3 The Project Gutenberg eBook of Industrial Minerals and Metals of Illinois, by J. E. Lamar This eBook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at www.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook. Title:Industrial Minerals and Metals of Illinois Educational Series 8 Author: J. E. Lamar Release Date: May 23, 2021 [eBook #65426] Language: English Character set encoding: UTF-8 Produced by: Stephen Hutcheson and the Online Distributed Proofreading Team at https://www.pgdp.net *** START OF THE PROJECT GUTENBERG EBOOK INDUSTRIAL MINERALS AND METALS OF ILLINOIS *** Industrial Minerals and Metals of Illinois INDUSTRIAL MINERALS AND METALS OF ILLINOIS J. E. Lamar Illinois State Geological Survey Educational Series 8 STATE of ILLINOIS DEPARTMENT of REGISTRATION and EDUCATION 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 4 5 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. Figure 1—Calcite crystals. Limestone is made up mainly of calcite crystals, but they are less perfectly formed and are crowded together. 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 9 6 7 8 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. Figure 2—Limestone containing fossils. An Archimedes screw appears at lower left, lace-like bryozoa in the center, and fluted brachiopod shells at top and center. 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. Lime.—When limestone or dolomite is heated to a high temperature, it undergoes a change and carbon dioxide is liberated. The weight of the gas set free is equal to somewhat less than half the weight of the rock if the rock is pure. The solid product remaining after the gas has been driven off is known as lime. The heating process is called burning. Besides being used in making mortar and plaster, lime is valuable in many other ways, especially in various chemical processes of modern industry. Plants at Chicago and Quincy make lime from Illinois limestone and dolomite. Figure 3—An Illinois dolomite quarry. Cement.—Portland cement, sometimes called simply cement, is made at LaSalle, Oglesby, and Dixon in northern Illinois from limestone and a smaller, carefully measured amount of clay or shale. Cement also is made at Joppa in southern Illinois. The blend of materials is thoroughly ground and mixed, then heated at a high temperature in huge rotating horizontal furnaces, called kilns, until it forms a clinker. After it cools, the clinker is ground to a flourlike powder. This is basically the cement that binds together the mixture of sand and limestone (or dolomite), or of sand and gravel, to make the concrete from which roads, bridges, buildings, and other structures are made. Aggregate.—The crushed stone used in making concrete is known as concrete aggregate. This is a major use for Illinois limestones and dolomites. Large amounts of stone aggregate also are used in bituminous roads, popularly called “blacktop” roads. Agricultural Uses.—Agricultural limestone (agstone) is applied to farm land to neutralize soil acids and otherwise benefit the soil. Both limestone and dolomite are so used. Chickens are fed small limestone chips to provide calcium for the formation of egg shells. Pigs and cows get calcium from mineral supplements containing powdered pure limestone. Figure 4—An underground limestone mine. Other Uses.—Illinois limestone or dolomite is used in steel making, as building stone and marble, as road stone, as ballast for the road beds of railroad tracks, for making refractory dolomite used in the steel industry, and for a variety of less common uses. Quarries There are about 200 stone quarries in Illinois. Most of the larger quarries (fig. 3) are in the Chicago, Joliet, Kankakee, and East St. Louis areas, but one or more limestone or dolomite quarry occurs in many counties. If all the stone taken from Illinois quarries in 1963 were removed from a hole 100 feet square, the hole would penetrate into the earth about 8 miles. It would take more than 350,000 railroad cars holding 100 tons each to haul away the stone. Limestone, dolomite, and their products added over 80 million dollars to the economy of the state in 1963, approximately 8 dollars for each person in Illinois. Most Illinois limestone and dolomite is quarried from open pits, but in some places, as in the rocky bluffs along the Mississippi River, the stone is taken from underground mines (fig. 4). There is also a dolomite mine in Chicago. At the quarries the first step is the removal of the earth overlying the stone. Next, in both pit and mine, the stone is blasted to free it from the parent deposit and break it into pieces. Mechanical shovels (fig. 3) load the stone into trucks that take it to the crushing plant where powerful crushers further break the stone into pieces. The pieces are sorted into various sizes by large screens. At some of the