Solid Mineral Phases Research Articles

Electron diffraction and electron probe microanalysis of the mineral phase of bone tissue prepared by anhydrous techniques

Selected area electron diffraction and high spatial resolution, nondispersive electron probe Xray microanalysis have been used to examine the nature of the solid phase mineral deposits of specific ultrastructural components in freshly dissected, undecalcified bone tissue from embryonic chicks, prepared anhydrously with either 100% ethylene glycol or dry ultracryomicrotomy. No electron diffraction patterns of a specific calcium phosphate solid phase are generated from the dense mitochondrial granules of osteoblasts, shown to contain calcium and phosphorus by electron probe microanalysis, and from the early mineral deposits from certain regions of newly synthesized bone. Similar results are obtained from a synthetic preparation of an amorphous calcium phosphate. Absence of an electron diffraction pattern is not caused by an insufficient mass of the calcium phosphate solid phase. The electron diffraction patterns of the more heavily mineralized older regions of the bone show the reflections and characteristics of poorly crystalline hydroxyapatite. There is a progressive change in the electron diffraction pattern approaching that of crystalline hydroxyapatite with increasing distance from the periosteal surface. Electron probe microanalysis of the same tissue components and regions shows that the changes in the electron diffraction characteristics are accompanied by an increase in the Ca/P ratios of the solid mineral phase.

Chemical weathering on Mars thermodynamic stabilities of primary minerals (and their alteration products) from mafic igneous rocks

Chemical weathering on Mars is examined theoretically from the standpoint of heterogeneous equilibrium between solid mineral phases and gaseous O 2, H 2O, and CO 2 in the Martian atmosphere. Thermochemical calculations are performed in order to identify important gas-solid decomposition reactions involving the major mineral constituents of mafic igneous rocks. Where unavailable in the thermochemical literature, Gibbs free energy and enthalpy of formation are estimated for certain minerals and details of these estimation procedures are given. Partial pressure stability diagrams are presented to show pertinent mineral reaction boundaries at 298 and at 240°K. In the present Martian environment, the thermodynamically stable products of gas-solid weathering of individual minerals at 240°K should be Fe 2O 3, as hematite or maghemite (from fayalite, magnetite, and Fe-bearing pyroxenes), quartz (from all silicates), calcite (from Ca-bearing pyroxenes and plagioclase), magnesite (from forsterite and Mg-bearing pyroxenes), corundum (from all Al-bearing silicates), Ca-beidellite (from anorthite), and szomolnokite, FeSO 4 or FeSO 4·H 2O (from iron sulfides). Albite, microcline, and apatite should be stable with respect to gas-solid decomposition, suggesting that gas-solid weathering products on Mars may be depleted in Na, K, and P (and, possibly, Cl and F). Certain montmorillonite-type clay minerals are thermodynamically favorable intermediate gas-solid decomposition products of Al-bearing pyroxenes and may be metastable intermediate products of special mineral surface reaction mechanisms. However, the predicted high thermodynamic susceptibility of these clay minerals to subsequent gas-solid decomposition implies that they should ultimately decompose in the present Martian surface environment. Kaolinite is apparently the only clay mineral which should be thermodynamically stable over all ranges of temperature and water vapor abundance in the present environment at the Martian surface. Considering thermodynamic criteria, including possible gas-solid decomposition reactions, it is doubtful that significant amounts of goethite and clay minerals can be currently forming on Mars by mechanisms known to operate to Earth. If major amounts of goethite and clay minerals occur on Mars, they probably owe their existence to formation in an environment characterized by the presence of liquid water or by mechanism possibly unique to Mars. In any case, any goethite or montmorillonite-type clay mineral on Mars must ultimately decompose.

DISTRIBUTION OF TRACE METALS IN THE PORE WATERS OF SHALLOW WATER MARINE SEDIMENTS

The concentrations of seven trace metals in the pore waters of marine sediments from Loch Fyne, Scotland, have been analyzed by atomic absorption spectrophotometry following solvent extraction. The samples were taken from sediments containing variable amounts of sulfide at depth and variable thicknesses of oxides at the surfaces; one core contains abundant manganese nodules and manganese‐calcium carbonate concretions.The distribution of dissolved Mn shows a regular downward decrease in all cores examined which is interpreted as an indication of recycling of Mn between solid diagenetic mineral phases and pore solutions. Dissolved Fe, in much lower concentrations, either decreases or increases down the core depending on the type of sediment; Cu, Ni, Zn, Co, and Pb also show variable concentration profiles indicating control by different post‐depositional reactions in the sediment, which in turn depend on different physiochemical environments generated by variable amounts of contained organic material and different accumulation rates.

Influence of the soil matrix on the availability of trace elements to plants.

Soils play a vital role in determining the availability of trace elements to plants. The uptake of trace elements by plants constitutes an important link in the food chain of man. There are two important parameters in soils that influence the availability of an element to plants. One of these is the intensity factor or the concentration of an element in the soil solution. The other is the capacity factor or the ability of the solid phases of soils to replenish an element as it is depleted from solution. In soils, trace elements are present in several forms including ions in solution, adsorbed ions, solid phase minerals, and soil organic matter. Recently an extractant was developed for the simultaneous determination of available Zn, Fe, Mn, and Cu in soils. 10 references, 3 figures, 1 table.

CHEMICAL EQUILIBRIUM DIAGRAMS FOR GROUND-WATER SYSTEMS / Les graphiques de l'équilibre chimique pour les systèmes des eaux souterrainnes

Abstract Chemical equilibrium in water in contact with calcite is expressed by means of a pH grid overlay on a log-log plot of activities of bicarbonate vs. calcium ions. Solubility of ferrous iron and the solid-phase minerals that would be stable in a solution containing activities of 10 ppm of sulfate and 100 ppm of bicarbonate or related species is expressed by means of a stability-field diagram with pH as abscissa and redox potential as ordinate. The diagrams can be used to tell whether water injected in recharge wells may form precipitates that may plug the aquifer and have other uses in studies of natural water chemistry.