Geology topics
Publications and source records attributed to J. M. Axelrod.
An x-ray spectrographic method for the determination of rubidium and cesium was developed, using the internal-standard method and a four-channel flat-crystal spectrograph. The sensitivity is within 0.1% for cesia and 0.02% for rubidia; the precision is within 10% of the amount present. Results agree well with those obtained by flame photometry and by radio-activation.
A curved-crystal reflecting spectrometer of the type described by Birks and Brooks of the Naval Research Laboratories, but adapted for use in mineralogical studies, has been built in the Geological Survey. It has been successfully applied to the analysis of tiny crystals, zones in minerals, and individual grains in mixed-mineral specimens such as thin or polished sections, on grains or areas about 0.5 mm in diameter, X-ray diffraction spindles, and small samples of powder weighing a fraction of a milligram have also been analyzed without any loss or alteration of the sample. Of great value in thin- and polished-section work is the fact that this technique can be used to analyze selected areas without mutilating the specimen by digging out grains.A modification of the curved-crystal spectrometer has made it possible to traverse a standard polished section in synchronization with a recorder, automatically plotting the distribution of various elements along a selected line. This method was applied, for example, to a polished section containing a central core of pyrite intergrown with and surrounded by a marcasite-like mineral. Chemical analysis of a concentrate of these two minerals gave selenium, cobalt, and iron as major constituents. A clear relationship between the cobalt, selenium, and iron was established by the X-ray method, identifying the second mineral as an intermediate member of the FeSe 2 -CoSe 2 series.
The use of internal standards in the analysis of ores and minerals of widely-varying matrix by means of fluorescent X-ray spectroscopy is frequently the most practical approach. Internal standards correct for absorption and enhancement effects except when an absorption edge falls between the comparison lines or a very strong emission line falls between the absorption edges responsible for the comparison lines. Particle size variations may introduce substantial errors. One method of coping with the particle size problem is grinding the sample with an added abrasive.
A fluorescent x-ray spectrographic method for the determination of thoria in rock samples uses thallium as an internal standard. Measurements are made with a two-channel spectrometer equipped with quartz (d = 1.817 A.) analyzing crystals. Particle-size effects are minimized by grinding the sample components with a mixture of silicon carbide and aluminum and then briquetting. Analyses of 17 samples showed that for the 16 samples containing over 0.7% thoria the average error, based on chemical results, is 4.7% and the maximum error, 9.5%. Because of limitations of instrumentation, 0.2% thoria is considered the lower limit of detection. An analysis can be made in about an hour.
[No abstract available]
Iron phosphate minerals which cement talus ore below cliffs formed by massive magnetite- hematite deposits at Bomi hill, Liberia, and also occur in place in fissures and caves in the ore both at Bomi hill and Bambuta, were formed by the interaction of bat dung and iron oxides. The minerals include leucophosphite (previously known only from Western Australia), phosphosiderite, and strengite. Analyses of the leucophosphite are included.
No abstract available.
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