A statistical-chemical and thermodynamic approach to the study of lunar mineralogy     

S.K. Saxena  L.S. Walter 《Geochimica et cosmochimica acta》1974,38(1):79-95

Principal components analysis is used to study the chemical compositions of pyroxenes of five Apollo 12 specimens. Important correlations recognized in the variation of oxide weight per cent are: MGO, Al₂O₃, SiO₂| CaO, TiO₂, FeO MgO, Al₂O₃, SiO₂| FeO MgO, SiO₂, FeO | Al₂O₃, CaO, TiO₂ where the oxides on one side of the bar are correlated positively with each other and negatively with the oxides on the other side. Several other similarly distinct relationships with significantly less variance could be noted. These correlations indicating substitutional relationships can be interpreted as representative of stable and metastable trends of crystallization by using crystal-chemical and thermodynamic information. The per cent variance of pyroxene groups with characteristic trends in each specimen can be evaluated and interpreted in terms of history of crystallization. Distribution of Fe and Mg in certain pairs of olivine and pyroxene, which are found in contact in the rock and which may have crystallized simultaneously, is useful in recognizing the tendency towards chemical equilibrium in FeMg distribution during a limited interval in the liquidus or subsolidus stages.  相似文献   

Cation distribution in low-calcium pyroxenes: Dependence on temperature and calcium content and the thermal history of lunar and terrestrial pigeonites     

Surendra K. Saxena  Subrata Ghose  A.C. Turnock 《Earth and Planetary Science Letters》1974,21(2):194-200

Four pyroxenes with compositions En₄₈Fs₄₈Wo₄, En_47·5Fs_47·5Wo₅, En₄₅Fs₄₅Wo₁₀ and En₄₀Fs₄₀Wo₂₀, synthesized at 1200°C at atmospheric pressure, were heat-treated at 500, 600, 700, and 800°C for various lengths of time. These pyroxenes are variously ordered with respect to Fe²⁺ and Mg²⁺ without unmixing. The Fe²⁺-Mg²⁺ distribution over the two nonequivalent sites M1 and M2, determined through Mössbauer spectroscopy, is found to be a function of both temperature and concentration of Ca²⁺ at the M2 site. The preference of Fe²⁺ for the M2 site increases with decreasing temperature and increasing Ca²⁺. These data can be used to determine cation equilibration temperatures of lunar and terrestrial pigeonites. The lunar pigeonites usually indicate equilibration temperatures of 700–860°C, except the pigeonite from rock 14053, which may have been subjected to shock heating due to meteoritic impact.  相似文献   

Silicate solid solutions and geothermometry     

Dr. S. K. Saxena 《Contributions to Mineralogy and Petrology》1969,23(2):140-156

Principal component analysis, using eigenvalues and eigenvectors, of the encountered variation in the chemistry of 153 garnets indicates the following: (1) In low grade metamorphic rocks, spessertite and almandine are distinctly isomorphous. The variability of pyrope content does not influence the binary Fe-Mn relationship. However there may be some influence of the grossularite content. (2) In high grade metamorphic rocks, pyrope and almandine are distinctly isomorphous. Variability of grossularite content does not affect the binary Mg-Fe relationship. However, variability in spessertite content may influence the linearity particularly when there is little pyrope.Similar statistical analysis of the chemical data on 119 samples of clinopyroxenes indicates that only significant changes in the concentrations of Al in octahedral and/or of Al in tetrahedral sites and Ti could cause some change in the FeMg ratio in the mineral.Principal component analysis of the data on coexisting garnet and clinopyroxene could be used to classify rocks into their petrogenetic types.Distribution coefficient calculated by assuming ideal binary solution of Mg and Fe members in pyroxene and garnet is useful to indicate the P-T of the formation of the rocks.  相似文献   

Distribution of elements in coexisting minerals and the problem of chemical disequilibrium in metamorphosed basic rocks     

S. K. Saxena 《Contributions to Mineralogy and Petrology》1969,20(2):177-197

Distribution of elements in coexisting minerals—biotite, hornblende, augite, hypersthene and plagioclase in charnockitic rocks of West Uusimaa Complex, Finland, is mostly orderly indicating a close approach to chemical equilibrium. The distribution of iron and magnesium in coexisting hornblende and pyroxenes of basic charnockites and other rocks of granulite facies from several different areas is also orderly but the variation in the fugacities of H₂O and H₂ may cause a disorderly distribution locally in some rocks. The probable oxidation or reduction reactions are discussed on the basis of thermochemical and mineralchemical data.  相似文献   

Inferring the chemical parameters for the dissolution of fluoride in groundwater   总被引：8，自引：3，他引：8  

