump (the Greek word eureka means I have found it). There is an allusion to the great role that dumps of abandoned mines have played in the discovery of new minerals. Type specimens are deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow, at the Smithsonian National Museum of Natural History in Washington, and at the American Museum of Natural History in New York.  相似文献   

2.
Biachellaite, a new mineral species of the cancrinite group, has been found in a volcanic ejecta in the Biachella Valley, Sacrofano Caldera, Latium region, Italy, as colorless isometric hexagonal bipyramidal-pinacoidal crystals up to 1 cm in size overgrowing the walls of cavities in a rock sample composed of sanidine, diopside, andradite, leucite and hauyne. The mineral is brittle, with perfect cleavage parallel to {10$ \bar 1 $ \bar 1 0} and imperfect cleavage or parting (?) parallel to {0001}. The Mohs hardness is 5. Dmeas = 2.51(1) g/cm3 (by equilibration with heavy liquids). The densities calculated from single-crystal X-ray data and from X-ray powder data are 2.515 g/cm3 and 2.520 g/cm3, respectively. The IR spectrum demonstrates the presence of SO42−, H2O, and absence of CO32−. Biachellaite is uniaxial, positive, ω = 1.512(1), ɛ = 1.514(1). The weight loss on ignition (vacuum, 800°C, 1 h) is 1.6(1)%. The chemical composition determined by electron microprobe is as follows, wt %: 10.06 Na2O, 5.85 K2O, 12.13 CaO, 26.17 Al2O3, 31.46 SiO2, 12.71 SO3, 0.45 Cl, 1.6 H2O (by TG data), −0.10 −O=Cl2, total is 100.33. The empirical formula (Z = 15) is (Na3.76Ca2.50K1.44)Σ7.70(Si6.06Al5.94O24)(SO4)1.84Cl0.15(OH)0.43 · 0.81H2O. The simplified formula is as follows: (Na,Ca,K)8(Si6Al6O24)(SO4)2(OH)0.5 · H2O. Biachellaite is trigonal, space group P3, a =12.913(1), c = 79.605(5) ?; V = 11495(1) ?3. The crystal structure of biachellaite is characterized by the 30-layer stacking sequence (ABCABCACACBACBACBCACBACBACBABC)∞. The tetrahedral framework contains three types of channels composed of cages of four varieties: cancrinite, sodalite, bystrite (losod) and liottite. The strongest lines of the X-ray powder diffraction pattern [d, ? (I, %) (hkl)] are as follows: 11.07 (19) (100, 101), 6.45 (18) (110, 111), 3.720 (100) (2.1.10, 300, 301, 2.0.16, 302), 3.576 (18) (1.0.21, 2.0.17, 306), 3.300 (47) (1.0.23, 2.1.15), 3.220 (16) (2.1.16, 222). The type material of biachellaite has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, registration number 3642/1.  相似文献   

3.
This work reports the synthesis of ferri-clinoholmquistite, nominally Li2(Mg3Fe3+2)Si8O22(OH)2, at varying fO2 conditions. Amphibole compositions were characterized by X-ray (powder and single-crystal) diffraction, microchemical (EMPA) and spectroscopic (FTIR, Mössbauer and Raman) techniques. Under reducing conditions ( NNO+1, where NNO = Nickel–Nickel oxide buffer), the amphibole yield is very high (>90%), but its composition, and in particular the FeO/Fe2O3 ratio, departs significantly from the nominal one. Under oxidizing conditions ( NNO+1.5), the amphibole yield is much lower (<60%, with Li-pyroxene abundant), but its composition is close to the ideal stoichiometry. The exchange vector of relevance for the studied system is M2(Mg,Fe2+) M4(Mg,Fe2+) M2Fe3+–1 M4Li–1, which is still rather unexplored in natural systems. Amphibole crystals of suitable size for structure refinement were obtained only at 800 °C, 0.4 GPa and NNO conditions (sample 152), and have C2/m symmetry. The X-ray powder patterns for all other samples were indexed in the same symmetry; the amphibole closest to ideal composition has a = 9.428(1) Å, b = 17.878(3) Å, c = 5.282(1) Å, = 102.06(2)°, V = 870.8(3) Å3. Mössbauer spectra show that Fe3+ is strongly ordered at M2 in all samples, whereas Fe2+ is disordered over the B and C sites. FTIR analysis shows that the amount of CFe2+ increases for increasingly reducing conditions. FTIR data also provide strong evidence for slight but significant amounts of Li at the A sites.  相似文献   

