A geochemical model for evaluating theories on the genesis of Florida''s sedimentary phosphate deposits

Present ionic concentrations of Ca ⁺⁺,HCO ₃ ^- ,and HPO ₄ ⁼ in surface and groundwater runoff in Florida indicate that phosphorus is being concentrated in rock through dissolution and reprecipitation, with calcium phosphate increasing at the expense of calcium carbonate. Analog computer simulation of a systems model of this process suggests that significant enrichment can occur in 20 million years. The degree of enrichment depends on the supply of new phosphorus to Florida through rain and oceanic exchange processes. If the calcium phosphate content of original rock is 0.5 to 1.0 percent (0.52 to 1.05 percent P ₂ O ₅),a formation with 10 to 20 percent calcium phosphate (CaPO ₄ or 10.5 to 21.0 percent P ₂ O ₅)as in the Hawthorn Formation (Miocene)may result. Nutrient upwelling along the continental slope coupled with transport to the estuaries by lateral eddy diffusion can supply an additional 400 mg P|m ² |yr which, if deposited, would result in a sediment with a 4.3 percent CaPO ₄ (4.5 percent P ₂ O ₅)content. If this is enriched later by resolution, 40 percent CaPO ₄ (42 percent P ₂ O ₅)results. Through geologic time, the ocean may be considered as a source of phosphorus to the land through rain or estuarine sediment.     

57Fe Mössbauer spectroscopy and magnetization of cation-deficient Fe2TiO4 and FeCr2O4. Part I:57Fe Mössbauer spectroscopy

⁵⁷Fe Mössbauer spectra are presented for synthetic cation-deficient Fe₂TiO₄ and FeCr₂O₄ spinel particles (<1μm) at various temperatures. The spectra of ferrimagnetic cation-deficient Fe₂TiO₄ show characteristic features due to relaxation because of superparamagnetism and spin relaxation in the temperature range 5–294 K. At 5 K and 78 K, a superposition of at least two sextets is observed which appear to arise from Fe³⁺ onA-sites (Fe _A ³⁺ andB-sites (Fe _B ³⁺ ) of the spinal lattice with magnetic hyperfine fields at 5 K ofB _hf ((Fe _B ³⁺ )≈47.5 T andB _hf (Fe _B ³⁺ )≈51.0 T, respectively. Cation-deficient FeCr₂O₄ particles reveal at 78 K a fieldB _hf (Fe³⁺)≈46.9 T and exhibit relaxation spectra as a consequence of superparamagnetism in the temperature range 80 K - ～300 K. At 294 K, quadrupole splitting Δ(Fe _A ³⁺ )=0.92 mm/s and isomer shift δ(Fe _A ³⁺ )=0.29 mm/s (relative to metallic Fe) are measured. For both compounds the magnetic hyperfine fieldsB _hf are discussed in terms of supertransferred hyperfine fields involving vacancies and in the case of cation-deficient Fe₂TiO₄ also diamagnetic Ti⁴⁺ neighbours of the Fe ions.     

A new Cu-rich variety of lyonsite from fumarolic sublimates of the Tolbachik volcano (Kamchatka, Russia) and its crystal structure

A new Cu-rich variety of lyonsite has been found from fumarolic sublimates of the Tolbachik volcano (Kamchatka, Russia). The empirical formula is Cu_4.33Fe _2.37 ³⁺ Ti_0.26Al_0.26Zn_0.07(V_5.85As_0.07Mo_0.07P_0.01S_0.01)O₂₄. The crystal structure was studied on single crystal using synchrotron radiation, R = 0.0514. The mineral is orthorhombic, Pnma, a = 5.1736(7), b =10.8929(12), c = 18.220(2) Å, V = 1026.8(2) ų, and Z = 2. The structural formula is (Cu_0.6Ti_0.3Al_0.3Fe _0.2 ³⁺ □_0.6)_Σ2Cu₂(Fe _2.2 ³⁺ Cu_1.8)_Σ4(V_5.8As_0.1Mo_0.1)_Σ6O₂₄. It is proposed to recast the simplified formula of lyonsite as Cu_3+x (Fe _4?2x ³⁺ Cu_2x )(VO₄)₆, where 0 ≤ x ≤ 1.     

