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This article in SSSAJ

  1. Vol. 45 No. 2, p. 437-440
    Received: Mar 26, 1980



Identification of Soil Iron Oxide Minerals by Differential X-ray Diffraction1

  1. D. G. Schulze2



If a step-scanned x-ray diffraction pattern of a sample obtained before selective dissolution of all or part of the Fe oxide minerals is substracted from one obtained after dissolution, a differential x-ray diffraction (DXRD) pattern of the Fe oxide fraction that was dissolved can be obtained. After the selective dissolution treatment, the diffraction pattern usually has a greater overall intensity than before, so that all of the points in this pattern must be multiplied by a scale factor less than unity before making the subtraction. With a suitable scale factor, found by trial and error subtractions, a DXRD diagram essentially free of peaks due to minerals other than Fe oxides can be obtained. If DXRD is used, the presence of goethite, hematite, or both can be detected in a sample containing as little as 1.8% Fed (dithionite-citrate-bicarbonate soluble Fe). For samples containing approximately 5% or more Fed, DXRD patterns are suitable for the determination of the goethite/hematite ratio and accurate measurements of peak positions and peak widths. Differential x-ray diffraction clearly showed the material dissolved from a natural sample by oxalate treatment to be ferrihydrite.

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