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# Iron-Stained Sands and Clays

G. R. MacCarthy
The Journal of Geology
Vol. 34, No. 4 (May - Jun., 1926), pp. 352-360
Stable URL: http://www.jstor.org/stable/30063686
Page Count: 9
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## Abstract

It is pointed out that the distribution of color in a sediment is as important in determining the general color effect as is the total amount of coloring matter present. It is shown that quartz will become iron-stained only in the absence of more active adsorbants, that orthoclase acquires iron stain more readily than quartz, and that while A1(OH)₃ is a good adsorbant of iron, pure kaolin will adsorb but little unless activated by some such substance as the alkali carbonates. The iron content of clays up to about 5.0 per cent Fe₂O₃ is shown to be a linear function of the alkali content, the equation $A=\frac{10 B-4}{7}$ where A = percentage of Fe₂O₃ present and B = percentage of Na₂O+K₂O present holds true for averages of several analyses, but not for individual clays, within these limits. It is suggested that the deep red color developed by so many tropical soils is a result of the retention of iron by the hydroxides which occur plentifully in such soils.

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