Glaciated pebbles can be found in deposits in many parts of the state, especially in northeastern and east-central Illinois. However, many deposits near the surface have been weathered and striae have been destroyed. An especially good place to look for striated pebbles is in quarries and strip mines where glacial drift overburden has been removed. Pebbles found in such deposits show good striae for they are but little weathered.
SILICA SAND (17)
SILICA SAND is the commercial name for sand composed almost entirely of grains of quartz. Sand of this kind is mined in Illinois from the St. Peter Sandstone in LaSalle and Ogle Counties. The coarser grains of the sand are characteristically rounded and frosted. The frosting causes the sand to look white.
Illinois silica sand has many uses. It is used just as it is mined for molding sand in which metal castings are made, for lining industrial furnaces, and for many other purposes. Some of the sand is washed to remove the small amount of impurities present. The washed sand is used for such purposes as making glass, for grinding plate glass smooth, for sand blasting, for molding metal, as fracturing sand to increase the production of oil wells. Some silica sand is ground to a fine powder and used as a fine abrasive, as a filler in paint, and as an ingredient in pottery, glazes, and enamel.
A specially prepared St. Peter sand, known throughout the world as Standard Ottawa Testing Sand, is used to test the strength of cements and as a laboratory standard in physical tests of other sands.
MOLDING SAND (18)
MOLDING SAND is a mixture of sand and clay or other bonding material and is used to make molds in which metal is cast into various useful shapes. There are two kinds of molding sands, synthetic and natural bonded. The first is an artificial mixture of silica sand and clay; the second is a naturally occurring mixture of sand and a bonding material.
For casting, molding sand is first moistened with water and shaped into a mold of the metal part to be reproduced. The mold is then allowed to dry and the molten metal poured into it. The bonding material in the sand must be strong enough to keep the mold in shape during these operations.
Natural bonded molding sand is produced in Fayette, Bond, Bureau, Carroll, Kankakee, and Rock Island Counties, Illinois.