A computer model for the cubic sodalite structure

A computer model for cubic sodalite structures, general formula M ₈(T ₁₂O₂₄)X ₂ where M, X and T are the cavity cation and anion and framework cation respectively, has been devised. It has been used to determine the effect of changing cavity cation and anion radii on the cell edge, tilt angle of the tetrahedra and T-O-T angle for the following sodalite frameworks: (Al₆Si₆O₂₄)^6?, (Be₆Si₆O₂₄)^12?, (Al₁₂O₂₄)^12?, and (B₁₂O₂₄)^12?. After fixing the T-O distance(s), the cavity cation-framework oxygen distance and taking a value of 1.4 Å for the radius of oxygen the model was used to calculate atomic coordinates and interatomic distances and angles for selected aluminosilicate-sodalites. The structure calculated for Na₈(Al₆Si₆O₂₄)Cl₂ agrees closely with that determined for natural sodalite (Löns and Schulz, 1967). The model is also applied to the estimation of the effective radii of the tetrahedrally-coordinated cavity anions which can be accommodated in natural and synthetic sodalites: OH^? 1.48–1.51, Cl^? 1.78, Br^? 1.93, I^? 2.14–2.17, SO ₄ ^2? 2.37–2.57, MoO ₄ ^2? 2.70 and WO ₄ ^2? 2.79 Å.     

Urban land-use effects on groundwater phosphate distribution in a shallow aquifer, Nanfei River basin, China

Groundwater, surface water, soil and river sediment samples, and information on land use in the Nanfei River basin (NRB) of China have been analyzed to study the geochemistry, distribution, and mobilization of phosphorus. The distribution of phosphate (PO ₄ ^3??/sup> ) and the relationships between PO ₄ ^3??/sup> and several constituents in groundwater were studied. Partial correlation analysis relating PO ₄ ^3??/sup> to types of land use was conducted using the data analyzing tool SPSS 15.0. The processes controlling the transport of PO ₄ ^3??/sup> are discussed. The conclusions from this study are: (1) urban land use has obvious impact on PO ₄ ^3??/sup> in groundwater, the average concentration of PO ₄ ^3??/sup> being 4.37?mg/L, greater than that resulting from farmland and mixed land use, which have average PO ₄ ^3??/sup> concentrations of 0.10 and 0.18?mg/L, respectively; (2) the partial correlation between PO ₄ ^3??/sup> and types of land use is significant with a coefficient of 0.760; (3) the PO ₄ ^3??/sup> concentrations in surface water are generally higher than those in groundwater, and the total phosphorus (TP) concentrations in river sediments are generally higher than those in soil samples; (4) groundwater is a carrier of PO ₄ ^3??/sup> and is likely responsible for the redistribution of PO ₄ ^3??/sup> in different regions of NRB.     

Hydrogen and carbon in solid solution in oxides and silicates

The dissolution of H₂O and CO₂ in structurally dense, nominally anhydrous and non-carbonate oxide matrices such as MgO and CaO is reviewed. H₂O and CO₂ are treated as gaseous oxide components which enter into solid solution with the refractory oxide hosts. They form anion complexes associated with cation vacancy sites. Evidence is presented that OH^? pairs which derive from the dissolution of H₂O are subject to a charge transfer (CT) conversion into peroxy moieties and molecular hydrogen, O ₂ ^2? ... H₂. Because the O ₂ ^2? moiety is small (O^?-O^? distance ≈ 1.5 Å) high pressure probably favors the CT conversion. Mass spectroscopic studies show that molecular H₂ may be lost from the solid which retains excess oxygen in the form of O ₂ ^2? , leading to the release of atomic O. The dissociation of O ₂ ^2? moieties into a vacancy-bound O^? state and an unbound O^? state can be followed by measuring the internal redox reactions involving transition metal impurities, the transient paramagnetism of the O^? and their effect on the d.c. conductivity. Evidence is presented that CO₂ molecules dissolve dissociatively in the structurally dense oxide matrix, as if they were first to dissociate into CO+O and then to form separate solute moieties CO ₂ ^2? and O ₂ ^2? , both associated with cation vacancy sites. In the CO ₂ ^2? moiety (C-O^? distance 1.2–1.3 Å, OCO angle ≈ 130°) the C atom probably sits off center. The transition of the C atom into interstitial sites is accompanied by dissociation of the CO ₂ ^2? moiety into CO^? and O^?. This transition can be followed by infrared spectroscopy, using OH^? as local probes. Further support derives from magnetic susceptibility, thermal expansion, low frequency dielectric loss and low temperature deformation measurements. The recently observed emission of O and Mg atoms besides a variety of molecules such as CO, CO₂, CH₄, HCN and other hydrocarbons during impact fracture of MgO single crystals is presented and discussed in the light of the other experimental data.     