4.
根据X射线衍射(XRD)分析发现: A Fe3(SO4)2(OH)6(A=K+、H3O+)系列铁钒的XRD数据十分相近,难以用XRD区别,需通过能谱(EDS)辅助分析,才能区分此类铁矾。另外,此类铁矾的003和107面网间距d随K+含量增大而增大,且呈一元三次方程的关系;而033和220面网间距d随K+含量增大而减小,呈一元二次方程的关系。对该现象从铁矾晶体结构方面进行解释:K+、H3O+离子位于较大空隙中,且沿着Z轴方向排列,当K+、H3O+离子之间相互替换时,会导致该铁矾晶体结构在Z轴方向有较明显的变化。  相似文献   

5.
  相似文献   

6.
This paper presents data on burovaite-Ca, the first Ti-dominant member of the labuntsovite group with a calcium D-octahedron. The idealized formula of burovaite-Ca is (K,Na)4Ca2(Ti,Nb)8[Si4O12]4(OH,O)8 · 12H2O. The mineral has been found in the hydrothermal zone of aegirine-microcline pegmatite located in khibinite at Mt. Khibinpakhkchorr, the Khibiny pluton, Kola Peninsula, Russia. Radiaxial intergrowths of burovaite-Ca and labuntsovite-Mn associated with lemmleynite-Ba, analcime, and apophyllite have been identified in caverns within microcline. The mean composition of the mineral is as follows, wt %: 3.72 Na2O, 2.76 K2O, 4.22 CaO, 0.47 SrO, 0.23 BaO, 0.01 MnO, 0.30 Fe2O3, 0.14 Al2O3, 42.02 SiO2, 17.30 TiO2, 15.21 Nb2O5, 12.60 H2O (measured); the total is 98.98. Its empirical formula has been calculated on the basis of [(Si,Al)16O48]: {(Na3.10K1.07Ca0.37Sr0.04Ba0.04)4.62}(Ca1.28Zn0.01)1.29(Ti4.97Nb2.56Fe0.08Ta0.02)7.63(Si15.93Al0.07)16O48(OH6.70O0.93)7.63 · 12H2O. The strongest lines in the X-ray powder diffraction pattern of burovaite-Ca (I-d ?] are as follows: 70–7.08, 40–6.39, 40–4.97, 30–3.92, 40–3.57, 100–3.25, 70–3.11, 50–2.61, 70–2.49, 40–2.15, 50–2.05, 70–1.712, 70–1.577, and 70–1.444. The structure of burovaite-Ca was solved by A.A. Zolotarev, Jr. The mineral is monoclinic, space group C2/m. The unit-cell dimensions are a = 14.529(3), b = 14.203(3), c = 7.899(1), β = 117.37(1)°, V = 1447.57 ?3. Burovaite-Ca is an isostructural Ti-dominant analogue of karupm?llerite-Ca and gjerdingenite-Ca. Two stages of mineral formation—pegmatite proper and hydrothermal—have been recognized in the host pegmatite. The hydrothermal stage included K-Ba-Na, Na-K-Ca, and Na-Sr substages. Burovaite-Ca is related to the intermediate Na-K-Ca substage. At the first substage, labuntsovite-Mn and lemmleynite-Ba were formed, and tsepinite-Na, paratsepinite-Nd, and tsepinite-Sr were formed at the final substage. Thus, the sequence of crystallization of labuntsovite-group minerals is characterized by the replacement of the potassium regime by the sodium regime of alkaline solutions in the evolved host pegmatite.  相似文献   