V. Saxena  Shakeel Ahmed 《Environmental Geology》2003,43(6):731-736

Geochemical study of groundwater from 58 selected fluoride-rich areas in different parts of India that includes eight states indicates that: 1. These groundwaters are alkaline in pH (7.4-8.8) and their electrical conductivity varies from 530-2,680 µS/cm and fluoride concentration from 1.7-6.1 mg/l. Presence of fluoride-bearing minerals in the host rocks and their interaction with water is considered to be the main cause for fluoride in groundwater. 2. The decomposition, dissociation and dissolution are the main chemical processes for the occurrence of fluoride in groundwater. During rock-water interaction, concentration of fluoride in rock, aqueous ionic species and residence time of interaction, etc. are also important parameters. 3. This study indicates that 85% groundwater samples have EC: 1,000-2,000 µS/cm, pH: 7.5-8.5, and HCO₃/Ca (epm ratio): 0.8-2.3. 4. The Ca and HCO₃ contents of groundwater samples have shown good correlation with fluoride.  相似文献   

Genetic sequence stratigraphy of cool water slope carbonates (Pleistocene Eucla Shelf, southern Australia)     

Sabine Saxena  Christian Betzler 《International Journal of Earth Sciences》2003,92(4):482-493

The south Australian Eucla Shelf belongs to the world's largest cool-water carbonate sedimentary system. During the Pleistocene, it exported large amounts of sediment to the shelf edge and upper slope resulting in an expanded sedimentary wedge. Wedge-internal clinoforming seismic reflectors suggest a stacking of the deposits into genetic sequences. High-resolution stable oxygen and carbon isotope, point counting, grain size, and carbonate mineralogical XRD analyses were carried out to characterize these genetic sequences along a dip-parallel transect of three ODP Leg 182 drill holes located between the shelf edge and upper slope. Oxygen and carbon isotope fluctuations show that the genetic sequences formed as a response to sea level fluctuations. Within the genetic sequences, facies differentiation and sediment volume partitioning occur along the transect. Lowstand deposits are fine grained and contain more sponge spicules and micrite. Highstand deposits are coarse grained with tunicate spicules, brown bioclasts, as well as bryozoan and corallinacean debris. Boundaries separating highstand and lowstand deposits are triggered by sea level fall, and are expressed as abrupt grain size changes or as turning points in grain-size trends. Analyzed components vary in abundance along the transect. Genetic sequences show dip-parallel variations in thickness combined with changing relative proportions of lowstand versus highstand deposits.  相似文献   

Dissolution of fluoride in groundwater: a water-rock interaction study   总被引：4，自引：0，他引：4  

V. Saxena  S. Ahmed 《Environmental Geology》2001,40(9):1084-1087

  相似文献   

Environs of indus and Ganges deltas     

C. S. Harindranath  R. K. Saxena 《Journal of the Indian Society of Remote Sensing》1988,16(4):21-26

Image interpretation coupled with topographical maps and environmental data has led to the conclusion that the web shaped distributaries, west of Kori creek are part of Indus delta system, which has been formed in humid climatic conditions comparable to that of Ganga delta. The present arid climatic conditions in the Indus delta has led to increase in salinity level and is devoid of vegetation. Though morphologically both the Indus and Ganges deltas have similarity but they have vast differences in landuse.  相似文献   

Effects of process variables on the residence time distribution of a solid in a continuously operated flotation cell     

S. P. Mehrotra  A. K. Saxena 《International Journal of Mineral Processing》1983,10(4):255-277

Effects of aeration rate, slurry flow rate, stirring rate, pulp density, and particle size on the residence time distribution of a solid in a continuously operated flotation cell under non-flotation conditions (no frother, no concentrate removal) have been examined. The mixing behaviour of the solid in the cell has been quantitatively analysed using a multiple parameter approach. The results indicate that only a part of the cell volume behaves as a perfect mixer, the remaining being dead. The exit residence time distribution E(t) and the mean residence time ( ) of solid are described by: and where Q is the volumetric slurry flow rate. For the variables ranges examined, it is observed that the aeration does not have any significant effect on the mixing behaviour, V_eff increases with increasing slurry flow rate and stirring rate but decreases with increasing pulp density. The mean residence time, on the other hand, increases with increasing stirring rate, decreases with increasing slurry flow rate and pulp density, and exhibits a maximum with respect to particle size. Following empirical equation correlating the effective volume of the cell with the operating variables for a unisize feed is obtained: where B is the weight fraction of solid in the pulp.  相似文献   

Preparation of optimal land use maps for agricultural development using remote sensing techniques     

R. K. Saxena  R. M. Pofali  L. R. Hirekerur 《Journal of the Indian Society of Remote Sensing》1983,11(3):30-38

Optimal land use map of Kanholi area, part of Nagpur district,Maharashtra have been prepared using Satellite imagery in 1:1000,000 and 1:250,000 and aerial photographs in 1:60,000 scale with adequate ground checks. The Satellite imagery proved valuable information about landscape characteristics, land use, hydrology and other environmental features. The aerial photographs were used to prepare comparatively large scale land resource association maps in scale 1:60,000 on geomorphology, landuse, soil hydrology. Soil irrigability, land irrigability and land capability maps are also attempted after interpreting soils information collected during field studies. The utility of this technique in preparation of optimal land use map with associated limitations due to scale have been discussed in the paper.  相似文献