Electron paramagnetic resonance and ENDOR studies of Cr3+ - Al3+ pairs in forsterite     

L. V. Bershov  J.-M. Gaite  S. S. Hafner  H. Rager 《Physics and Chemistry of Minerals》1983,9(3-4):95-101

The electron paramagnetic resonance (EPR) spectrum of Cr³⁺ in synthetic crystals of forsterite consists primarily of lines of Cr³⁺ “isolated” at the M1 and M2 positions in a “perfect” crystal environment without local charge compensation. In addition it shows two nonequivalent superhyperfine-split sextets with different intensities which are due to strong interaction of the Cr³⁺ electron spin S (S=3/2) with an adjacent nuclear spin I(I=5/2). Electron nuclear double resonance (ENDOR) experiments revealed that the sextets result from Cr³⁺ (M1) - Al³⁺ and Cr³⁺ (M2) - Al³⁺ pairs, Al being located at adjacent tetrahedral Si sites. The g, D, A, and A′ tensor components of the Cr³⁺ - Al³⁺ pairs have been determined at room temperature. The values of the pairs are distinct although they are not very different from the corresponding data of “isolated” Cr³⁺. From the intensities of the EPR spectra the relative concentration of the Cr³⁺ - Al³⁺ pairs with respect to “isolated” Cr³⁺ has been estimated.  相似文献   

EPR study of chromium-doped forsterite crystals: Cr3+(M1) with associated trivalent ions Al3+ and Sc3+     

I. D. Ryabov 《Physics and Chemistry of Minerals》2012,39(9):725-732

Electron paramagnetic resonance (EPR) study of single crystals of forsterite co-doped with chromium and scandium has revealed, apart from the known paramagnetic centers Cr³⁺(M1) and Cr³⁺(M1)– $ V_{{{\text{Mg}}^{2 + } }} $ (M2) (Ryabov in Phys Chem Miner 38:177–184, 2011), a new center Cr³⁺(M1)– $ V_{{{\text{Mg}}^{2 + } }} $ (M2)–Sc³⁺ formed by a Cr³⁺ ion substituting for Mg²⁺ at the M1 structural position with a nearest-neighbor Mg²⁺ vacancy at the M2 position and a Sc³⁺ ion presumably at the nearest-neighbor M1 position. For this center, the conventional zero-field splitting parameters D and E and the principal g values have been determined as follows: D?=?33,172(29) MHz, E?=?8,482(13) MHz, g?=?[1.9808(2), 1.9778(2), 1.9739(2)]. The center has been compared with the known ion pair Cr³⁺(M1)–Al³⁺ (Bershov et al. in Phys Chem Miner 9:95–101, 1983), for which the refined EPR data have been obtained. Based on these data, the known sharp M1″ line at 13,967?cm^?1 (with the splitting of 1.8?cm^?1), observed in low-temperature luminescence spectra of chromium-doped forsterite crystals (Glynn et al. in J Lumin 48, 49:541–544, 1991), has been ascribed to the Cr³⁺(M1)–Al³⁺ center. It has been found that the concentration of the new center increases from 0 up to 4.4?×?10¹⁵?mg^?1, whereas that of the Cr³⁺(M1) and Cr³⁺(M1)– $ V_{{{\text{Mg}}^{2 + } }} $ (M2) centers quickly decreases from 7.4?×?10¹⁵?mg^?1 down to 3?×?10¹⁵?mg^?1 and from 2.7?×?10¹⁵?mg^?1 down to 0.5?×?10¹⁵?mg^?1, i.e., by a factor of 2.5 and 5.4, respectively, with an increase of the Sc content from 0 up to 0.22 wt?% (at the same Cr content 0.25 wt?%) in the melt. When the Sc content exceeds that of Cr, the concentration of the new center decreases most likely due to the formation of the Sc³⁺(M1)– $ V_{{{\text{Mg}}^{2 + } }} $ (M2)–Sc³⁺ complex instead of the Cr³⁺(M1)– $ V_{{{\text{Mg}}^{2 + } }} $ (M2)–Sc³⁺ center. The formation of such ordered neutral complex is in agreement with the experimental results, concerning the incorporation of Sc into olivine, recently obtained by Grant and Wood (Geochim Cosmochim Acta 74:2412–2428, 2010).  相似文献   