7.
Florencite-(Sm), a new mineral species of the florencite subgroup, was found in association with xenotime-(Y) in quartz veins of the Maldynyrd Range of the Subpolar Urals as thin zones within rhombohedral crystals of florencite-(Ce) with faceting by { 01[`1]1}\{ 01\bar 11\} and { 10[`1]2}\{ 10\bar 12\} . The thickness of particular florencite-(Sm) zones is 0.01–0.1 mm, and the total thickness of a series of such zones is 1–3 mm. Florencite-(Sm) is colorless and pale pink or pale yellow with white streaks; its Mohs hardness is 5.5–6.0. Its measured and calculated densities are 3.70 and 3.743 g/cm3, respectively. The mineral is transparent, nonpleochroic, and uniaxial (positive), and ω = 1.704(2) and ɛ = 1.713(2). The electron beam’s fluorescence spectrum was 592 nm (intense green luminescence of Sm3+) and 558 nm (yellow luminescence of Nd3+). The chemical composition was as follows (microprobe, average of 2 WDS, wt %): 0.62 La2O3, 3.29 Ce2O3, 1.05 Pr2O3, 10.31 Nd2O3, 12.62 Sm2O3, 0.41 Eu2O3, 2.30 Gd2O3, 0.13 Dy2O3, 0.71 SrO, 0.35 CaO, 29.89 Al2O3, 26.14 P2O5, 0.85 SO3, 0.09 SiO2, 88.76 in total; 10.74 H2O (meas.). The empirical formula based on 14 oxygen atoms is (Sm0.38Nd0.32Gd0.07Ce0.10Pr0.03La0.02Eu0.01Sr0.04Ca0.03)1.0Al3.04(P1.91S0.05Si0.01)1.97O14H5.92. The idealized formula is (Sm,Nd)Al3(PO4)2(OH)6. Mineral is trigonal, space group R3m, a = 6.972(4), c = 16.182(7) ?, V = 681.2 ?3, Z = 3. The XRD pattern is as follows: dln (I) (hkl): 2.925 (10) (113), 1.881 (6) (303), 2.161 (5) (107), 5.65 (4) (101), and 3.479 (4) (110). The IR spectrum: 466, 510, 621, 1036, 1105, 1223, 2957, and 3374 cm−1.  相似文献   

8.
New minerals, shlykovite and cryptophyllite, hydrous Ca and K phyllosilicates, have been identified in hyperalkaline pegmatite at Mount Rasvumchorr, Khibiny alkaline pluton, Kola Peninsula, Russia. They are the products of low-temperature hydrothermal activity and are associated with aegirine, potassium feldspar, nepheline, lamprophyllite, eudialyte, lomonosovite, lovozerite, tisinalite, shcherbakovite, shafranovskite, ershovite, and megacyclite. Shlykovite occurs as lamellae up to 0.02 × 0.02 × 0.5 mm in size or fibers up to 0.5 mm in length usually combined in aggregates up to 3 mm in size, crusts, and parallel-columnar veinlets. Cryptophyllite occurs as lamellae up to 0.02 × 0.1 × 0.2 mm in size intergrown with shlykovite being oriented parallel to {001} or chaotically arranged. Separate crystals of the new minerals are transparent and colorless; the aggregates are beige, brownish, light cream, and pale yellowish-grayish. The cleavage is parallel to (001) perfect. The Mohs hardness of shlykovite is 2.5–3. The calculated densities of shlykovite and cryptophyllite are 2.444 and 2.185 g/cm3, respectively. Both minerals are biaxial; shlykovite: 2V meas = −60(20)°; cryptophyllite: 2V meas > 70°. The refractive indices are: shlykovite: α = 1.500(3), β = 1.509(2), γ = 1.515(2); cryptophyllite: α = 1.520(2), β = 1.523(2), γ = 1.527(2). The chemical composition of shlykovite determined by an electron microprobe (H2O determined from total deficiency) is as follows, wt %: 0.68 Na2O, 11.03 K2O, 13.70 CaO, 59.86 SiO2, 14.73 H2O; the total is 100.00. The empirical formula calculated on the basis of 13 O atoms (OH/H2O calculated from the charge balance) is (K0.96Na0.09)Σ1.05Ca1.00Si4.07O9.32(OH)0.68 · 3H2O. The idealized formula is KCa[Si4O9(OH)] · 3H2O. The chemical composition of cryptophyllite determined by an electron microprobe (H2O determined from the total deficiency) is as follows, wt %: 1.12 Na2O, 17.73 K2O, 11.59 CaO, 0.08 Al2O3, 50.24 SiO2, 19.24 H2O, the total is 100.00. The empirical formula calculated on the basis of (Si,Al)4(O,OH)10 (OH/H2O calculated from the charge balance) is (K1.80Na0.17)Σ1.97Ca0.99Al0.01Si3.99O9.94(OH)0.06 · 5.07H2O. The idealized formula is K2Ca[Si4O10] · 5H2O. The crystal structures of both minerals were solved on single crystals using synchrotron radiation. Shlykovite is monoclinic; the space group is P21/n; a = 6.4897(4), b = 6.9969(5), c = 26.714(2)?, β = 94.597(8)°, V = 1209.12(15)?3, Z = 4. Cryptophyllite is monoclinic; the space group is P21/n; a = 6.4934(14), b = 6.9919(5), c = 32.087(3)?, β = 94.680(12)°, V= 1451.9(4)?, Z = 4. The strongest lines of the X-ray powder patterns (d, ?-I, [hkl] are: shlykovite 13.33–100[002], 6.67–76[004], 6.47–55[100], 3.469–45[021], 3.068–57[$ \bar 1 $ \bar 1 21], 3.042–45[121], 2.945–62[ 23], 2.912–90[025, 12, 211]; cryptophyllite 16.01–100[002], 7.98–24[004], 6.24–48[101], 3.228–22[$ \bar 1 $ \bar 1 09], 3.197–27[0.0.10], 2.995–47[122], 2.903–84[123, 204, $ \bar 1 $ \bar 1 24, 211], 2.623–20[028, 08, 126]. Shlykovite and cryptophyllite are members of new related structural types. Their structures are based on a two-layer packet consisting of tetrahedral Si layers linked with octahedral Ca chains. Mountainite, shlykovite and cryptophyllite could be combined into the mountainite structural family. Shlykovite is named in memory of Russian geologist V. G. Shlykov (1941–2007); the name cryptophyllite is from the Greek words meaning concealed and leaf that allude to its layered structure (phyllosilicate) in combination with a lamellar habit and intimate intergrowths with visually indistinguishable shlykovite. Type specimens of the minerals are deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow.  相似文献   

