STATE of ILLINOIS
William G. Stratton, Governor

DEPARTMENT of
REGISTRATION and EDUCATION
Vera M. Binks, Director

First printing 1959
Second printing 1960

ILLINOIS STATE GEOLOGICAL SURVEY
John C. Frye, Chief
URBANA, ILLINOIS

Printed by Authority of the State of Illinois

Guide to ROCKS AND MINERALS OF ILLINOIS

Illinois has so long been known as the Prairie State thatat first glance it seems a most unlikely place in which tocollect rock and mineral specimens.

But Illinois has a surprising wealth of rock and mineral resources,not only to be collected as interesting specimens butto be put to practical and profitable use.

The rich prairies that gave the state its nickname are themselvesderived from ancient rocks, worn and changed by millionsof years of action by weather, water, wind, plants, and animals.Unmeasured depths of rock underlie the prairies, hills, and valleys,and in some parts of the state are exposed in outcrops,canyons, and river valleys. Boulders and gravel brought in bythe glaciers thousands of years ago are strewn over many partsof the state.

These resources are of great value. Besides the rich agriculturebased on the rock-derived soil, much of our industry,manufacturing, and transportation is dependent on rock and mineralmaterials. Every county in Illinois possesses some rocksand minerals that either are being used or have potential futurevalue.

The Illinois State Geological Survey several years ago beganto prepare sets of typical rocks and minerals of Illinois foruse by the schools and other educational groups in Illinois.This booklet is designed to furnish a brief geological backgroundand explanation of these common Illinois rocks and minerals.It also should be useful to the student or amateur interested inmaking his own collection.

Even though Illinois has no mountain ranges or deep canyons,the geology of the state has many complexities. In fact,the very flatness of our topography is a complicating factor becausein order to study the geology at many places in the stateit is necessary to use information from mines and descriptions(logs) and samples (cores) of the rock penetrated during drillingof deep wells. There are also geophysical methods of learningsomething about the rocks beneath the surface.

Fig. 1.—Geologic map of Illinois.

CAMBRIAN

ORDOVICIAN

ORDOVICIAN-SILURIAN

ORDOVICIAN-SILURIAN UNDER DRIFT

DEVONIAN-MISSISSIPPIAN

PENNSYLVANIAN UNDER DRIFT

CRETACEOUS-TERTIARY

KEY

Wisconsin glacial drift

Illinoian glacial drift

Penn

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