plants, the stone is ground into powder. Location of Limestone Deposits 10 11 The geologic map of Illinois prepared by the Illinois State Geological survey shows, with reasonable exactness, what bedrock formations would crop out at the surface if the overlying clay, sand, gravel, and earth were removed. Thick dolomite formations would be exposed in much of the northern fifth of the state, but would be rare elsewhere. Thick limestone formations would occur in an almost continuous zone, varying in width from 3 to 25 miles, along the Mississippi River from Rock Island to southern Illinois and then eastward across the extreme southern tip of the state. Limestone also would be seen along the Illinois River from Havana southward. In the central area of the state, limestones are present, but they are rarely over 25 and often less than 15 feet thick. Consequently, most of the larger quarries are in the northern, western, and southern parts of Illinois. The thinner limestones, nonetheless, are of much importance and are quarried at many places, chiefly to provide agricultural limestone, road stone, and limestone for making cement. The Geological Survey locates and maps limestone and dolomite deposits and analyzes and tests samples to determine the best possible uses for the stone. Many reports have been published about the character and general use of the deposits in various parts of the state. Other reports deal with the use of limestone and dolomite for specific purposes such as cement making, building and decorative stone, rock wool, terrazzo chips, and lime. METALLIC ORES AND FLUORSPAR Lead and Zinc Lead mining was one of the earliest industries of Illinois. The early settlers’ need for bullets for procuring food and for defense of their lives and property made lead an important commodity, and the deposits of lead ore in the northwestern corner of Illinois were quickly exploited. The ore was the mineral galena (fig. 5), for which the city of Galena in Jo Daviess County is believed to have been named. Figure 5—Galena with cubic cleavage blocks in foreground. Galena is a dark, shiny mineral that breaks readily into cubes or combinations of cubes. It is composed of lead and sulfur (PbS). Galena itself is not suitable for use as a metal; the lead must first be separated from the sulfur. The earliest method of recovering lead from galena was crude. A pile of logs, smaller pieces of wood, and ore was built on sloping ground. Just below it a pit was dug. When the wood was set on fire, the heat caused the lead and sulfur to separate, and the molten lead trickled down into the pit. The smelting process was later improved, and stone “furnaces” were built to house the operations. Crevice Deposits and Residual Deposits.—Most of the lead ore mined in the early days of the northwestern Illinois mining district came from crevice deposits in the dolomite bedrock and from residual deposits at or near the surface of the ground. The crevices were vertical narrow joints or fissures. Ore was not continuously present along them but occurred from place to place in “pods” (fig. 6 and fig. 7). Dimensions of the pods varied, but typical ones were about 3 feet wide, 5 feet high, and a few to a few hundred feet long. The galena, for the most part, occurred in a mixture of clay and weathered dolomite that filled, or partly filled, the crevices. The residual deposits were found where the action of the weather for many thousands of years had dissolved the dolomite from the outcropping parts of a crevice deposit and left behind a residue of brown or red clay containing galena. Some of the crevice and residual deposits worked by the early miners cropped out at the surface, but most of them were covered by earth. Other crevices were exposed in the bluffs of the Mississippi River and extended back into them for 1,000 feet or more. Figure 6—Diagrammatic cross section of two crevice deposits. A reaches ground surface and is filled with clay; B is only partly clay filled. Galena coats parts of the walls and occurs as pieces scattered through the clay. Typical crevices are about 3 feet wide and 5 feet high. SOIL A GALENA CLAY AND ROTTED DOLOMITE B GALENA CLAY AND ROTTED DOLOMITE DOLOMITE When the richer deposits of ore in the crevices were worked out, some mines were deepened into the dolomite bedrock, but usually less rather than more galena was found. As the amount of galena decreased, however, another mineral, which had been present before in only small amounts, was found in increasing quantities. This was sphalerite—a yellow, brown, or black mineral of resinous appearance that is composed of zinc and sulfur (ZnS). It does not look like a metallic ore. 12 13 14 At first the sphalerite was not used because there were no smelters in the area that could separate the zinc from the sulfur with which it was combined in the ore. Between 1850 and 1870, however, smelters were built in northwestern Illinois and southern Wisconsin and the ore was shipped there. Sphalerite is now the principal ore mineral produced in northwestern Illinois. The sphalerite and galena of southern Illinois, described later, are similar to that found in northwestern Illinois. Figure 7—Crevice lead mine. Miner pries ore loose and pushes it into car at bottom of crevice. Shiny galena layer occurs above his head and another at level of his waist. Mining and Milling.