The geochemistry of pyroxenes from the lower layered series of the Jimberlana intrusion,Western Australia     

I. H. Campbell  G. D. Borley 《Contributions to Mineralogy and Petrology》1974,47(4):281-297

Most of the Al³⁺ entering the pyroxenes does so by substituting for tetrahedral Si⁴⁺. This creates a charge imbalance that requires the simultaneous entry of Cr³⁺, Ti⁴⁺, Fe³⁺ or Al³⁺ into octahedral sites. Cr³⁺, because of its high crystal field stabilisation energy (CFSE), is the most important of these elements to enter the early-formed pyrosenes but it is replaced by Ti⁴⁺ later in fractionation when the Cr³⁺ content of the melt becomes depleted. The dependence of Cr³⁺ and Ti⁴⁺ on charge balance controls their partition between coexisting pyroxenes and olivines. Ca-rich pyroxene which contains more Al³⁺ than Ca-poor pyroxene also has more Ti⁴⁺ and Cr³⁺ whereas olivine, which contains negligible Al³⁺, has low Cr³⁺ and Ti⁴⁺. The Al³⁺ content of pyroxenes is influenced by changes in P, T, \(a_{{\text{SiO}}_{\text{2}} }\) and \(a_{{\text{Al}}_{\text{2}} {\text{O}}_{\text{3}} }\) of the magma and by the nature of the ion providing charge balance in the octahedral site. Of these \(a_{{\text{SiO}}_{\text{2}} }\) is dominant and variations in the Al³⁺ content of the Jimberlana pyroxenes correspond closely with the expected changes in the \(a_{{\text{SiO}}_{\text{2}} }\) of the melt. The substitution of divalent ions, such as Mn²⁺ and Ni²⁺, in the pyroxene lattice is by replacement of Fe²⁺ or Mg²⁺ in the octahedral M ₃ and M ₂ sites and is therefore independent of charge balance. If there are no size restrictions, the principal factor to be considered is the CFSE the ion receives in octahedral co-ordination. Ni²⁺, which receives a high CFSE, partitions strongly between the early-formed pyroxenes and olivines and therefore becomes depleted in the magma with fractionation. Conversely Mn²⁺, which receives zero CFSE, concentrates in the magma with fractionation and becomes a more important substitute in the later-formed pyroxenes. Its geochemical behaviour is controlled by its size. The narrow miscibility gap of the Jimberlana pyroxenes and the high En content of the Ca-poor pyroxenes at the bronzite pigeonite changeover suggest that these pyroxenes crystallised at a higher temperature than pyroxenes of comparable composition from other intrusions.  相似文献   

Synthetic Mn3+-kyanite and viridine, (Al2-xMn x 3+ ) SiO5, in the system Al2O3-MnO-MnO2-SiO2     