9.
The 10?-phase, Mg3Si4O10(OH)2 · nH2O, where n = 0.65÷2, belongs to the group of dense hydrous magnesium silicates (DHMS), which were produced in experiments and are regarded as hypothetical mineral carriers for H2O in the mantle. However, DHMS were almost never observed in nature. The only exception is the finding of the 10?-phase as nanoinclusions in olivines from mantle nodules in kimberlites. The inclusions with sizes of a few ten nanometers have a pseudohexagonal habit and are characterized by the presence of voids free of solids. The 10?-phase fills the equatorial parts of the inclusions, and, in the majority of inclusions, it is replaced by the low-pressure serpentine + talc assemblage. Based on the analysis of electron microscope images, a model was proposed for the solid-state formation of inclusions, the precursory material of which was transformed to the 10?-phase with the liberation of a water fluid. According to this model, the formation of hydrous nanoinclusions and their subsequent autoserpentinization occurred without the influx of H2O from the external medium through the mobilization of intrinsic hydroxyl-bearing point defects trapped during olivine crystallization. The subsequent autoserpentinization of the inclusions occurred during decompression owing to interaction between the inclusion material and the host olivine matrix. The process was accompanied by the partial exhaustion of the fluid phase and the replacement 10?-phase + H2O = Serp + Tc. The criterion for the credibility of the model is the conservation of the volume of material during the reaction at P = const and T = const. Original Russian Text ? N.R. Khisina, R. Wirth, 2008, published in Geokhimiya, 2008, No. 4, pp. 355–363.  相似文献   