—One large mine is producing zinc and lead near Galena at present. Smaller mines operate irregularly. The ore may occur as pockets, irregularly shaped rather flat masses, vertical or inclined veins (fig. 8), or small particles scattered through the dolomite. The principal ore bodies that have been worked in recent years have been of irregular shape, both horizontally and vertically, and usually have been between 50 and 200 feet wide and from a few to as much as 100 feet high. They lie at a depth of roughly 300 feet. Blasting is required to loosen and break the ore. At the large mine the ore is brought to the surface by a hoist. In some relatively shallow mines an inclined tunnel has been driven to the ore body and the ore brought to the surface in trucks. Figure 8—Diagrammatic cross section of a zinc ore deposit showing flats and pitches. The deposit occurs in limestone and dolomite. Much of the ore is a mixture of dolomite, limestone, calcite, and sphalerite. Typical dimensions of such a deposit are about 30 feet high and 100 to 200 feet wide. ORE PITCHES FLATS Because the ore consists of galena and sphalerite attached to and scattered through dolomite, it must be milled to free and separate the metals from the rock. Crushing, grinding, and other operations are involved. The dolomite is discarded and the galena and sphalerite concentrates are shipped away to be smelted. No smelters have operated in the Galena area for some time. Aids to Prospecting.—Finding deposits of ore 300 feet underground is not easy. Inspection of the surface usually tells little. To find and outline a commercial ore deposit many holes often must be drilled to explore the unexposed rock strata. Because this is a costly process, every possible means is employed to drill the holes where ore is most likely to be found. This is where geologists are useful—geologists of the mining companies and of the Illinois Geological Survey. Three examples of how their investigations help to find ore are given here. It was noted early in the development of the northwestern Illinois mining district that zinc ore deposits were most common along small downfolds in the bedrock, called synclines, that were a few hundred feet wide and a mile or so long. The synclines were associated with much larger synclines that extended for several miles. A map prepared by the Illinois Geological Survey shows the possible location and extent of many of these downfolds and has had much practical use in the selection of the most promising areas for test drilling to find ore. The Survey also collects the records of borings made by companies and individuals in their search for ore. The records are on permanent file at the Survey offices and are valuable in several ways. Some indicate where no ore was found and where it is, therefore, useless to drill further; others show only traces of ore but suggest that more drilling in the vicinity might discover a deposit large enough to be mined profitably. Still other records are of borings that encountered rich ore in which mines have been developed. The third aid to prospecting is the study of ore bodies and their minerals to determine how the deposits were formed. The ore bodies have been and are being studied in the mines. Ore specimens are carefully examined in the Survey laboratories. If geologists can learn how the known deposits were formed, it may be possible to direct exploration into promising new areas. Fluorspar In the southeastern tip of Illinois lie deposits of a mineral that contains the chemical element fluorine. This element is used in making the propellant that activates aerosol sprays, a plastic that resists chemicals and oil and is strong enough to be used for bearings, compounds that are said to help to prevent tooth decay, and many other useful chemicals. The mineral is fluorite (fig. 9), commonly called fluorspar. It is composed of calcium fluoride (CaF₂), a compound of calcium and fluorine, and is a glassy mineral that is generally white or gray but may be purple, rose, yellow, blue, or green. In rare instances it is colorless. Fluorspar mining in Hardin and Pope Counties began with lead mining. Galena was first discovered there in 1839 in a well being dug at the town of Rosiclare. Mining of galena began in the early 1840’s, and somewhat later ore was being smelted by three furnaces, all of which have long since disappeared. 