I. Abs-Wurmbach  Prof. Dr. K. Langer 《Contributions to Mineralogy and Petrology》1975,49(1):21-38

Experiments on the join Al₂SiO₅-“Mn₂SiO₅” of the system Al₂O₃-SiO₂-MnO-MnO₂ in the pressure/temperature range 10–20 kb/900–1050° C with gem quality andalusite, Mn₂O₃, and high purity SiO₂ as starting materials and using /_O2-buffer techniques to preserve the Mn³⁺ oxidation state had following results: At 20 kb/1000°C orange-yellow kyanite mixed crystals are formed. The kyanite solid solubility is limited at about (Al_1.88Mn _0.12 ³⁺ )SiO₅ and, thus, equals approximately that on the join Al₂SiO₅-“Fe₂SiO₅” (Langer and Frentrup, 1973) indicating that there is no Jahn-Teller stabilisation of Mn³⁺ in the kyanite matrix. 5 mole % substitution causes the kyanite lattice constants a _o, b _o, c _o, and V _o to increase by 0.015, 0.009, 0.014 Å, and 1.6 ų, resp., while α, β, γ, remain unchanged. Between 10 and 18 kb/900°C, Mn³⁺-substituted, strongly pleochroitic (emeraldgreen-yellow) andalusite_ss (viridine) was obtained. At 15 kb/900°C, the viridine compositional range is about (Al_1.86Mn _0.14 ³⁺ )SiO₅-(Al_1.56Mn _0,44 ³⁺ )SiO₅. Thus, Al→Mn³⁺ substitutional degrees are appreciably higher in andalusite than in kyanite, proving a strong Jahn-Teller effect of Mn³⁺ in the andalusite structure, which stabilises this structure type at the expense of kyanite and sillimanite and, thus, enlarges its PT-stability range extremely. 17 mole % substitution cause the andalusite constants a _o, b _o, c _o, and V _o to increase by 0.118, 0.029, 0.047 Å and 9.4 ų, resp. At “Mn₂SiO₅”-contents smaller than about 7 mole %, viridine coexists with Mn-poor kyanite. At “Mn₂SiO₅”-concentrations higher than the maximum kyanite or viridine miscibility, braunite (tetragonal, ideal formula Mn²⁺Mn³⁺[O₈/Si0₄]), pyrolusite and SiO₂ were found to coexist with the Mn³⁺-saturated ky _ss or and _ss, respectively. In both cases, braunites were Al-substituted (about 1 Al for 1 Mn³⁺). Pure synthetic braunites had the lattice constants a _o 9.425, c _o, 18.700 Å, V _o 1661.1 ų (ideal compn.) and a _o 9.374, c _o 18.593 ų, V _o 1633.6 ų (1 Al for 1 Mn³⁺). Stable coexistence of the Mn²⁺-bearing phase braunite with the Mn⁴⁺-bearing phase pyrolusite was proved by runs in the limiting system MnO-MnO₂-SiO₂.  相似文献   

The Cr<Superscript>6+</Superscript> impurity in supergene oxosalts in chromate mineralization occurrences of the Urals     

D. A. Khanin  I. V. Pekov  A. V. Pakunova  I. A. Ekimenkova  V. O. Yapaskurt 《Moscow University Geology Bulletin》2016,71(5):330-336

Based on the results of more than 600 electron microprobe analyses of 25 minerals the distribution pattern of the Cr⁶⁺ impurity in vanadates, phosphates, and arsenates collected in oxidation zones of six ore deposits of the Urals was studied. Among them are Pb minerals of the brackebuschite, apatite, adelite, and tsumcorite groups and alunite supergroup, as well as carminite, cornwallite, and bayidonite. Vanadates and arsenates with brackebuschite-type structures show a high affinity to Cr⁶⁺. The maximum content of the Cr⁶⁺ impurity is characteristic of minerals with specified Fe³⁺ trivalent cations (ferribushmakinite, arsenbrackebuschite, and gartrellite) or Al³⁺ (plumbogummite and bushmakinite). The prevailing scheme of isomorphous substitution, according to which chromium enters into the compositions of these minerals, is heterovalent: Cr⁶⁺ + M ²⁺ → Т ⁵⁺ + M ³⁺ (where Т = V, As, P; M ³⁺ = Fe, Al; M ²⁺ = Сu, Zn), whereas the role of isovalent substitutions Cr⁶⁺ → S⁶⁺ and Cr⁶⁺ → Mo⁶⁺ in oxosalts that formed in mineral occurrences of the Urals is insignificant.  相似文献   

Electronic absorption spectra of Cr3+ ions in natural clinopyroxenes     

V. M. Khomenko  A. N. Platonov 《Physics and Chemistry of Minerals》1985,11(6):261-265

The polarized (E‖a′, E‖b and E‖c) electronic absorption spectra of five natural chromium-containing clinopyroxenes with compositions close to chromdiopside, omphacite, ureyite-jadeite (12.8% Cr₂O₃), jadeite, and spodumene (hiddenite) were studied. The polarization dependence of the intensities of the Cr³⁺ bands in the clinopyroxene spectra cannot be explained by the selection rules for the point groups C ₂ or C _2v but can be accounted for satisfactorily with the help of the higher order pseudosymmetry model, i.e. with selection rules for the point symmetry group C _3v. The trigonal axis of the pseudosymmetry crystal field forms an angle of 20.5° with the crystallographic direction c in the (010) plane. D _q increases from diopside (1542 cm^?1) through omphacite (1552 cm^?1), jadeite (1574 cm^?1) to spodumene (1592 cm^?1). The parameter B which is a measure of covalency for Cr³⁺-O bonds at M1 sites in clinopyroxene depends on the Cr³⁺ concentration and the cations at M2 sites.  相似文献   