Ab initio calculations of 17O and nT NMR parameters (nT=31P, 29Si) in H3 TOTH3 dimers and T 3O9 trimeric rings

NMR shieldings (σ) and electric field gradients (eq) are calculated using ab initio methods at the O and T nuclei (where T=P, Si) in two different types of molecules-TH₃ dimers, i.e. H₃SiOSiH₃ and H₃POPH ₃ ²⁺ , and TO₄ trimeric rings, i.e., Si₃O ₉ ^6- and P₃O ₉ ^3- , which serve as models for assessing the effects of polymerization, bond length and bond angle variation on the NMR properties of polymerized silicates and phosphates. In agreement with earlier ab initio studies on H₃SiOSiH₃ we confirm that σ(²⁹Si), σ(³¹P), σ(¹⁷O) and eq(¹⁷O) all decrease as θ(SiOSi) decreases in the range from 180° to 100°. However, correction for artifacts due to distant core electrons leads to a considerably reduced value for the anisotropy in σ ^O, bringing it into better agreement with estimated experimental values. The qualitative change in σ(²⁹Si) with θ(SiOSi) can be understood on the basis of changes in the energies of the highest energy occupied MO's and consequent variations in their contributions to the paramagnetic part of the shielding. For H₃POPH ₃ ²⁺ we calculate a larger value of eq^O than for the analog Si compound but the same type of variation of σ(¹⁷O) with θ(TOT). The change in σ(³¹P) with θ(POP) is, however, calculated to be much smaller than in the Si case and a maximum is predicted for intermediate angles. For the trimeric rings we obtain energy optimized geometries in good agreement with x-ray structural data, with T-O terminal distances systematically shorter than the T-O bridging distances. Calculated σ(T) anisotropies are also in good agreement with experiment and can be simply related to the calculated structure. After correction for distant core effects we obtain a change in σ(³¹P) between PO ₄ ^3- and P₃O ₉ ^3- in reasonable agreement with experiment.     

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

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:

Zn and Pb solubility and speciation in aqueous chloride fluids at T-P parameters corresponding to granitoid magma degassing and crystallization