15 16 18 17 The veins that were worked for galena also contained fluorspar, but as there was little or no use for fluorspar in the 1840’s it was considered waste. In time, uses developed, however, and about 1870 it was mined and shipped in commercial quantities. Since then the tonnage and value of the fluorspar produced from the Rosiclare area have increased until fluorspar is the major product. Figure 9—Group of cubic fluorite crystals. The fluorspar mining district north of the town of Cave in Rock in eastern Hardin County also was an early producer of galena. In that area the fluorspar-galena deposits are elongate and approximately flat. The first miners followed the ore bodies from outcrops by tunneling into the hillsides. In the late 1930’s and early 1940’s, many holes were drilled into the bedrock in search of new deposits. Ore was found that contained not only galena and fluorspar but also important amounts of sphalerite. Vein Deposits.—In the Rosiclare district, the fluorspar and its accompanying minerals occur as steeply inclined veins a few inches to 25 feet or more wide (fig. 10), usually in limestone strata. The veins are not uniformly thick but widen or narrow from place to place both vertically and horizontally. They occur along faults—planes along which the rocks of the earth’s crust have broken and slipped. A fault may be a single plane of slippage but more often is a zone of broken and displaced rocks. In most of the faults that contain fluorspar, the slippage is vertical, or nearly so. Along one of the faults in the Rosiclare district, the rocks on one side of the fault have moved downward as much as 650 feet in relation to the rocks on the other side. Some faults are more than 10 miles long, and the depth to which they extend into the earth is unknown. Fluorspar has been mined from one of them at depths of 800 feet. Not all faults, nor all parts of any one fault, contain fluorspar. Figure 10—Diagrammatic cross section of fluorspar vein along a fault. The strata on the left side of the fault have moved downward with reference to those on the right side. SOIL FAULT FLUORSPAR VEIN ALONG FAULT down SANDSTONE A LIMESTONE B SHALE C SANDSTONE D LIMESTONE E up LIMESTONE B SHALE C SANDSTONE D LIMESTONE E Bedding Deposits.—In contrast to the vein deposits of the Rosiclare district, the bedding deposits of the Cave in Rock area are flat, or nearly flat, commonly 5 to 15 feet thick, and from a few to 200 feet wide (fig. 11). They may be as much as 2000 feet long, widening or narrowing and thickening or thinning throughout their extent. They are called bedding deposits because they lie along the beds or layers of the limestone in which they occur. Most of the ore bodies are associated with a fracture or a small fault. Figure 11—Diagrammatic cross section of bedding deposit of fluorspar, lead, and zinc ore. SOIL SANDSTONE AND SHALE ORE LIMESTONE FRACTURE OR SMALL FAULT Grades and Uses of Fluorspar.—There are three principal grades of fluorspar—metallurgical, acid, and ceramic. The metallurgical spar is used as a flux in making steel and in metal foundries. Acid spar is used to make hydrofluoric acid, which plays a part in the preparation of uranium isotopes and in the production of a synthetic mineral essential in refining aluminum. The acid is also used in the production of high-octane gasoline and is the basis for a variety of important chemical compounds, among them refrigerants and insecticides. Ceramic grade fluorspar is used in making enamels, glazes, and certain kinds of glass. Mining and Milling.—Fluorspar and its associated ores are mined in different ways in the Rosiclare and Cave in Rock districts because the types of deposits differ. However, in both areas most of the larger mines are entered by vertical shafts. In the mines, explosives are placed in holes drilled by machines and are then detonated to shoot down the ore (fig. 12). Mine cars, trucks, or conveyor belts carry the ore to the bottom of the mine shaft where hoists raise it to the mills at the surface. In the mills a variety of ore-classifying machines separate the galena, sphalerite, and fluorspar from the waste mineral materials (chiefly limestone and calcite) with which they occur. Some fluorspar after the separation process is almost flour-fine. To increase its use, much of this spar is mixed with a binder and made into 19 20 pellets or briquets one-half to one inch in size. Figure 12—Machine loading fluorspar ore in mine near Cave in Rock. Geological and Chemical Studies.