The reaction forsterite+cordierite=aluminous orthopyroxene+spinel in the system MgO-Al2O3-SiO2     

Claude T. Herzberg 《Contributions to Mineralogy and Petrology》1983,84(1):84-90

Reversal experiments at 1,150–1,300°C on the reaction forsterite+cordierite=aluminous orthopyroxene+spinel in the system MgO-Al₂O₃-SiO₂ show the equilibrium to have a negativedT/dP. The slope andT-P location of this equilibrium have been modelled using available heat capacity data and various structural models which explore the configurational entropy contributions to the totalΔS. The experimental data are consistent with the aluminous orthopyroxene model of Ganguly and Ghose (1979) where limited Al disorder occurs between theM1 andM2 sites, Al-Si mixing occurs on the tetrahedralB site with the ‘aluminum avoidance’ principle maintained, and Mg-Al disorder occurs in spinel with an interchange enthalpy of 9–12 kcal mol^?1. Additionally, Al-Si disordering which occurs in the indialite structure of cordierite is inconsistent with the experimental data and all pyroxene and spinel mixing models; consequently, Si and Al in anhydrous cordierites to 1,300°C in the system MgO-Al₂O₃-SiO₂ must be largely ordered.  相似文献   

Kanonaite, (Mn 0.76 3+ Al0.23Fe 0.02 3+ )[6]Al[5][O¦SiO4], a new mineral isotypic with andalusite     

S. Vrána  M. Rieder  J. Podlaha 《Contributions to Mineralogy and Petrology》1978,66(3):325-332

Kanonaite forms rare porphyroblasts up to 12mm long in a gahnite— Mg-chlorite — coronadite — quartz schist occurring near Kanona, Zambia. The composition is (microprobe analysis): SiO₂ 32.2, Al₂O₃ 33.9, Mn as Mn₂O₃ 32.2, Fe₂O₃ 0.66, ZnO 0.13, MgO 0.04, BaO 0.04, TiO₂ 0.01, CaO 0.01, PbO 0.01, CuO 0.01, total 99.21, corresponding to $$\left( {{\text{Mn}}_{{\text{0}}{\text{.76}}}^{{\text{3 + }}} {\text{Al}}_{{\text{0}}{\text{.23}}} {\text{Fe}}_{{\text{0}}{\text{.015}}}^{{\text{3 + }}} } \right)_{1.005}^{\left[ 6 \right]} {\text{AL}}_{1.00}^{\left[ 5 \right]} \left[ {{\text{O}}_{{\text{1}}{\text{.00}}} |{\text{Si}}_{{\text{0}}{\text{.99}}} {\text{O}}_{{\text{4}}{\text{.00}}} } \right]$$ The mineral is greenish black, strongly pleochroic with X(∥a) yellow green, Y(∥b) bluish green, Z(∥c) deep golden yellow, biaxial positive, with 2V = 53°(3°), α = 1.702, β = 1.730, γ = 1.823. Vickers microhardness (100 gram load) ranges between 906 and 1017kp/mm². The structure is orthorhombic, isotypic with andalusite, space group Pnnm, a = 0.7953(2), b = 0.8038(2), c = 0.5619(2) nm, V = 0.3592(1) nm³, a/b = 0.9895(3), c/b = 0.6990(3), S.G.(_x) = 3.395 g/cm³, Z = 4. The strongest X-ray powder lines are (d in nm, I, hkl):0.5669, 100, 110; 0.4590, 75, 011 and 101; 0.3577, 90, 120 and 210; 0.2827, 94, 220; 0.2517, 90, 310 and 112; 0.2212, 83, 320, 122 and 212. Comparison of the intensities of 373 observed X-ray reflections with those calculated for several models of Mn³⁺-distribution indicates octahedral coordination of all or most of the manganese present. Interpretation of magnetic measurements (μ_eff = 3.15B.M. per Mn atom at 25 ° C) indirectly supports octahedral coordination of Mn³⁺. The name of the mineral is for Kanona, a town near the type locality. The name is proposed for the end member Mn^{3+ [6]}Al^[5][O¦SiO₄] and for members of the solid-solution series towards andalusite with octahedral Mn³⁺>Al. The presently described mineral may be referred to as aluminian kanonaite.  相似文献   

