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Featured researches published by Priestley Toulmin.


Geochimica et Cosmochimica Acta | 1964

A thermodynamic study of pyrite and pyrrhotite

Priestley Toulmin; Paul B. Barton

Abstract Through the use of the electrum-tarnish method the following equation has been found to interrelate the composition of pyrrhotite, fugacity of sulfur, and temperature: In this equation fs2 is the fugacity of sulfur relative to the ideal diatomic gas at 1 atm, N is the mol fraction of FeS in pyrrhotite (in the system FeS-S2), and T the absolute temperature. The experimental uncertainty in the equation is 0–003 in N. The activity of FeS (aFeS) in pyrrhotite relative to the pure substance at the temperature of consideration follows from the above equation by virtue of the Gibbs-Duhem relation; it is given by: The electrum-tarnish method has permitted us to determine the fs2 vs. T curve for the univariant assemblage pyrrhotite-pyrite-vapor from 743 to 325°C. Our determinations of the composition of pyrrhotite are in excellent agreement with the results of Arnold. The activity of FeS in pyrite-saturated pyrrhotite is very different from unity, a fact that greatly influences the interpretation of some other phase equilibrium studies involving pyrrhotite and their application to sulfide mineral assemblages, but has little effect on the more general calculations of composition of hydrothermal or magmatic fluids. Pressure effects calculated from available volumetric data on the phases are small.


Science | 1976

Search for organic and volatile inorganic compounds in two surface samples from the Chryse Planitia region of Mars

K. Biemann; J. Oró; Priestley Toulmin; Leslie E. Orgel; Alfred O. Nier; D.M. Anderson; Peter G. Simmonds; Donald A. Flory; A.V. Diaz; D.R. Rushneck; J.A. Biller

Two surface samples collected from the Chryse Planitia region of Mars were heated to temperatures up to 500�C, and the volatiles that they evolved were analyzed with a gas chromatograph-mass spectrometer. Only water and carbon dioxide were detected. This implies that organic compounds have not accumulated to the extent that individual components could be detected at levels of a few parts in 109 by weight in our samples. Proposed mechanisms for the accumulation and destruction of organic compounds are discussed in the light of this limit.


Science | 1976

Inorganic analyses of Martian surface samples at the Viking landing sites

Benton C. Clark; A. K. Baird; Harry J. Rose; Priestley Toulmin; Klaus Keil; Angelo J. Castro; Warren C. Kelliher; Catherine D. Rowe; Peter H. Evans

Elemental analyses of fines in the Martian regolith at two widely separated landing sites, Chryse Planitia and Utopia Planitia, produced remarkably similar results. At both sites, the uppermost regolith contains abundant Si and Fe, with significant concentrations of Mg, Al, S, Ca, and Ti. The S concentration is one to two orders of magnitude higher, and K(<0.25 percent by weight) is at least 5 times lower than the average for the earths crust. The trace elements Sr, Y, and possibly Zr, have been detected at concentrations near or below 100 parts per million. Pebblesized fragments sampled at Chryse contain more S than the bulk fines, and are thought to be pieces of a sulfate-cemented duricrust.


Science | 1976

Mineralogic and Petrologic Implications of Viking Geochemical Results From Mars: Interim Report

A. K. Baird; Priestley Toulmin; Benton C. Clark; Harry J. Rose; Klaus Keil; Ralph P. Christian; James L. Gooding

Chemical results from four samples of martian fines delivered to Viking landers 1 and 2 are remarkably similar in that they all have high iron; moderate magnesium, calcium, and sulfur; low aluminum; and apparently very low alkalies and trace elements. This composition is best interpreted as representing the weathering products of mafic igneous rocks. A mineralogic model, derived from computer mixing studies and laboratory analog preparations, suggests that Mars fines could be an intimate mixture of about 80 percent iron-rich clay, about 10 percent magnesium sulfate (kieserite?), about 5 percent carbonate (calcite), and about 5 percent iron oxides (hematite, magnetite, maghemite, goethite?). The mafic nature of the present fines (distributed globally) and their probable source rocks seems to preclude large-scale planetary differentiation of a terrestrial nature.


Geochimica et Cosmochimica Acta | 1964

The electrum-tarnish method for the determination of the fugacity of sulfur in laboratory sulfide systems

Paul B. Barton; Priestley Toulmin

A new method for the determination of the fugacity of sulfur in laboratory systems consists of visual observation of the development and decomposition of a sulfide tarnish phase on silver-gold alloy (electrum) of precisely known composition. The alloy system is calibrated against pure sulfur. The method has the following advantages: simple apparatus; ability to cover a large range of fugacity of S2; ability to cover a large temperature range by permitting runs of long duration; ability to tolerate other components in the gas phase; and ease of recovery of the quenched charges for determinations of phases and compositions. Results obtained by the electrum-tarnish method are in satisfactory agreement with those obtained by other workers for the fs2 vs. T curves for the assemblage Ni(1–x)S + NiS2. The electrum-tarnish method shows promise for investigating many other reactions. Univariant reactions studied by this method can be represented as lines forming a genetic grid in terms of the environmental parameters fs2 and T, The slopes of such lines can yield valuable thermodynamic data for the phases involved, but activity coefficients must be known for phases of variable composition.