—Because much of the fluorspar produced in southern Illinois has come from veins along faults, geologists have mapped the faults of the area by investigating the distribution and nature of the various bedrock outcrops. The work was complicated by the mantle of earth and vegetation that covers the bedrock at many places. However, a geologic map was made that shows where the various rock formations—sandstone, limestone, and shale—lie beneath the surface and where the numerous faults crisscross the district. The first geologic map of the fluorspar district was made in 1920 by the Illinois and U. S. Geological Surveys. New maps on a much larger scale have been made recently by the Illinois Survey to meet the needs of the modern fluorspar industry. The Illinois Survey also has studied the ores and ore deposits of southern Illinois to determine how they were formed. The records of many borings and pits sunk to find ore have been collected and filed at the Survey to guide future prospecting. Survey chemists are finding new uses for Illinois fluorspar. Their research has produced new organic fluorine compounds that are being tested for use in agriculture, medicine, and industry. They also have worked out easier and cheaper methods of making certain fluorine compounds. Survey chemical engineers have helped to obtain needed information about the physical properties of the pellets made from fluorspar powder. Origin of Illinois Ore Deposits The ore deposits of northwestern and southern Illinois were formed so many millions of years ago that it is possible to propose only theories of their origin. Most geologists think that the minerals, dissolved in warm or hot water, came from deep in the earth. Perhaps the mineral-bearing water came from, or was associated with, rocks that were or had been molten (igneous rocks), but it may have had some other source. Why the ores occur where we now find them is not fully known. The cooling of the solutions and the lessening of pressure as the solutions rose toward the surface may have had a part in ore deposition. Faults and the nature of the rocks encountered by the depositing solutions also appear to have had an influence. Illinois as a Mining State Although Illinois is not usually thought of as a mining state, northwestern and southern Illinois together produced in 1963 nearly $5,000,000 worth of zinc, about $600,000 worth of lead, and $6,500,000 worth of fluorspar. The annual total value is about $12,000,000. The southern Illinois fluorspar district has another distinction—for many years its mines have been the major domestic source of the nation’s fluorspar. SILICA SAND About 450,000,000 years ago, a shallow ocean covered Illinois. Its waves and currents carried clean white sand and deposited it as curving beaches, sand bars, and dunes. This sand differed from many sands in that it was composed almost exclusively of grains of the mineral quartz instead of being a mixture of quartz and other minerals. Quartz is composed of silica (SiO₂), and sands such as the ancient Illinois sand that are composed of quartz are known as silica sands. Quartz is very hard and will scratch glass and some steel. Perfect quartz crystals, which are rare, are longer than they are thick and end in pyramids. Probably not many grains of the ancient sand came from perfect crystals; they more likely resulted from the decaying and breaking down of rocks such as granite, which are mixtures of quartz grains and other mineral particles. The quartz grains probably did not come directly from their source to Illinois. Instead, it is likely they first were deposited elsewhere and formed into sandstone. That sandstone was subsequently broken down by weathering agents and the grains transported to the ancient Illinois sea by streams. As a result of the erosive action of the agents that transported them, many of the originally angular grains, particularly the coarser ones, were rounded and their surfaces dulled like that of frosted glass (fig. 13). Consequently, they appear white, although they actually are colorless. Since the ancient sea deposited its silica sand, other seas have covered Illinois at various times and each has left deposits of sand, mud, or limy materials. The silica sand thus was buried by hundreds of feet of other sediments and became sandstone. This sandstone is called the St. Peter Sandstone. It is named from the St. Peter River, now the Minnesota River, in Minnesota where the sandstone was first described and named by geologists. The overlying deposits also were consolidated into rock. 21 23 22 24 St. Peter Sandstone is exposed at the surface at many places in northern Illinois and in one small area in the western part of the state. The sandstone exposed in northern Illinois generally varies from 125 to 300 feet thick. The fact that it crops out at the surface indicates that the materials that formerly covered it have been removed. The uncovering was not a single, simple event but rather a series of events that took place at various times during the many years since the