10.
Alloriite, a new mineral species, has been found in volcanic ejecta at Mt. Cavalluccio (Campagnano municipality, Roma province, Latium region, Italy) together with sanidine, biotite, andradite, and apatite. The mineral is named in honor of Roberto Allori (b. 1933), an amateur mineralogist and prominent mineral collector who carried out extensive and detailed field mineralogical investigations of volcanoes in the Latium region. Alloriite occurs as short prismatic and tabular crystals up to 1.5 × 2 mm in size. The mineral is colorless, transparent, with a white streak and vitreous luster. Alloriite is not fluorescent and brittle; the Mohs’ hardness is 5. The cleavage is imperfect parallel to {10 0}. The density measured with equilibration in heavy liquids is 2.35g/cm3 and calculated density (D calc) is 2.358 g/cm3 (on the basis of X-ray single-crystal data) and 2.333 g/cm3 (from X-ray powder data). Alloriite is optically uniaxial, positive, ω = 1.497(2), and ɛ = 1.499(2). The infrared spectrum is given. The chemical composition (electron microprobe, H2O determined using the Penfield method, CO2, with selective sorption, wt %) is: 13.55 Na2O, 6.67 K2O, 6.23 CaO, 26.45 Al2O3, 34.64 SiO2, 8.92 SO3, 0.37 Cl, 2.1 H2O, 0.7 CO2, 0.08-O = Cl2, where the total is 99.55. The empirical formula (Z = 1) is Na19.16K6.21Ca4.87(Si25.26Al22.74O96)(SO4)4.88(CO3)0.70Cl0.46(OH)0.76 · 4.73H2O. The simplified formula (taking into account the structural data, Z = 4) is: [Na(H2O)][Na4K1.5(SO4)] · [Ca(OH,Cl)0.5](Si6Al6O24). The crystal structure has been studied (R = 0.052). Alloriite is trigonal, the space group is P31c; the unit-cell dimensions are a = 12.892(3), c = 21.340(5) ?, and V = 3071.6(15) ?3. The crystal structure of alloriite is based on the same tetrahedral framework as that of afghanite. In contrast to afghanite containing clusters [Ca-Cl]+ and chains ...Ca-Cl-Ca-Cl..., the new mineral contains clusters [Na-H2O]+ and chains ...Na-H2O-Na-H2O.... The strongest reflections in the X-ray powder diffraction pattern [d, ? (I, %)(hkl)] are: 11.3(70)(100), 4.85(90)(104), 3.76(80)(300), 3.68(70)(301), 3.33(100)(214), and 2.694(70)(314, 008). The type material of alloriite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. The registration number is 3459/1. Original Russian Text ? N.V. Chukanov, R.K. Rastsvetaeva, I.V. Pekov, A.E. Zadov, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, No. 1, pp. 82–89. A new mineral alloriite and its name were accepted by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, May 8, 2006. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, August 2, 2006.  相似文献   

11.
A new heterophyllosilicate mineral schüllerite was found in the L?hley basalt quarry in the Eifel volcanic region, Germany, as a member of the late mineral assemblage comprising nepheline, leucite, augite, phlogopite, magnetite, titanite, fresnoite, barytolamprophyllite, fluorapatite, perovskite, and pyrochlore. Flattened brown crystals of schüllerite up to 0.5 × 1 × 2 mm in size and their aggregates occur in miarolic cavities of alkali basalt. The mineral is brittle, with a Mohs hardness 3–4 and perfect cleavage parallel to (001). D calc = 3.974 g/cm3. Its IR spectrum is individual and does not contain bands of OH−, CO32− or H2O. Schüllerite is biaxial (−), α = 1.756(3), β = 1.773(4), γ = 1.780(4), 2V meas = 40(20)°. Dispersion is weak, r < ν. Pleochroism is medium X > Y > Z, brown to dark brown. Chemical composition (electron microprobe, mean of five-point analyses, Fe2+/Fe3+ ratio determined by the X-ray emission spectroscopic data, wt %): 3.55 Na2O, 0.55 K2O, 3.89 MgO, 2.62 CaO, 1.99 ArO, 28.09 BaO, 3.43 FeO, 8.89 Fe2O3, 1.33 Al2O3, 11.17 TiO2, 2.45 Nb2O5, 26.12 SiO2, 2.12 F, −0.89 -O=F2, 98.98 in total. The empirical formula is (Ba1.68Sr0.18K0.11Na1.05Ca0.43Mn0.47Mg0.88Fe0.442+Fe1.023+Ti1.28Nb0.17Al0.24)Σ7.95Si3.98O16.98F1.02. The crystal structure was refined on a single crystal. Schüllerite is triclinic, space group P1, unit cell parameters: a = 5.4027(1), b = 7.066(4), c = 10.2178(1)?, α = 99.816(1), β = 99.624(1), γ = 90.084(1)°, V = 378.75(2) ?3, Z = 1. The strongest lines of the X-ray powder diffraction pattern [d, ?, (I, %)]: 9.96(29), 3.308(45), 3.203(29), 2.867(29), 2.791(100), 2.664(46), 2.609(36), 2.144(52). The mineral was named in honor of Willi Schüller (born 1953), an enthusiastic, prominent amateur mineral collector, and a specialist in the mineralogy of Eifel. Type specimens have been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, registration no. 3995/1,2.  相似文献   