Icarus | 1972

Mass spectrometric analysis of organic compounds, water and volatile constituents in the atmosphere and surface of Mars: The Viking Mars Lander

Duwayne M. Anderson; K. Biemann; Leslie E. Orgel; J. Oró; Tobias Owen; Garson P. Shulman; Priestley Toulmin; Harold C. Urey

Abstract An experiment centering around a mass spectrometer is described, which is aimed at the identification of organic substances present in the top 10 cm of the surface of Mars and an analysis of the atmosphere for major and minor constituents as well as isotopic abundances. In addition, an indication of the abundance of water in the surface and some information concerning the mineralogy can be obtained by monitoring the gases produced upon heating the soil sample. The organic material will simply be expelled by heating to 150°, 300°, and 500° into the carrier gas stream of a gas chromatograph interfaced to the mass spectrometer or by slowly heating the sample in direct communication with the spectrometer. It is planned to analyze a total of up to nine soil samples in order to study diurnal and seasonal variations. The system is designed to give useful data even for minor constituents if the total of organics should be as low as 5ppm. The spectrometer covers the mass range of 12–200 with adequate resolution. The results of these experiments, which are deliberately designed to cover a wide spectrum of possibilities independent of terrestrial models, are expected to produce a good picture of the planets organic chemistry and its possible biological significance as well as allow conclusions regarding the history of the planets atmosphere.


Science | 1976

Preliminary results from the viking x-ray fluorescence experiment: The first sample from chryse planitia, Mars

Priestley Toulmin; Benton C. Clark; A. K. Baird; Klaus Keil; Harry J. Rose

Iron, calcium, aluminum, silicon, and sulfur are major elements in the first surface sample of Mars that has been analyzed by the Viking x-ray fluorescence spectrometer. Titanium is present in minor quantities. This is consistent with the sample being a mixture of fine silicate and oxide mineral grains, with a significant proportion of sulfates, possibly hydrated. Ferric oxide is regarded as the red pigmenting agent on the martian surface, but if it coats silicate grains, the coatings must be very thin (≤ 2 micrometers) or discontinuous. A high abundance of Fe, relatively low abundances of Al, Rb, Sr, and Zr, and a high Ca/K ratio are distinctive features of the spectra. Preliminary determinations indicate the following abundances (as percentages by weight): Fe, 14 � 2; Ti < 1; S, 2 to 5; the Ca/K ratio by weight is greater than 5.


Icarus | 1973

Inorganic chemical investigation by X-ray fluorescence analysis - The Viking Mars Lander

Priestley Toulmin; A. K. Baird; Benton C. Clark; Klaus Keil; Harry J. Rose

Abstract The inorganic chemical investigation added in August 1972 to the Viking Lander scientific package will utilize an energy-dispersive X-ray fluorescence spectrometer in which four sealed, gas-filled proportional counters will detect X-rays emitted from samples of the Martian surface materials irradiated by X-rays from radioisotope sources ( 55 Fe and 109 Cd). The output of the proportional counters will be subjected to pulse-height analysis by an on-board step-scanning single-channel analyzer with adjustable counting periods. The data will be returned to Earth, via the Viking Orbiter relay system, and the spectra constructed, calibrated, and interpreted here. The instrument is inside the Lander body, and samples are to be delivered to it by the Viking Lander Surface Sampler. Calibration standards are an integral part of the instrument. The results of the investigation will characterize the surface materials of Mars as to elemental composition with accuracies ranging from a few tens of parts per million (at the trace-element level) to a few percent (for major elements) depending on the element in question. Elements of atomic number 11 or less are determined only as a group, though useful estimates of their individual abundances maybe achieved by indirect means. The expected radiation environment will not seriously hamper the measurements. Based on the results, inferences can be drawn regarding (1) the surface mineralogy and lithology; (2) the nature of weathering processes, past and present, and the question of equilibrium between the atmosphere and the surface; and (3) the extent and type of differentiation that the planet has undergone. The Inorganic Chemical Investigation supports and is supported by most other Viking Science investigations.


Economic Geology | 1973

Thermochemistry of ore minerals and its application

A. J. Naldrett; Priestley Toulmin

Proceedings of symposium, Montreal, Quebec, 1972 (includes preface by Naldrett and Toulmin and 8 papers, cited in this Bibliography under the separate authors)


Journal of Geophysical Research | 1977

The search for organic substances and inorganic volatile compounds in the surface of Mars

Klaus Biemann; J. Oro; Priestley Toulmin; Leslie E. Orgel; Alfred O. Nier; D. M. Anderson; Peter G. Simmonds; D. Flory; A. V. Diaz; D. R. Rushneck; J. E. Biller; A. L. Lafleur

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Klaus Keil

University of Hawaii at Manoa

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Harry J. Rose

United States Geological Survey

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Leslie E. Orgel

Salk Institute for Biological Studies

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Paul B. Barton

United States Geological Survey

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J. Oró

University of Houston

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K. Biemann

Massachusetts Institute of Technology

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