St. Peter sand was deposited. Among these was the up-bowing of the rocks of central northern Illinois into a broad arch. Streams then began to cut across the arched rock, slowly but persistently stripping away the top layers until the core of the arch was laid bare. Among the rocks thus exposed was the St. Peter Sandstone, which may be seen in northern Illinois in the valleys and tributaries of the Rock River near Dixon and Oregon and along the Illinois and Fox Rivers and some of their tributaries near Ottawa, Wedron, Millington, and Troy Grove. The St. Peter Sandstone at Starved Rock and Matthiessen state parks near LaSalle and along the highway between Dixon and Oregon is eroded into scenic bluffs and canyons. Figure 13—Enlarged photograph of St. Peter sand showing the rounded and frosted character of the grains. Silica Sand Industry The Illinois silica sand industry is based on the St. Peter Sandstone. It centers around Ottawa, Wedron, Troy Grove, and Utica in LaSalle County and in Oregon in Ogle County. Two principal grades of silica sand are produced—washed and crude. The value of the silica sand produced in Illinois in 1963 was about $9,000,000. Washed Sand.—Although the St. Peter Sandstone is composed almost entirely of quartz grains, a small amount of clay is present. For some uses it is not necessary to remove the clay, for others its elimination is important and is achieved by washing the sand. In the mining of silica sand that is to be washed, the sandstone is first blasted loose from the parent deposit to break it into sand or pieces of various sizes. Some of the larger pieces may require a second blasting to disintegrate them. At some pits the material is loaded mechanically and transported to the washing plant. At others a powerful stream of water is directed against the broken sandstone (fig. 14) and the resulting mixture of sand and water flows to a collecting basin from which it is pumped through large pipes to the processing mill. In both types of operation the sand is thoroughly washed at the plants. After it is washed, the sand is further processed to suit the needs of its users. Much of it is screened into different size grades. Uses of Washed Silica Sand.—The washed silica sand produced in Illinois has many uses, some of which are briefly mentioned below. The suitability of the sand for some purposes depends in part on its having been screened to specified sizes. The high purity of Illinois washed silica sand makes it suitable for making glass, which is more than half silica sand. Each year over a million tons is used for this purpose. The purity of the sand also is of importance for chemical and metallurgical uses such as the manufacture of sodium silicate and silicon carbide and in alloying. The hardness of the sand makes it useful for grinding large sheets of plate glass to prepare them for polishing and also makes it an effective abrasive agent for sandblasting. Metal castings in foundries and the exteriors of buildings are cleaned by this process. Illinois produces thousands of tons of sand yearly for such abrasive purposes. Because the coarser grains of the washed silica sand are rounded, strong, and available in uniform sizes, oil operators use thousands of tons of it annually in the hydraulic fracturing of oil-bearing strata. The sand is mixed with oil, other petroleum products, or water and is forced by powerful pumps into sandstone or limestone formations that contain oil. The great force thus exerted opens fractures in the rock strata and pushes the liquid and sand into them. When the pressure is relieved, the sand grains serve as props to hold the fractures open. The oil can then flow more easily into the wells and oil production is thus increased. The washed sand, because it is clean and does not dissolve in water, is used to filter impurities from drinking water. Its whiteness makes it a desirable constituent in plaster, mortar, and precast building panels. Figure 14—Hydraulic mining of silica sand near Ottawa. Because it is round grained and withstands high temperatures without melting, large tonnages of the washed silica sand are used to make molds into which molten metal is poured to make various kinds of castings. A special type of coarse silica sand from Illinois that is carefully prepared so that it is always of the same grain size is used throughout the world as a standard in laboratories that test cement and other commercial products. Figure 15—Loading crude silica sand. 25 27 26 Some silica sand is ground to a fine, white powder. The powder, called ground quartz, ground silica, silica flour, or potter’s flint, has many uses. It is an ingredient in paints, potters use it in making pottery and china, it goes into scouring powders, into molds used for precision types of metal castings, and into enamels. Crude Silica Sand.