Excerpt from Feldspar in Illinois Sands: A Further Study

The sands studied are of Pleistocene age, and all were derived at least in part from glacial material The sands are of three types: dune, river, and beach. The dune sands are found mainly in northern and central Illinois The largest deposits of river sand occur in the Mississippi, Illinois, Wabash, and Ohio Rivers. The beach sands occur along Lake Michigan and in the area covered by Glacial Lake Chicago. The glacial outwash of Illinois also contains much sand, but this sand is generally rather coarse-grained and associated with gravel. Be cause coarse sand is generally less desirable as a source of feldspar than fine or medium-grained sand due to its lower feldspar content, the glacial outwash sands were not included in the present study.

The dune sands are largely light brown in color because of an iron oxide coating on the grains. The sand in the lower parts of the dunes is less weathered and contains less iron oxide than that in the upper parts Much of the dune sand is noncalcareous, but the lower parts of some dunes contain limestone and dolomite grains The dominant size fraction varies from the 35 by 48-mesh fraction to the 65 by loo-mesh fraction in different dune sands (willman, 1942, p. Most of the dune sands contain less than 5 percent silt and clay.

The river sands are lighter gray in color than the dune sands The sands of the Illinois and Wabash Rivers contain many limestone and dolomite grains.

The sands of the Ohio and Mississippi Rivers contain lesser amounts of such grains, and some samples studied by Willman (1942, p. 20) contain no carbonate. With the exception of the Mississippi River sands south of Alton, few of the river sands sampled by Willman are as fine-grained as the fine-grained dune sands. In the Mississippi River south of Alton, large sand deposits occur in which the dominant size fraction is 65 by loo-mesh.

The beach sands are similar to the river sands in color and contain large amounts of limestone and dolomite grains. They range from pebbly sands to sands similar to the dune sands in grain size (willman, 1942, p.23).

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