The solubility of all possible Zn and Pb species in aqueous chloride fluids was evaluated by means of thermodynamic simulations in systems ZnO(PbO)-aqueous solution of NaCl (KCl, NaCl + HCl) within broad ranges of temperature (600–900°C), pressure (0.7–5 kbar), and chloride concentrations, under parameters corresponding to the crystallization and degassing of granitoid magmas in the Earth’s crust. Our simulation results demonstrate that the addition of Cl to the fluid phase in the form of Na(K)Cl and HCl significantly increases the concentrations of Cl-bearing Zn and Pb complexes and the total concentration of the metals in the solutions in equilibrium with the solid oxides. In Zn-bearing fluids, the Zn(OH) ₂ ⁰ , ZnOH⁺, and Zn(OH) ₃ ^? —hydroxyl complexes and the ZnCl ₂ ⁰ , and ZnCl⁺ chlorocomplexes, which are predominant at low Cl concentrations (C_Cl < 0.05–0.1 m) give way to ZnCl ₄ ^2? with increasing C_Cl, which becomes the predominant Zn species of the fluid at C_Cl > 0.1–0.5 m throughout the whole temperature range in question and pressures higher than 1 kbar. For Pb-bearing fluids, the T-P-X region dominated by the Pb(OH) ₂ ⁰ , and Pb(OH) ₃ ^? hydroxyl complexes is remarkably wider than the analogous region for Zn, particularly at elevated temperatures (≥700°C) in alkaline solutions. An increase in C_Cl is associated with an increase in the concentration and changes in the speciation of Pb chlorocomplexes: PbCl ₂ ⁰ → PbCl ₃ ^? → PbCl ₄ ^2? . The concentrations of Zn and Pb chlorocomplexes increase with increasing pressure, decreasing temperature, and decrease pH with the addition of HCl to the system. It is demonstrated that the solubility of ZnO at any given T-P-X in alkaline solutions with low chloride concentrations are lower than the solubility of PbO. The Zn concentration increases more significantly than with the Pb concentration with increasing C_Cl and decreasing pH, so that the Zn concentration in acidic solutions is higher than the Pb concentration over broad ranges of temperature, pressure, and Cl concentration. Chloride complexes of Zn (ZnCl ₂ ⁰ , and ZnCl ₄ ^2? ) and Pb (PbCl ₂ ⁰ , and PbCl ₃ ^? are proved to be predominant within broad T-P-X-pH ranges corresponding to the parameters under which magmatic fluid are generated. Our simulation results confirm the hypothesis that chlorocomplexes play a leading role in Zn and Pb distribution between aqueous chloride fluids and granitic melts. These simulation results are consistent with experimental data on the Zn and Pb distribution coefficients (D(Zn)^f/m and D(Pb)^f/m, respectively) between aqueous chloride fluids and granitic melts that demonstrated that (1) D(Zn)^f/m and D(Pb)^f/m increase with increasing Na and K chloride concentrations in the aqueous fluid, (2) both D(Zn)^f/m and D(Pb)^f/m drastically increase when HCl is added to the fluid, and (3) (D(Zn)^f/m is higher than D(Pb)^f/m at any given T-P-X parameters. The experimentally established decrease in D(Zn)^f/m and D(Pb)^f/m with increasing pressure (at unchanging temperature and Cl concentration) is likely explained by an increase in the alkalinity of the aqueous chloride fluid in equilibrium with granite melt and, correspondingly, a decrease in the Zn and Pb solubility in this fluid.     

The effect of medium chemistry on the solubility and morphology of brushite crystals

An experimental study of the particulars of the solubility and crystallization of brushite Ca(HPO₄) · 2H₂O from aqueous solution in conditions of a variable pH (6.0–3.0) and the contents of impurity ions (K⁺, Na⁺, NH ₄ ⁺ , Mg²⁺, SO ₄ ^2? , CO ₃ ^2? ) has been conducted. It is established that brushite solubility markedly rises with a decrease in pH from 6 to 3 and slightly rises with an increase in Mg²⁺ and SO ₄ ^2? concentrations. The enrichment in K⁺, Na⁺, and NH ₄ ⁺ does not affect brushite solubility. The changeable chemistry of the medium results in variation of the synthetic crystal habit, from rhombic tabular to thickened prismatic crystals.     

Perrierite-(La), (La,Ce,Ca)4(Fe2+,Mn)(Ti,Fe3+,Al)4(Si2O7)2O8, a new mineral species from the Eifel volcanic district, Germany

