Browsing by Author "Johnson C.M."
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Browsing by Author "Johnson C.M."
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Barovich K.M.; Beard B.L.; Cappel J.B.; Johnson C.M.; Kyser T.K.; Morgan B.E. (1995)A chemical separation method of Hf from rocks is presented. A procedure involving three stages of ion-exchange columns and sulfuric acid as an eluant produces consistent Zr- and Ti-free Hf separations. The methods described ...
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Beard B.L.; Johnson C.M.; Skulan J.L.; Nealson K.H.; Cox L.; Sun H. (2003)Over 100 high-precision Fe isotope analyses of rocks and minerals are now available, which constrain the range in δ⁵⁶Fe values (per mil deviations in 56Fe/54Fe ratios) in nature from −2.50‰ to +1.5‰. Re-assessment of the ...
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Wiesli R.A.; Beard B.L.; Johnson C.M. (2004)Iron isotope fractionation between aqueous iron and siderite has been measured using abiotic synthesis experiments at ∼20 °C. Applying a Rayleigh distillation model to three experiments in which siderite (FeCO3) was ...
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Beard B.L.; Johnson C.M. (2004)Iron, the fourth most abundant element in the Earth’s crust, has four naturally occurring stable isotopes: 54Fe (5.84%), 56Fe (91.76%), 57Fe (2.12%), and 58Fe (0.28%), and the natural, mass-dependent isotope variations of ...
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Beard B.L.; Johnson C.M. (1999)We present the analytical methods that have been developed for the first high-precision Fe isotope analyses that clearly identify naturally-occurring, mass-dependent isotope fractionation. A double-spike approach is used, ...
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Beard B.L.; Johnson C.M. (2004)Iron isotope and major- and minor-element compositions of coexisting olivine, clinopyroxene, and orthopyroxene from eight spinel peridotite mantle xenoliths; olivine, magnetite, amphibole, and biotite from four andesitic ...
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Beard B.L.; Johnson C.M.; Damm K.L.V.; Poulson R.L. (2003)The Fe isotope composition of Proterozoic to modern clastic sedimentary rocks and aerosols defines a range in 56Fe values that is only slightly more variable than the range of Fe isotope compositions measured in terrestrial ...
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Croal L.R.; Newman D.K.; Johnson C.M.; Beard B.L. (2004)Photoautotrophic bacteria that oxidize ferrous iron (Fe[II]) under anaerobic conditions are thought to be ancient in origin, and the ferric (hydr)oxide mineral products of their metabolism are likely to be preserved in ...
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Johnson C.M.; Beard B.L.; Roden E.E.; Newman D.K.; Nealson K.H. (2004)Cycling of redox-sensitive elements such as Fe is affected by not only ambient Eh-pH conditions, but also by a significant biomass that may derive energy through changes in redox state (e.g., Nealson 1983; Lovely et al. ...
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Johnson C.M.; Skulan J.L.; Beard B.L.; Sun H.; Nealson K.H.; Braterman P.S. (2002)Large equilibrium isotope fractionation occurs between Fe(III) and Fe(II) in very dilute (≤22 mM Cl−) aqueous solutions, reflecting significant differences in bonding environments. Separation of Fe(III) and Fe(II) is ...
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Welch S.A.; Beard B.L.; Johnson C.M.; Braterman P.S. (2003)Equilibrium and kinetic Fe isotope fractionation between aqueous ferrous and ferric species measured over a range of chloride concentrations (0, 11, 110 mM Cl−) and at two temperatures (0 and 22°C) indicate that Fe isotope ...
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Skulan J.L.; Beard B.L.; Johnson C.M. (2002)Application of the Fe isotope system to studies of natural rocks and fluids requires precise knowledge of equilibrium Fe isotope fractionation factors among various aqueous Fe species and minerals. These are difficult to ...
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Wiesli R.A.; Beard B.L.; Taylor L.A.; Johnson C.M. (2003)Nanophase Fe metal grains (np-Fe°) are a product of space weathering, formed by processes related to meteorite impacts, and solar-wind sputtering on airless planetary bodies, such as the Moon. Iron isotopes of lunar soils ...
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Winter B.L.; Johnson C.M.; Clark D.L. (1997)Provenance changes of silicate sediment deposited during the Late Cenozoic (5–0 Ma) on the Alpha Ridge, central Arctic Ocean are determined from variations in strontium, lead, and neodymium isotope compositions. Whereas ...
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Beard B.L.; Taylor L.A.; Scherer E.E.; Johnson C.M.; Snyder G.A. (1998)Five high-Ti basalts from the Apollo 11 and 17 landing sites have been analyzed for their hafnium isotope composition. These data serve to better constrain the hafnium isotope variation of the Moon's mantle. Variations in ...
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Jicha B.R.; Singer B.S.; Brophy J.G.; Fournelle J.H.; Johnson C.M.; Beard B.L.; Lapen T.J.; Mahlen N.J. (2004)Major and trace element compositions and Sr, Nd, Pb, and Hf isotope ratios of Aleutian island arc lavas from Kanaga, Roundhead, Seguam, and Shishaldin volcanoes provide constraints on the composition and origin of the ...
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