The distribution of Fe3+ and Ga3+ between two tetrahedral sites in melilites,Ca2(Mg,Fe3+, Ga,Si)3O7     

Masahide Akasaka  Haruo Ohashi  Isamu Shinno 《Physics and Chemistry of Minerals》1986,13(3):152-155

The distribution of Fe³⁺ and Ga³⁺ between the two tetrahedral sites in three synthetic melilites has been studied by using ⁵⁷Fe Mössbauer spectroscopy. In the melilite, (Ca₂Ga₂SiO₇)₅₀ (Ca₂Fe³⁺GaSiO₇)₅₀ (mol %), the distribution of Fe³⁺ and Ga³⁺ in T1 and T2 sites is apparently random, which can be explained in terms of the electrostatic valence rule. However in the melilites, (Ca₂MgSi₂O₇)₅₂ (Ca₂Fe³⁺GaSiO₇)₄₂ (Ca₂Ga₂SiO₇)₆ and (Ca₂MgSi₂O₇)₆₂ (Ca₂Fe³⁺GaSiO₇)₃₆ (Ca₂Ga₂SiO₇)₂ (mol %), Fe³⁺ shows preference for the more ionic T1 site and Ga³⁺ for the more covalent T2 site. If the electronegativity of Ga³⁺ is assumed to be larger than that of Fe³⁺, the mode of distribution of Fe³⁺ and Ga³⁺ can be explained in terms of our previous hypothesis that a large electronegativity induces a stronger preference for the more covalent T2 site.  相似文献   

Interaction between fluorine and silica in quenched melts on the joins SiO2-AlF3 and SiO2-NaF determined by raman spectroscopy     

Bjørn O. Mysen  David Virgo 《Physics and Chemistry of Minerals》1985,12(2):77-85

The solubility mechanism of fluorine in quenched SiO₂-NaF and SiO₂-AlF₃ melts has been determined with Raman spectroscopy. In the fluorine abundance range of F/(F+Si) from 0.15 to 0.5, a portion of the fluorine is exchanged with bridging oxygen in the silicate network to form Si-F bonds. In individual SiO₄-tetrahedra, one oxygen per silicon is replaced in this manner to form fluorine-bearing silicate complexes in the melt. The proportion of these complexes is nearly linearly correlated with bulk melt F/(F+Si) in the system SiO₂-AlF₃, but its abundance increases at a lower rate and nonlinearly with increasing F/(F+Si) in the system SiO₂-NaF. The process results in the formation ofnonbridging oxygen (NBO), resulting in stabilization of Si₂O ₅ ^2? units as well as metal (Na⁺ or Al³⁺) fluoride complexes in the melts. Sodium fluoride complexes are significantly more stable than those of aluminum fluoride.  相似文献   

Synthesis and physical properties of piemontite Ca2Al3-pMn p 3+ (Si2O7/SiO4/O/OH)     

P. Anastasiou  K. Langer 《Contributions to Mineralogy and Petrology》1977,60(3):225-245

Mn³⁺-bearing piemontites and orthozoisites, Ca₂(Al_3-pMn³⁺ _p)-(Si₂O₇/SiO₄/O/OH), have been synthesized on the join Cz (p = 0.0)-Pm (p = 3.0) of the system CaO-Al₂O₃-(MnO·MnO₂)-SiO₂-H₂O atP = 15 kb,T= 800 °C, and \(f_{O_2 } \) of the Mn₂O₃/MnO₂ buffer. Pure Al-Mn³⁺-piemontites were obtained with 0.5≦p≦1.75, whereas atp=0.25 Mn³⁺-bearing orthozoisite (thulite) formed as single phase product. The limit of piemontite solid solubility is found near p=1.9 at the above conditions. Withp>1.9, the maximum piemontite coexisted with a new high pressure phase CMS-X1, a Ca-bearing braunite (Mn _0.2 ²⁺ Ca_0.8)Mn ₆ ³⁺ O₈(SiO₄), and quartz. Al-Mn³⁺-piemontite lattice constants (LC),b ₀,c ₀,V ₀, increase with increasingp:

相似文献    12. Electron paramagnetic resonance and polarized optical absorption spectra of Ni2+ in synthetic forsterite      H. Rager  S. Hosoya  G. Weiser 《Physics and Chemistry of Minerals》1988,15(4):383-389 The investigated Ni doped forsterite was grown with the floating zone technique. The EPR spectra were taken at room temperature using both 9.5 and 35 GHz. All specimens show EPR signals resulting from Mn2+ at M2 and Fe3+ at M1, M2, and Si positions. Ni2+ EPR signals are observed at 35 GHz but not at 9.5 GHz. The Ni2+ spectra are described by the spin Hamiltonian   相似文献    13. 57Fe mössbauer study of clinopyroxenes in the join CaFe3+ AlSiO6 - CaTiAl2O6      Masahide Akasaka 《Physics and Chemistry of Minerals》1983,9(5):205-211 Synthetic clinopyroxenes of compositions between CaFe3+AlSiO6 and CaFe 0.85 3+ Ti0.15Al1.15Si0.85O6 have been studied by 57Fe Mössbauer spectroscopy. The spectra consist of two doublets assigned to Fe3+ in M1 and T sites. From the area ratios of the doublets the site occupancies of Fe3+ and Al were determined. Si decreases from 1.00 to 0.85 and Al+Fe3+ increases from 1.00 to 1.15 per formula unit with increasing CaTiAl2O6 component of the clinopyroxene. The atomic ratio of Fe3+(T)/Fe3+(total) is 0.11–0.16; 4.5–7.5 percent of the T sites are occupied by Fe3+. Thus the presence of Si-O-Fe3+, Al-O-Fe3+, and Fe3+-O-Fe3+ bonds is expected in addition to Si-O-Si, Si-O-Al and Al-O-Al bonds. However, the possibility of the former bonds being present would be small, because the amount of Fe3+(T) is far less than that of Si and Al. The isomer shift of Fe3+(T) is one of the largest in the values found previously for Fe3+(T) in silicates. It increases with increasing CaTiAl2O6 component and seems to be correlated to the ionic character of the cation — anion bonds calculated from electronegativity. The quadrupole splittings of Fe3+(M1) and Fe3+(T) decrease with the substitution of Fe3+?Ti4+ in the M1 and of Si?Al in the T sites.  相似文献    14. A model for the irradiative coloration of smoky feldspar and the inhibiting influence of water      Anne M. Hofmeister  George R. Rossman 《Physics and Chemistry of Minerals》1985,12(6):324-332 Radiation-induced smoky color and associatedelectron paramagnetic resonance (EPR) signals develop only in potassium feldspar (KAlSi3O8) free of structurally bound molecular water. Fluid inclusion water does not influence coloration. The integrated intensity of each of the four bands (11,600, 16,200, 19,100, and 27,200 cm?1) in the optical absorption spectra are linearly correlated with the doubly-integrated intensity of a broad, asymmetric first derivative atg eff=2.027 in EPR spectra. In microcline, the EPR pattern is resolved into an asymmetric six-line pattern atg eff=2.024 and a single derivative atg eff=2.009 which, based on analogy to alkali-silicate glass, are due respectively to [SiO4/K+]2+ and a hole shared between two nonbonding oxygens on Si. We propose that structural water inhibits formation of smoky centers in feldspar by releasing atomic hydrogen during irradiation which destroys centers while diffusing towards a stable site.  