Non-metamict perrierite-(La) discovered in the Dellen pumice quarry, near Mendig, in the Eifel volcanic district, Rheinland-Pfalz, Germany has been approved as a new mineral species (IMA no. 2010-089). The mineral was found in the late assemblage of sanidine, phlogopite, pyrophanite, zirconolite, members of the jacobsite-magnetite series, fluorcalciopyrochlore, and zircon. Perrierite-(La) occurs as isolated prismatic crystals up to 0.5 × 1 mm in size within cavities in sanidinite. The new mineral is black with brown streak; it is brittle, with the Mohs hardness of 6 and distinct cleavage parallel to (001). The calculated density is 4.791 g/cm³. The IR spectrum does not contain absorption bands that correspond to H₂O and OH groups. Perrierite-(La) is biaxial (-), α = 1.94(1), β = 2.020(15), γ = 2.040(15), 2V _meas = 50(10)°, 2V _calc = 51°. The chemical composition (electron microprobe, average of seven point analyses, the Fe²⁺/Fe³⁺ ratio determined from the X-ray structural data, wt %) is as follows: 3.26 CaO, 22.92 La₂O₃, 19.64 Ce₂O₃, 0.83 Pr₂O₂, 2.09 Nd₂O₃, 0.25 MgO, 2.25 MnO, 3.16 FeO, 5.28 Fe₂O₃, 2.59 Al₂O₃, 16.13 TiO₂, 0.75 Nb₂O₅, and 20.06 SiO₂, total is 99.21. The empirical formula is (La_1.70Ce_1.45Nd_0.15Pr_0.06Ca_0.70)_Σ4.06(Fe _0.53 ²⁺ Mn_0.38Mg_0.08)_Σ0.99(Ti_2.44Fe _0.80 ³⁺ Al_0.62Nb_0.07)_Σ3.93Si_4.04O₂₂. The simplified formula is (La,Ce,Ca)₄(Fe²⁺,Mn)(Ti,Fe³⁺,Al)₄(Si₂O₇)₂O₈. The crystal structure was determined by a single crystal. Perrierite-(La) is monoclinic, space group P2₁/a, and the unit-cell dimensions are as follows: a =13.668(1), b = 5.6601(6), c = 11.743(1) Å, β = 113.64(1)°; V = 832.2(2) ų, Z = 2. The strong reflections in the X-ray powder diffraction pattern are [d, Å (I, %) (hkl)]: 5.19 (40) (110), 3.53 (40) ( $\overline 3 $ 11), 2.96 (100) ( $\overline 3 $ 13, 311), 2.80 (50) (020), 2.14 (50) ( $\overline 4 $ 22, $\overline 3 $ 15, 313), 1.947 (50) (024, 223), 1.657 (40) ( $\overline 4 $ 07, $\overline 4 $ 33, 331). The holotype specimen of perrierite-(La) is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, with the registration number 4059/1.     

Laihunite—A new iron silicate mineral

Laihuite reported in the present paper is a new iron silicate mineral found in China with the following characteristics:

1. This mineral occurs in a metamorphic iron deposit, associated with fayalite, hypersthene, quartz, magnetitc, etc.
2. The mineral is opaque, black in colour, thickly tabular in shape with luster metallic to sub-metallic, two perfect cleavages and specific gravity of 3.92.
3. Its main chemical components are Fe and Si with Fe³⁺>Fe²⁺. The analysis gave the formula of Fe Fe _1.00 ³⁺ ·Fe _0.58 ²⁺ ·Mg _0.03 ²⁺ ·Si_0.96O₄.
4. Its DTA curve shows an exothermic peak at 713°C.
5. The mineral has its own infrared spectrum distinctive from that of other minerals.
6. This mineral is of orthorhombic system; space group:C _2h ^/5 ?P2₁/c; unit cell:α=5.813ű0.005,b=4.812ű0.005,c=10.211ű0.005,β=90.87°.
7. The Mössbauer spectrum of this mineral is given, too.

     

The crystal chemistry of lithium and Fe3+ in synthetic orthopyroxene

Lithian ferrian enstatite with Li₂O = 1.39 wt% and Fe₂O₃ 7.54 wt% was synthesised in the (MgO–Li₂O–FeO–SiO₂–H₂O) system at P = 0.3 GPa, T = 1,000°C, fO₂ = +2 Pbca, and a = 18.2113(7), b = 8.8172(3), c = 5.2050(2) Å, V = 835.79(9) Å³. The composition of the orthopyroxene was determined combining EMP, LA-ICP-MS and single-crystal XRD analysis, yielding the unit formula ^M2(Mg_0.59Fe _0.21 ²⁺ Li_0.20) ^M1(Mg_0.74Fe _0.20 ³⁺ Fe _0.06 ²⁺ ) Si₂O₆. Structure refinements done on crystals obtained from synthesis runs with variable Mg-content show that the orthopyroxene is virtually constant in composition and hence in structure, whereas coexisting clinopyroxenes occurring both as individual grains or thin rims around the orthopyroxene crystals have variable amounts of Li, Fe³⁺ and Mg contents. Structure refinement shows that Li is ordered at the M2 site and Fe³⁺ is ordered at the M1 site of the orthopyroxene, whereas Mg (and Fe²⁺) distributes over both octahedral sites. The main geometrical variations observed for Li-rich samples are actually due to the presence of Fe³⁺, which affects significantly the geometry of the M1 site; changes in the geometry of the M2 site due to the lower coordination of Li are likely to affect both the degree and the kinetics of the non-convergent Fe²⁺-Mg ordering process in octahedral sites.     