12.
  相似文献   

13.
Pyrope-knorringite garnets, Mg3(Al1-X Cr3+X)2Si3O12 with X=0.25, 0.50, and 1.00, were synthesized between 9 and 16 GPa and 1300 and 1600 °C, using multianvil high-pressure techniques. The garnets with X=0.25 and 0.50 are fine-grained, pink and violet in color. The end-member knorringites with X=1.00 are black when compact and gray when coarse-grained. The fine powder is greenish gray in natural light and pale pink under a tungsten lamp. Powder remission spectra in the wavenumber range 30 000–10 000 cm–1 on finely powdered crystals were measured by two different methods: (I.) by the use of a small integrating sphere for small samples or (II.) microscope-spectrometric measurement using diffusely reflected radiation from a 45° illuminated microsample. Both methods yielded similar diffuse reflectance spectra. The following crystal-field parameters of [6]Cr3+ were determined for garnets with X=0.25, 0.50, 1.00: 10 Dq=17 856, 17 596, 17 286 cm–1; and B=654, 677, 706 cm–1; nephelauxetic ratio =(Bfield/Bfree)= 0.71, 0.74, 0.77. The -values indicate decreasing covalency of the Cr–O bond with increasing Cr content. The 10 Dq value for together with the mean Cr–O distance in end-member knorringite, 1.96 Å (Novak and Gibbs 1971), were used to calculate from the spectral data, local mean Cr–O distances (Langer 2001a) as a function of composition. The results indicate relatively strong local site relaxation with a value of =0.77.  相似文献   

14.
The sediments in the Salford Quays, a heavily-modified urban water body, contain high levels of organic matter, Fe, Zn and nutrients as a result of past contaminant inputs. Vivianite [Fe3(PO4)2 · 8H2O] has been observed to have precipitated within these sediments during early diagenesis as a result of the release of Fe and P to porewaters. These mineral grains are small (<100 μm) and micron-scale analysis techniques (SEM, electron microprobe, μ-EXAFS, μ-XANES and Raman) have been applied in this study to obtain information upon the structure of this vivianite and the nature of Zn uptake in the mineral. Petrographic observations, and elemental, X-ray diffraction and Raman spectroscopic analysis confirms the presence of vivianite. EXAFS model fitting of the FeK-edge spectra for individual vivianite grains produces Fe–O and Fe–P co-ordination numbers and bond lengths consistent with previous structural studies of vivianite (4O atoms at 1.99–2.05 Å; 2P atoms at 3.17–3.25 Å). One analysed grain displays evidence of a significant Fe3+ component, which is interpreted to have resulted from oxidation during sample handling and/or analysis. EXAFS modelling of the Zn K-edge data, together with linear combination XANES fitting of model compounds, indicates that Zn may be incorporated into the crystal structure of vivianite (4O atoms at 1.97 Å; 2P atoms at 3.17 Å). Low levels of Zn sulphate or Zn-sorbed goethite are also indicated from linear combination XANES fitting and to a limited extent, the EXAFS fitting, the origin of which may either be an oxidation artifact or the inclusion of Zn sulphate into the vivianite grains during precipitation. This study confirms that early diagenetic vivianite may act as a sink for Zn, and potentially other contaminants (e.g. As) during its formation and, therefore, forms an important component of metal cycling in contaminated sediments and waters. Furthermore, for the case of Zn, the EXAFS fits for Zn phosphate suggest this uptake is structural and not via surface adsorption.  相似文献   