相似文献    15. Statistical chemistry of calcic amphiboles      Dr. S. K. Saxena  T. K. Ekström 《Contributions to Mineralogy and Petrology》1970,26(4):276-284 Principal components analysis is used to study the chemistry of 639 calcic amphiboles. Eigenvectors representing multiple partial correlation coefficients give various sets of substitutional relationships. The relative significance of each set can be noted by the percent variation of the data it represents. The highest percent variation (36%) is associated with the substitutions $$Si + Mg \rightleftharpoons Al^{IV} + Al^{VI} + Ti + Fe^{3 + } + Fe^{2 + } + Na + K$$ . Other expected substitutions among the ions such as AlIV + Na ? Si, the positive correlation between AlIV and AlVI etc. are shown statistically. The substitution of Al in T 1 and T 2 positions imposes an ordering in the M 1, M 2 and M 3 sites. Variability of OH in the amphiboles is found to be significant. There is no definite correlation between OH and Fe3+ but OH and Ti are positively correlated. Under certain conditions and provided the concentration of AlIV does not change significantly, Fe and Mg may be assumed to mix ideally in the amphibole solid solution.  相似文献    16. EPR study of chromium-doped forsterite crystals: Cr<Superscript>3+</Superscript>(<Emphasis Type="Italic">M</Emphasis>1) with and without associated nearest-neighbor Mg<Superscript>2+</Superscript>(<Emphasis Type="Italic">M</Emphasis>2) vacancy      I. D. Ryabov 《Physics and Chemistry of Minerals》2011,38(3):177-184 Electron paramagnetic resonance (EPR) study of single crystals of chromium-doped forsterite grown by the Czochralski method in two different research laboratories has revealed, apart from the known paramagnetic centers Cr3+(M1), Cr3+(M2) and Cr4+, a new center \textCr 3+ (M 1)-V\textMg 2+ (M 2) {\text{Cr}}^{ 3+ } (M 1){-}V_{{{\text{Mg}}^{ 2+ } }} (M 2) formed by a Cr3+ ion substituting for Mg2+ at the M1 structural position with a nearest-neighbor Mg2+ vacancy at the M2 position. For this center, the conventional zero-field splitting parameters D and E and the principal g values and A values of the 53Cr hyperfine splitting have been determined as follows: D = 33.95(3) GHz, E = 8.64(1) GHz, g = [1.9811(2), 1.9787(2), 1.9742(2)], A = [51(3), 52(2), 44(3)] MHz. The center has been identified by comparing EPR spectra with those of the charge-uncompensated ion Cr3+(M1) and the ion pair Cr3+(M1)–Li+(M2) observed in forsterite crystals codoped with chromium and lithium. It has been found that the concentration of the new center decreases to zero, whereas that of the Cr3+(M1) and Cr3+(M1)–Li+(M2) centers increases with an increase of the Li content from 0 up to ~0.03 wt% (at the same Cr content ~0.07 wt%) in the melt. The known low-temperature luminescence data pertinent to the centers under consideration are also discussed.  相似文献    17. Minerals with Brackebuschite-Like Structures: A Novel Solid Solution System Involving Cr<Superscript>6+</Superscript> and V<Superscript>5+</Superscript>      D.?A.?KhaninEmail author  I.?V.?Pekov 《Geology of Ore Deposits》2017,59(7):642-651 A novel complex continuous system of solid solutions involving vauquelinite Pb2Cu(CrO4)(PO4)(OH), bushmakinite Pb2Al(VO4)(PO4)(OH), ferribushmakinite Pb2Fe3+(VO4)(PO4)(OH), and a phase with the endmember formula Pb2Cu(VO4)(PO4)(H2O) or Pb2Cu(VO4)(РО3ОН)(ОН) is studied based on samples from the oxidation zone of the Berezovskoe, Trebiat, and Pervomaisko-Zverevsky deposits in the Urals, Russia. This is the first natural system in which chromate and vanadate anions show a wide range of substitutions and the most extensive solid solution system involving (CrO4)2– found in nature. The major couple substitution is Cr6+ + Cu2+ ? V5+ + M3+, where M = Fe, Al. The correlation coefficients calculated from 125 point analyses are: 0.96 between V and (Fe + Al), 0.96 between Cr and (Cu + Zn),–0.96 between V and (Cu + Zn),–0.97 between Cr and (Fe + Al), and–0.97 between (Fe + Al) and (Cu + Zn). The substitutions V5+ ? Cr6+ (correlation coefficient–0.98) and to a lesser extent P5+ ? As5+ (correlation coefficient–0.86) occur at two types of tetrahedral sites, whereas the metal–nonmetal/metalloid substitutions, i.e., V or Cr for P or As, are minor. The substitution Fe3+ ? Al3+ is also negligible in this solid solution system.  