Lavoisierite, Mn2+ 8[Al10(Mn3+Mg)][Si11P]O44(OH)12, a new mineral from Piedmont, Italy: the link between “ardennite” and sursassite

The new mineral species lavoisierite, ideally Mn²⁺ ₈[Al₁₀(Mn³⁺Mg)][Si₁₁P]O₄₄(OH)₁₂, has been discovered in piemontite-bearing micaschists belonging to the Piedmontese Nappe from Punta Gensane, Viù Valley, Western Alps, Italy. It occurs as yellow-orange acicular to prismatic-tabular crystals up to a few millimeters in length, with white streak and vitreous luster, elongated along [010] and flattened on {001}. Lavoisierite is associated with quartz, “mica,” sursassite, piemontite, spessartine, braunite, and “tourmaline.” Calculated density is 3.576 g cm^?3. In plane-polarized light, it is transparent, pleochroic, with pale yellow parallel to [010] and yellow-orange normal to this direction; extinction is parallel and elongation is positive. Birefringence is moderate; the calculated average refraction index n is 1.750. Lavoisierite is orthorhombic, space group Pnmm, with a 8.6891(10), b 5.7755(3), c 36.9504(20) Å, V 1854.3(2) Å³, Z = 2. Calculated main diffraction lines of the X-ray powder diffraction pattern are [d in Å, (I), (hkl); relative intensities are visually estimated]: 4.62 (m) (112), 2.931 (vs) (1110), 2.765 (s) (1111), 2.598 (s) (310), 2.448 (ms) (028). Chemical analyses by electron microprobe give (in wt%) P₂O₅ 2.08, V₂O₅ 0.37, SiO₂ 34.81, TiO₂ 0.13, Al₂O₃ 22.92, Cr₂O₃ 0.32, Fe₂O₃ 0.86, Mn₂O₃ 6.92, MnO 19.09, MgO 5.73, CaO 1.94, Na₂O 0.01, H₂O 5.44, sum 100.62 wt%. H₂O content was calculated from structure refinement. The empirical formula, based on 56 anions, is (Mn _5.340 ²⁺ Mg_1.810Ca_0.686Na_0.006)_Σ=7.852(Al_8.921Mn _1.739 ³⁺ Mg_1.010Fe _0.214 ³⁺ Cr_0.084Ti_0.032)_Σ=12.000(Si_11.496P_0.582V_0.081)_Σ=12.159O_43.995(OH)_12.005. The crystal structure of lavoisierite was solved by direct methods and refined on the basis of 1743 observed reflections to R ₁ = 4.6 %. The structure is characterized by columns of edge-sharing octahedra running along [010] and linked to each other by means of [SiO₄], [Si₂O₇], and [Si₃O₁₀] groups. Lavoisierite, named after the French chemist and biologist Antoine-Laurent de Lavoisier (1743–1794), displays an unprecedented kind of structure, related to those of “ardennite” and sursassite.     

Optical absorption spectra of iron ions in vivianite

Absorption bands are determined in polarized optical spectra of vivianite Fe₃(PO₄)₂·8H₂O, recorded at room and low temperatures. These bands are caused by spin-allowed d-d transitions in structurally nonequivalent Fe _A ²⁺ (～11000 cm^-1 (γ-polarization) (and) ～12000 cm^-1 (β-polarization)) (and) Fe _B ²⁺ (～8400 cm^-1 (γ, α-polarization) and ～11200 cm^-1 (α-polarization)) ions. A charge transfer band (CTB) Fe _B ²⁺ +Fe _B ³⁺ →Fe _B ²⁺ +Fe _B ²⁺ (～15000 cm^-1) also determined, has polarizing features giving evidence of a change in the Fe _B ²⁺ -Fe _B ³⁺ bond direction, when compared with Fe _B ²⁺ -Fe _B ²⁺ . Bands of exchange-coupled Fe³⁺-Fe³⁺ pairs (～19400, ～20400, ～21300 and ～21700 cm^-1) which appear on oxidation of Fe²⁺ in paired Fe _B octahedra are also characterized.     