15.
A new mineral fivegite has been identified in a high-potassium hyperalkaline pegmatite at Mt. Rasvumchorr in the Khibiny alkaline complex of the Kola Peninsula in Russia. This mineral is a product of the hydrothermal alteration of delhayelite (homoaxial pseudomorphs after its crystals up to 2 × 3 × 10 cm in size). Hydrodelhayelite, pectolite, and kalborsite are products of fivegite alteration. The associated minerals are aegirine, potassic feldspar, nepheline, sodalite, magnesiumastrophyllite, lamprophyllite, lomonosovite, shcherbakovite, natisite, lovozerite, tisinalite, ershovite, megacyclite, shlykovite, cryptophyllite, etc. Areas of pure unaltered fivegite are up to 2 mm in width. The mineral is transparent and colorless; its luster is vitreous to pearly. Its Cleavage is perfect (100) and distinct (010). Its Mohs hardness is 4, D(meas) = 2.42(2), and D(calc) = 2.449 g/cm3. Fivegite is optically biaxial positive: α 1.540(1), β 1.542(2), γ 1.544(2), and 2V(meas) 60(10)°. Its orientation is X = a, y = c, and Z = b. Its IR spectrum is given. Its chemical composition (wt %; electron microprobe, H2O determined by selective sorption) is as follows: 1.44 Na2O, 19.56 K2O, 14.01 CaO, 0.13 SrO, 0.03 MnO, 0.14 Fe2O3, 6.12 Al2O3, 50.68 SiO2, 0.15 SO3, 0.14 F, 3.52 Cl, 4.59 H2O; −O = −0.85(Cl,F)2; total 99.66. The empirical formula based on (Si + Al + Fe) = 8 is H4.22K3.44Na0.39Ca2.07Sr0.01Fe0.01Al1.00Si6.99O21.15F0.06Cl0.82(SO4)0.02. The simplified formula is K4Ca2[AlSi7O17(O2 − x OH x ][(H2O)2 − x OH x ]Cl (X = 0−2). Fivegite is orthorhombic: Pm21 n, a = 24.335(2), b = 7.0375(5), c = 6.5400(6) ?, V = 1120.0(2) ?3, and Z = 2. The strongest reflections of the X-ray powder pattern are as follows (d, ?, (I, %), [hkl]): 3.517(38) [020], 3.239(28) [102], 3.072(100) [121, 701], 3.040(46) [420, 800, 302], 2.943 (47) [112], 2.983(53) [121], 2.880 (24) [212, 402], 1.759(30) [040, 12.2.0]. The crystal structure was studied using a single crystal: R hkl = 0.0585. The base of fivegite structure is delhayelite-like two-layer terahedral blocks [(Al,Si)4Si12O34(O4 − x OH x )] linked by Ca octahedral chains. K+ and Cl− are localized in zeolite-like channels within the terahedral blocks, whereas H2O and OH occur between the blocks. The mineral is named in memory of the Russian geological and mining engineer Mikhail Pavlovich Fiveg (1899–1986), the pioneering explorer of the Khibiny apatite deposits. The type specimen is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow. The series of transformations is discussed: delhayelite K4Na2Ca2[AlSi7O19]F2Cl—fivegite K4Ca2[AlSi7O17(O2 − x OH x ]Cl—hydrodelhayelite KCa2[AlSi7O17(OH)2](H2O)6 − x .  相似文献   

16.
The 1986 lethal eruption of Lake Nyos (Cameroon) was caused by a sudden inversion between deep, CO2-loaded bottom lake waters and denser, gas-free surface waters. A deep CO2 source has been found in fluid inclusions which occur predominantly in clinopyroxenes from lherzolitic mantle xenoliths, brought to the surface by the last erupted alkali basalts. P–T conditions of CO2 trapping correspond to a gas density equal (or higher) than that of liquid water. It is suggested that this dense CO2, found in many ultrabasic mantle xenoliths worldwide, has accumulated at km depth, below a column of descending lake water. It may remain in a stable state for a long period, as long as the temperature is above the density inversion temperature for pure H2O/CO2 systems. At an estimated depth of about 3 km, cooling by descending waters (to about 30 °C) induces a density inversion for the upper part of the CO2 reservoir. This causes a constant, regular upstream of low-density CO2 which, in its turn, feeds the shallower lake density inversion.  相似文献   

17.
1974年在一水晶矿石英脉晶洞中,发现了一种含Ba、Li的硅酸盐新矿物--纤钡锂石。我们对纤钡锂石进行了光性研究、比重测定、差热及热失重分析、红外光谱分析、X射线单晶结构分析等工作,现分述如下。  相似文献   

