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Elemental Distribution in the Light Mineral Isolate of Soil Separates¹

ABSTRACT

The light mineral isolate (specific gravity < 2.89) was quantitatively separated from the 50–250µm, 20–50µm, and 5–20µm fractions of selected A and B soil horizons derived from loess and outwash deposits. Elemental Ti, Zr, Fe, K, and Ca were determined by X-ray spectroscopy both on total and light mineral isolates. More than 75% of Ti, Zr, Fe, and Ca occurs in the light mineral isolates of the 5–20µm fraction while the 50–250µm light mineral isolate contains 25 to 70% of these elements. With the exception of K, there is a progressive concentration of above elements as particle-size decreases. Essentially 100% of the K occurs in the light mineral isolate independent of particle-size. The concentration of Ti and Zr is greater than can be accounted for by mineral grain counts in the light isolate. Little or no co-association of Fe with Ti, Zr, Ca, or K could be established in secondary Fe-oxide grain coatings. It is concluded that much of the Ti, Zr, and Fe concentrated in the light mineral isolates occurs as micro-inclusions of accessory minerals within primary host minerals such as quartz and feldspars. Caution must be exercised in allocating elemental percentages of a given size fraction to specific detrital minerals.

¹ Contribution from the Department of Agronomy, Ohio Agricultural Research and Development Center, State Project 371, Journal Paper no. 32-78. Presented before Div. S-9 Soil Sci. Soc. of Am., Miami, Fla., 31 Oct. 1972.

² Research Associate and Professor of Soil and Crop Sciences Department, Texas Agric. Exp. Stn., College Station, TX 77843. respectively. Formerly Instructor and Professor of Agronomy, Ohio Agric. Res. and Dev. Center, Wooster, and Ohio State Univ.

Received for publication August 25, 1977. Accepted for publication July 21, 1978.