—The crude silica sand produced from the St. Peter Sandstone generally is yellow or yellowish white and is not washed before it is used. It probably originally was white, but iron oxide, similar to the rust that forms on iron, now coats many of the sand grains and colors the small amount of clay in the sand. Thousands of tons of crude silica sand are mined annually (fig. 15). Because it is highly heat resistant, foundries buy much of it to make the molds used for castings, especially steel castings, and for automobile engine blocks, train wheels, and a variety of other metal products. Crude silica sand also is used around industrial furnaces to seal cracks and openings to prevent the loss of heat, in certain ceramic products, and for adjusting the silica content of the raw materials used for making portland cement. Studies of the St. Peter Sandstone The Illinois Geological Survey has made field studies and prepared maps showing where the St. Peter Sandstone is exposed in northern and western Illinois. Many samples have been screened and examined under a microscope to determine how the sand of different deposits, or different parts of the same deposit, varies in grain size and mineral composition. The possibility of using Illinois silica sand for making silica brick also has been investigated. GRAVEL AND SAND Some 225,000 years ago, most of what is now Illinois was buried under the ice of the Illinoian glacier. Two earlier glaciers had covered large parts of Illinois, and another, known as the Wisconsinan glacier, came into the state later, about 50,000 to 70,000 years ago (fig. 16). The relatively small glaciers in the United States today, such as those in the northern Rocky Mountains, are concentrated in valleys and are called valley glaciers. The glaciers that covered Illinois were parts of huge ice sheets that extended over much of the North American continent and are called continental glaciers. They spread over most of Canada, then pushed southward to bury New England and a great area in the north-central part of the United States north of the Ohio and Missouri Rivers. Formation of Gravel and Sand Deposits As the glacial ice edged slowly southward from Canada, it froze fast to and picked up soil and loose pieces of rock, with enormous force tore away huge chunks of bedrock, and mixed and ground these materials together (fig. 17). Into Illinois the glacier carried rock materials from Canada, Wisconsin, Minnesota, and Michigan; other rock fragments were picked up in Illinois as the ice front advanced. When the glacier melted, it left behind its load of rock flour and rock fragments, much of it as a gray clay containing pebbles, cobbles, and boulders. Geologists call such deposits glacial till. Figure 16—Extent of the exposed deposits of the Wisconsinan, Illinoian, and Kansan glaciers in Illinois, and the unglaciated areas of the state. UNGLACIATED WISCONSINAN GLACIER Freeport Fulton Peoria Decatur Charleston ILLINOIAN GLACIER Kewanee Waterloo Carbondale Harrisburg KANSAN GLACIER UNGLACIATED Hardin The ice in the continental glaciers usually crept forward, sometimes slowly, sometimes more rapidly. Whether the front of a glacier moved forward or back depended on the balance between the rate of forward motion of the ice and the rate of melting. When the ice advanced faster than it melted, the front of the glacier moved forward. When the glacial ice melted faster than it moved forward, the front of the glacier receded. When the rates of melting and advance were about equal, the front of the glacier stood still or moved back and forth in a narrow zone. 28 29 Figure 17—Striated boulder. Scratches and flattened surfaces were caused by abrasion by other rocks while boulder was embedded in glacial ice. When such a more or less stationary front existed, an enormous amount of clay, silt, sand, pebbles, and boulders was deposited in a belt only a few miles wide along the front of the glacier, creating a line of hills and ridges that extended for many miles. Such belts, called end moraines, can be seen today in many parts of Illinois. The building of end moraines often was accompanied by the release of great quantities of water (meltwater) from the melting ice. The water, laden with rock debris, flowed from the front of the glacier in many streams. As the meltwater flowed away from the glacier it sorted its load, although the sorting was rarely perfect. The heavy boulders and pebbles usually were dropped first, then the sand, next the silt, and finally the clay. In general, the farther the deposits were from the glacier the finer they were. The major streams frequently carried pebbles 50 to 100 miles from the glacier and it was many more miles before all the sand was dropped. They carried some of the fine silt and clay as far as the Gulf of Mexico. Sometimes the floods