18.
通过密度泛函理论模拟了H_2O_2和SO_2气体在矿物氧化物(α-Fe_2O_3)表面上的非均相反应,研究了H_2O_2和SO_2在α-Fe_2O_3(001)表面的吸附机制和氧化机制。研究结果表明,SO_2、H_2O_2均在α-Fe_2O_3(001)表面通过Fe原子进行吸附,H_2O_2相比于SO_2优先吸附在α-Fe_2O_3(001)表面,且H_2O_2在表面的赋存形式趋向于两个·OH形式吸附。通过二者共吸附的局域态密度、差分电荷密度、Mulliken电荷布局分析结果发现,SO_2和H_2O_2的共吸附形式是通过H_2O_2产生的·OH吸附在α-Fe_2O_3(001)表面,同时SO_2被H_2O_2产生的·OH氧化[S(SO_2)-电荷布局:0. 79 e→1. 32 e; O(H_2O_2)-电荷布局:-0. 77 e→-1. 11 e]形成·OH+SO_2团簇。模拟结果表明大气微量气体H_2O_2能够在矿物氧化物表面介导SO_2吸附并促进SO_2的转化,为理解H_2O_2在大气中非均相氧化SO_2的反应过程提供了理论依据。  相似文献   

19.
Enthalpies of formation of ferrihydrite and schwertmannite were measured by acid solution calorimetry in 5 N HCl at 298 K. The published thermodynamic data for these two phases and ε-Fe2O3 were evaluated, and the best thermodynamic data for the studied compounds were selected.Ferrihydrite is metastable in enthalpy with respect to α-Fe2O3 and liquid water by 11.5 to 14.7 kJ•mol−1 at 298.15 K. The less positive enthalpy corresponds to 6-line ferrihydrite, and the higher one, indicating lesser stability, to 2-line ferrihydrite. In other words, ferrihydrite samples become more stable with increasing crystallinity. The best thermodynamic data set for ferrihydrite of composition Fe(OH)3 was selected by using the measured enthalpies and (1) requiring ferrihydrite to be metastable with respect to fine-grained lepidocrocite; (2) requiring ferrihydrite to have entropy higher than the entropy of hypothetical, well-crystalline Fe(OH)3; and (3) considering published estimates of solubility products of ferrihydrite. The ΔG°f for 2-line ferrihydrite is best described by a range of −708.5±2.0 to −705.2±2.0 kJ•mol−1, and ΔG°f for 6-line ferrihydrite by −711.0±2.0 to −708.5±2.0 kJ•mol−1.A published enthalpy measurement by acid calorimetry of ε-Fe2O3 was re-evaluated, arriving at ΔH°f (ε-Fe2O3) = −798.0±6.6 kJ•mol−1. The standard entropy (S°) of ε-Fe2O3 was considered to be equal to S° (γ-Fe2O3) (93.0±0.2 J•K−1•mol−1), giving ΔG°f (ε-Fe2O3) = −717.8±6.6 kJ•mol−1. ε-Fe2O3 thus appears to have no stability field, and it is metastable with respect to most phases in the Fe2O3-H2O system which is probably the reason why this phase is rare in nature.Enthalpies of formation of two schwertmannite samples are: ΔH°f (FeO(OH)0.686(SO4)0.157•0.972H2O) = −884.0±1.3 kJ•mol−1, ΔH°f (FeO(OH)0.664(SO4)0.168•1.226H2O) = −960.7±1.2 kJ•mol−1. When combined with an entropy estimate, these data give Gibbs free energies of formation of −761.3 ± 1.3 and −823.3 ± 1.2 kJ•mol−1 for the two samples, respectively. These ΔGf° values imply that schwertmannite is thermodynamically favored over ferrihydrite over a wide range of pH (2-8) when the system contains even small concentration of sulfate. The stability relations of the two investigated samples can be replicated by schwertmannite of the “ideal” composition FeO(OH)3/4(SO4)1/8 with ΔG°f = −518.0±2.0 kJ•mol−1.  相似文献   

20.
纤钡锂石产于湖南临武香花岭地区一水晶矿锂云母石英脉晶洞中,与锂云母、石英等矿物共生。矿物为浅黄白色,丝绢光泽,呈针状、纤维状、放射状或平行束状集合体,纤维长达1厘米。经X射线单晶及粉晶衍射测定:该矿物属斜方晶系,空间群Ccca,晶胞参数:a=13.60(?),b=20.24(?),e=5.16(?)。最强衍射线为:10.12(?)(100) 4.05(?)(78) 3.39(?)(91) 2.605(?)(31)2.390(?)(28)。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号