Part 1

INDUSTRIAL MINERALS AND METALS OF ILLINOIS

J. E. Lamar

Illinois State Geological Survey Educational Series 8

STATE of ILLINOIS

1965

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

Printed by Authority of State of Illinois, Ch. 127, IRS, Par. 58.25.

(15M-4/65-8976) 10

INDUSTRIAL MINERALS AND METALS OF ILLINOIS

J. E. Lamar

The mineral resources of Illinois include many rocks and minerals of varied character and uses. From them are made an array of everyday products whose sources may not even be recognized by the consumer. The user of a glass bottle, for instance, rarely knows that it may have been made from Illinois silica sand, nor is the driver of an automobile generally aware that the Illinois concrete highway on which he is driving probably was constructed from a mixture of cement, sand and gravel, or crushed stone that may have come from Illinois pits or quarries.

The significance of these rocks and minerals to the economy of Illinois is great, although often unappreciated. Of the more than 600 million dollar value of all Illinois mineral production in 1963, almost 200 million was from industrial minerals. The diversity and widespread distribution of these mineral resources lend variety and balance to the mineral industry of the state, and their production, processing, and utilization afford direct and indirect employment to many people.

The term industrial minerals is used as a convenient group term for nonmetallic minerals that are not fuels. In Illinois they include limestone, dolomite, clay, shale, silica sand and other sands, fluorspar, tripoli (amorphous silica), ganister, novaculite, sandstone, feldspar-bearing sands, barite, gypsum, anhydrite, brines, greensand, oil shale, marl, peat, humus, and tufa. The metallic minerals of Illinois are galena (lead ore), sphalerite (zinc ore), pyrite, and marcasite.

This booklet briefly and nontechnically discusses the foregoing materials and some of the work the Illinois State Geological Survey does in gathering information about their occurrence, and character and in developing new uses.

The assistance of many Survey staff members and of many people in the Illinois mineral industry in the preparation of this booklet is acknowledged.

LIMESTONE

Limestone is a most versatile rock. Without it there would be no portland cement for making concrete roads and buildings, no lime for plastering and chemical use, no agricultural limestone for farms, and no crushed limestone for driveways. A wide variety of industries, from steel making to glass manufacturing, use limestone in one way or another.

The early settlers of Illinois recognized the value of limestone and quarried stone blocks and slabs for making foundations, chimneys, and even houses. For mortar they used a mixture of sand and lime to hold the blocks together. The lime was made by heating limestone red hot in simple furnaces or kilns, the ruins of a few of which may still be seen.

Kinds of Limestone

Illinois has two principal varieties of limestone, referred to technically as limestone and dolomite. “Limestone” may be used as a general name for both varieties.

Limestone consists principally of crystalline particles of the mineral calcite (fig. 1). This mineral is glassy in appearance and is composed of calcium, carbon, and oxygen combined to form calcium carbonate—CaCO₃. Dolomite is largely made of crystalline particles of the mineral dolomite, which also has a glassy appearance and consists of calcium, magnesium, carbon, and oxygen—CaMg(CO₃)₂. The crystalline particles of limestone and dolomite vary in size. Some are coarse enough to be seen easily, others are so small that they can be distinguished only with a microscope.

Formation of Limestone and Dolomite

Almost all Illinois limestones were formed in seas that covered Illinois millions of years ago. The many different limestone formations in Illinois suggest that oceans covered all or part of the area several times. Numerous kinds of shell fish, corals, and other marine animals lived in these oceans and had shells and other hard parts made of calcium carbonate. Through countless generations, these animal remains accumulated on the ocean floor and gradually were compacted and cemented into limestone (fig. 2).

Other Illinois limestones, however, were formed by the hardening of muds composed mainly of calcium carbonate that accumulated on the floors of the ancient seas. Still other limestones were formed of a combination of animal remains and lime mud.

The coral reefs of the South Pacific Ocean have their counterparts in Illinois. The ancient Illinois oceans contained extensive reefs that were built up just as the modern reefs have been. In northern Illinois, around Chicago for instance, a number of the ancient reefs are now the site of stone quarries. In southwestern Illinois such reefs are a source of petroleum.

The dolomites of Illinois probably were originally limestones, but, either while the limestones were still beneath the sea or after the sea had withdrawn, magnesium was exchanged for some of the calcium in the limestones. If the exchange took place under the sea, the sea water was the source of the magnesium. If it happened when the limestones were a part of the land, the magnesium was brought in by water circulating through the rock. Many of the marine animal fossils became difficult to recognize after the change, and the texture and general appearance of the rock also were altered. Some of it became noticeably porous.

Uses of Limestone and Dolomite

Some of the major uses for Illinois limestone and dolomite are mentioned below. Not every limestone or dolomite can be used for all purposes because for each use the stone must fulfill special requirements of a chemical or physical nature. For example, it must have high purity for lime, resistance to wear and weather for roads and buildings, and a pleasing appearance for decorative stone and marble.