Depmeierite Na8[Al6Si6O24](PO4,CO3)1−x · 3H2O (x < 0.5): A new cancrinite-group mineral species from the Lovozero alkaline pluton of the Kola Peninsula

A new mineral depmeierite, the first cancrinite-group member with the species-forming extraframework anion PO ₄ ^3? , has been found at Mt. Karnasurt in the Lovozero alkaline pluton on the Kola Peninsula in Russia. Natrolite and depmeierite are the major components of a hydrothermal peralkaline veinlet 1.5 cm thick, which cross cuts the foyaite-urtite-lujavrite complex. The associated minerals are steenstrupine-(Ce), vuonnemite, epistolite, sodalite, aegirine, serandite, natisite, and vitusite-(Ce). Depmeierite occurs as colorless transparent isometric grains up to 1 cm in size. Its luster is vitreous. The mineral is brittle, and its cleavage (100) is perfect. Its Mohs hardness is 5, and D(meas) = 2.321(1) and D(calc) = 2.313 g/cm³. Depmeierite is optically biaxial positive, ω = 1.493(2), and ? = 1.497(2). The IR spectrum is given. The chemical composition is as follows (wt %, the average of 10 microprobe analyses with the H₂O and CO₂ determined by selective sorption): 23.04 Na₂O, 0.54 K₂O, 0.03 Fe₂O₃, 29.07 Al₂O₃, 36.48 SiO₂, 3.30 P₂O₅, 0.08 SO₃, 0.97 CO₂, and 5.93 H₂O; the total is 99.44. The empirical formula based on (Si,Al)₁₂O₂₄ is (Na₇₅₈K_0.12)_Σ7.70(Si_6.19Al_5.81O₂₄)[(PO₄)_0.47(CO₃)_0.22(OH)_0.02(SO₄)_0.01]_Σ0.72 · 3.345H₂O. The simplified formula is Na₈[Al₆Si₆O₂₄](CO₃)_{1 ? x} · 3H₂O (x < 0.05). Depmeierite is hexagonal with space group P6₃, and the unit-cell dimensions are a = 12.7345(2), c = 5.1798(1), V = 727.46(2) ų, and Z = 1. The strongest reflections of the X-ray powder pattern (d, Å (I, %) [hkl]) are as follows: 6.380(30) [110], 4.695(91) [101], 3.681(37) [300], 3.250(100) [211], 2.758 (33) [400], 2.596(31) [002], and 2.121(24) [330, 302]. The crystal structure was studied using a single crystal, and R _hkl = 0.0362. Depmeierite differs from cancrinite in the development of wide channels containing Na cations, H₂O molecules, prevailing PO ₄ ^3? -anionic groups, and CO ₃ ^2? . The mineral is named in honor of the German crystallographer Wulf Depmeier (born in 1944). The type specimen is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow. The cancrinite sensu stricto subgroup separated within the cancrinite group comprises six minerals with AB frameworks, the smallest unit cell is (a ≈ 12.55–12.75, c ≈ 5.1–5.4 Å), and the chain […Na…H₂O…]^∞ exists in narrow channels: cancrinite, vishnevite, cancrisilite, hydroxycancrinite, kyanoxalite, and depmeierite. The P-bearing varieties of the cancrinite-group minerals are discussed, as well as the formation conditions of the noncarbonate members of the group related to intrusive alkaline complexes.     

