Forest Preserve District of Cook County, Illinois
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Silica Sand
Nature Bulletin No. 587   January 16, 1960
Forest Preserve District of Cook County
Daniel Ryan, President
Roberts Mann, Conservation Editor
David H. Thompson, Senior Naturalist

"I'm from Illinois." No matter where we go, those of us born and raised here can say those three words with justifiable pride. Illinois stands at the top or near the top, among the 50 states, in all of the five great occupations of mankind: agriculture, mining, manufacturing, transportation and trade. Richly endowed with natural resources, a beneficent and invigorating climate, and plenty of rainfall, Illinois occupies a strategic central location at the south end of Lake Michigan and in the heart of the Corn Belt -- the breadbasket of America.

In addition to its fabulous black prairie soils, this state is also rich in mineral wealth. It has no ore deposits of iron, copper, gold or silver, but it has great oil fields, and workable beds of coal underlie about two- thirds of its total area. Mines, oil or gas wells, stone quarries, clay pits, and gravel or sand pits are located in at least 100 of the 102 counties. In the nation, Illinois ranks fifth as a producer of minerals and mineral products. It ranks first in the production of two vital materials: fluorspar -- mined in Pope and Hardin counties along the Ohio river -- and, at Ottawa in LaSalle county, Silica Sand.

Ottawa silica sand is unique. Its rounded grains of clear colorless quartz, diamond-like in hardness, are pure silica (silicon dioxide) uncontaminated by clay, loam, iron compounds, or other foreign substances. It is obtained from the St. Peter sandstone, a massive formation from 140 to 275 feet in thickness, that outcrops along the Illinois and the Fox rivers near Ottawa.

On the outskirts of that city, where the Ottawa Silica Sand Co. quarries and processes this material, the top of the sandstone is only a few feet below the surface; 10 miles east it dips downward about 800 feet. Downstream between Ottawa and Utica, Starved Rock and Buffalo Rock (also a state park) and Split Rock are isolated masses of St. Peter sandstone which became detached from the bluffs by erosion and rise like towering fortresses above the valley floor.

Silica sand is also obtained from quarries at Streator and near Alton in Illinois; along the Huron river at Rockwood, Michigan; in Minnesota, Connecticut and elsewhere; but the St. Peter sandstone at Ottawa produces the purest and the best, carefully screened into uniform sizes for various industrial uses.

Glass is made from silica sand. The purer the sand, the clearer the glass. Any impurities, especially traces of iron compounds, discolor it. Ottawa silica sand is shipped to glass manufacturers in many parts of the United States and the Libbey-Owens-Ford Glass Co. has a big plant at Ottawa where they manufacture plate glass wind shields and windows for automobiles.

Silica sands with uniform grains of specified size must be used for the molds and cores in foundries that make steel castings, and for casting gray iron, brass, aluminum and magnesium metals. Since silica sand has a very high melting point, it is used in the manufacture of fire brick and to line the bottoms of furnaces making malleable iron. Because of its extreme hardness, there are many other industrial uses such as for sand blasting castings and the inscriptions on monuments; for sawing stone or marble with sand and water; for sandpaper and for abrasives used in grinding and polishing.

The filter beds in water purification plants are filled with Ottawa silica sand. Many years ago it was chosen by the American Society for Testing Materials as the standard sand to be used in testing cement and the strength of concrete.

This humble mineral from Illinois has vast importance.

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