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Characterization of Iron Oxide Minerals by Second-Derivative Visible Spectroscopy¹

ABSTRACT

Derivative spectroscopy is a technique of calculating and plotting the first, second, or higher order derivative of the spectral curve relating absorption and wavelength. The second derivative greatly enhances minor convexities and concavities of the original (zero order) spectrum and gives a much narrower band width which provides improved resolution of subtle or overlapping bands. The visible spectrum and its second derivative were determined for natural and synthetic goethite and synthetic hematite. The two minerals have distinctive second-derivative patterns. The minimum at 423 nm and the maximum at 447 nm in the second-derivative patterns were used to estimate the amount of goethite in a mixture with kaolinite. Whole soil samples can be analyzed without pretreatment by this method, assuring that the result of the analysis is a property of the soil itself and not an artifact of a pretreatment.

¹ Contribution from the Agron. Dep., Purdue Univ. Agric. Exp. Stn., West Lafayette, IN 47907. Journal Paper no. 9487.

² Graduate Fellow (NATO program); former Graduate Fellow (MEC/CAPES program), now Associate Prof., Escola Superior de Agricultura de Lavras, Minas Gerais State, Brazil; Former Instructor, now Assistant Prof., Agron. Dep., Cornell Univ.; and Professor, respectively.

Received for publication May 31, 1983. Accepted for publication September 29, 1983.

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