Electrokinetic Stabilization of Soft Soil Using Carbonate-Producing Bacteria

The carbonate (CO ₃ ^?2 ) produced by Sporosarcina pasteurii was injected electrokinetically to enhance the mechanical properties of soft clay soils. In this method the Ca²⁺ was injected into the anode chamber and moved towards the cathode by electromigration and electroosmotic flow. Then the released CO ₃ ^?2 from a blend of bacteria and urea was injected into the cathode chamber. The CO ₃ ^?2 ions were moved from the cathode to the anode under electromigration mechanism. The CaCO₃ was precipitated in the presence of calcium in porous medium of the soil, and consequently increased the shear strength of the soil. The polarity reversal was applied to have a homogeneous distribution of CaCO₃.     

Theoretical studies of the electronic structure of copper in tetrahedral and triangular coordination with sulfur

Molecular orbital calculations are presented for the copper-sulfur polyhedral clusters CuS ₄ ^7? , CuS ₄ ^6? , CuS ₃ ^5? and CuS ₃ ^4? , which occur in many minerals. Calculated and experimental optical and X-ray energies are found to be in good agreement. The crystal field orbitals of Cu⁺ in tetrahedrally coordinated sulfides are found to be less tightly bound than the S3p nonbonding orbitals by about 2–3 eV whereas the e and t ₂ crystal field orbitals are split by about 1 eV. The crystal field splitting of Cu²⁺ in tetrahedral coordination is about 0.7–0.8 eV while the separation of the S3p nonbonding orbitals and the partially filled t ₂ crystal field orbital is about 2 eV. In triangular coordination both the Cu⁺ and Cu²⁺ crystal field orbitals are more stable than in tetrahedral coordination, more widely split and more strongly mixed with the S3p orbitals. CuS is shown to be unstable as the mixed oxidation state compound Cu^2+III (Cu^+IV)₂S^2?(S ₂ ^2? ); rather each Cu is predicted to have a fractional oxidation state and partially-empty crystal field orbitals.     

Carbon Dioxide in igneous petrogenesis: I

A number of experimental CO₂ solubility data for silicate and aluminosilicate melts at a variety of P- T conditions are consistent with solution of CO₂ in the melt by polymer condensation reactions such as SiO _4(m ^4? +CO_2(v)+Si _n O _3n+1(m) ⁽²ⁿ⁺¹⁾ ?Si _n+1O _3n+4(m) ^(2n+4)? +CO _3(m ^)2? . For various metalsilicate systems the relative solubility of CO₂ should depend markedly on the relative Gibbs free change of reaction. Experimental solubility data for the systems Li₂O-SiO₂, Na₂O-SiO₂, K₂O-SiO₂, CaO-SiO₂, MgO-SiO₂ and other aluminosilicate melts are in complete accord with predictions based on Gibbs Free energies of model polycondesation reactions. A rigorous thermodynamic treatment of published P- T-wt.% CO₂ solubility data for a number of mineral and natural melts suggests that for the reaction CO_2(m) ? CO_2(v)

1. CO₂-melt mixing may be considered ideal (i.e., { \(a_{{\text{CO}}_{\text{2}} }^m = X_{{\text{CO}}_{\text{2}} }^m \) );
2. \(\bar V_{{\text{CO}}_{\text{2}} }^m \) , the partial molal volume of CO₂ in the melt, is approximately equal to 30 cm³ mole^?1 and independent of P and T;
3. Δ C _p ⁰ is approximately equal to zero in the T range 1,400° to 1,650 °C and
4. enthalpies and entropies of the dissolution reaction depend on the ratio of network modifiers to network builders in the melt. Analytic expressions which relate the CO₂ content of a melt to P, T, and \(f_{{\text{CO}}_{\text{2}} } \) for andesite, tholeiite and olivine melilite melts of the form

$$\ln X_{{\text{CO}}_{\text{2}} }^m = \ln f_{{\text{CO}}_{\text{2}} } - \frac{A}{T} - B - \frac{C}{T}(P - 1)$$ have been determined. Regression parameters are (A, B, C): andesite (3.419, 11.164, 0.408), tholeiite (14.040, 5.440,0.393), melilite (9.226, 7.860, 0.352). The solubility equations are believed to be accurate in the range 3<P<30 kbar and 1,100°<T<1,650 °C. A series of CO₂ isopleth diagrams for a wide range of T and P are drawn for andesitic, tholeiitic and alkalic melts.