相似文献    18. Luminescence centers in anhydrite,barite, celestite and their synthesized analogs      M. L. Gaft  L. V. Bershov  A. R. Krasnaya  V. Ya. Yaskolko 《Physics and Chemistry of Minerals》1985,11(6):255-260 The intrinsic luminescence center (LC) of SO 4 2? appears at 360 nm in all types of sulfates, but is absent in sulfates with large quantities of impurities. Three nonequivalent Gd3+ LC have been observed in luminescence spectra of anhydrite. Gd3+, Ce3+ O 2 ? LC were established in celestite. Photoluminescence (PL) bands in the sulfates were assigned as follows: the band at 460 nm is related to Eu2+ (a connection with Al3+ or donor-acceptor pair is possible also) in sulfates of Ca and Ba; bands at 520 nm and 590 nm are related to VO4, MoO4 and TiO4 substituting SO4; the band at 660 nm is assigned to Ti3+ X-ray luminescence (XL) band at 620 nm is assigned to Ag+.  相似文献    19. Hydrogen incorporation in orthopyroxene: interaction of different trivalent cations      Roland?StalderEmail author  Stephan?Klemme  Thomas?Ludwig  Henrik?Skogby 《Contributions to Mineralogy and Petrology》2005,150(5):473-485 The incorporation of hydrogen into ferrosilite, Fe-bearing enstatite and orthopyroxene containing different trivalent cations (Cr3+ and Al3+, Cr3+ and Fe3+) was investigated experimentally at 25 kbar. Hydrogen concentration was determined by FTIR-spectroscopy on oriented crystal sections and by secondary ion mass spectroscopy, whereas Mößbauer spectroscopy and optical spectroscopy were used to characterise the valence state of Fe in orthopyroxene. Results suggest that hydrogen incorporation in ferrosilite is achieved by a similar mechanism as in pure enstatite. In Cr-bearing samples, however, hydrogen incorporation is reduced by the presence of other trivalent cations by an increased tendency to form Tschermaks substitutions, e.g. Si T 4+ + Mg M1 2+ ? Al T 3+ + Cr M1 3+ . Thus, hydrogen solubility in natural orthopyroxenes from the Earth’s mantle, containing significant amounts of Cr3+, Al3+, and Fe3+, may be much more limited than expected from their trivalent cation content, as a large fraction of the trivalent cations does not participate in H-incorporating reactions as 2 Mg M1 2+ ? M M1 3+ + VM1 + H i + .  相似文献    20. Structure analysis on synthetic emerald crystals      Pei-Lun Lee  Jiann-Shing Lee  Eugene Huang  Ju-Hsiou Liao 《Physics and Chemistry of Minerals》2013,40(5):439-446 Single crystals of emerald synthesized by means of the flux method were adopted for crystallographic analyses. Emerald crystals with a wide range of Cr3+-doping content up to 3.16 wt% Cr2O3 were examined by X-ray single crystal diffraction refinement method. The crystal structures of the emerald crystals were refined to R 1 (all data) of 0.019–0.024 and wR 2 (all data) of 0.061–0.073. When Cr3+ substitutes for Al3+, the main adjustment takes place in the Al-octahedron and Be-tetrahedron. The effect of substitution of Cr3+ for Al3+ in the beryl structure results in progressively lengthening of the Al–O distance, while the length of the other bonds remains nearly unchanged. The substitution of Cr3+ for Al3+ may have caused the expansion of a axis, while keeping the c axis unchanged in the emerald lattice. As a consequence, the Al–O–Si and Al–O–Be bonding angles are found to decrease, while the angle of Si–O–Be increases as the Al–O distance increases during the Cr replacement.  相似文献

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