of glacial water were greater and flowed faster than usual and so were able to carry coarse rock materials farther. As a result, gravel was laid down on top of earlier sand deposits. Later there may have been further sand deposition. The debris-laden meltwater that flowed into valleys often deposited in them a considerable filling of sand and gravel. Some valleys were filled to a depth of as much as 100 feet. Such deposits are called valley fills or valley trains. Modern streams have cut their courses into many of these fills and even worn away large parts of them. Remnants of valley train deposits are now large terraces or benches along streams, many of them well above the present stream channels. Where many small streams flowed from the glacier, they deposited sand and gravel as a large apron in front of the glacier. Such deposits are called outwash plains and many of them extend for miles. Two other types of sand and gravel deposits made by glacial meltwaters also are significant. One was formed where water issued from the front of a glacier or poured into holes or crevasses in the ice. The sand and gravel in the water formed a deposit that now appears as a rounded hill associated with a terminal moraine and is called a kame. The second type of deposit was laid down in beds of streams flowing under, through, or on the glaciers and was left as a more or less continuous ridge of sand and gravel when the ice melted. Such a deposit is called an esker. Some eskers in Illinois are about a quarter of a mile wide and several miles long. Typical are the Kaneville Esker northwest of Aurora, the Adeline Esker south of Freeport, and the Exeter Esker west of Jacksonville. The deposits of both the Illinoian and Wisconsinan glaciers are widely distributed throughout the state. Melting of the Illinoian glacier caused comparatively little flooding; consequently, extensive gravel deposits were formed in only a few places. The ice of the Wisconsinan glacier, however, melted rapidly and produced great floods laden with sand and gravel. Thus, most major gravel deposits in Illinois are related to the Wisconsinan glacier. Wind sweeping across the sand and gravel deposits blew the sand into hills or sand dunes near such places as Havana, Prophetstown, Kankakee, and Watseka. Even today the wind shifts sand of long-forgotten glacial floods. Studies of Glacial Deposits The foregoing discussion of glaciers and their deposits is greatly simplified. For some time geologists of the Illinois Geological Survey have been mapping the moraines, valley trains, outwash plains, and other glacial deposits of the state. Because the Illinoian and Wisconsinan glaciers advanced and retreated several times, they built many moraines. The Survey has made a map (fig. 18) that shows the complexity of the moraines left by the Wisconsinan glacier. They are roughly concentric, indicating that the general shape of the glacier front remained about the same. Principal Commercial Sources of Sand and Gravel The sand and gravel industry is widely distributed throughout Illinois. The principal commercial sources of sand and gravel are valley trains and outwash plains. The Fox, Rock, Illinois, Mississippi, and Wabash Rivers and many smaller streams have terraces in their valleys that are parts of valley trains. In these deposits are some of the largest sand- and gravel-producing operations in the state. Composition An examination of glacial gravel deposits in Illinois reveals pebbles and larger pieces of many kinds of rock. Some are gray, others white, pink, brown, or black. They commonly include limestone, dolomite, granite, and many rocks with less common names such as quartzite, schist, and basalt. The limestone and dolomite were picked up by the glaciers from outcrops in northern Illinois, Wisconsin, and Michigan. Some of the granite pebbles resemble outcrops in Wisconsin; others look like granite that crops out in Canada. The quartzite probably came from Wisconsin, and black shale fragments found in some gravel deposits came from the floor of Lake Michigan or from western Michigan. Occasionally pieces of metallic copper are found that probably had their source in the Lake Superior copper-bearing area. 30 31 32 In addition to the sand associated with gravel deposits, extensive deposits of sand alone are found at many places in Illinois. Most of the sand grains are pieces of minerals that were constituents of rocks until weathering, the grinding action of the glaciers, and other erosive agencies broke the rocks into sand. The principal mineral in glacial sand is quartz, but many others occur in lesser amounts, including calcite, dolomite, feldspar, pyroxene, tourmaline, garnet, magnetite, and hornblende. Most of these are foreign to Illinois, although the calcite and dolomite may be native. Figure 18—Moraines left by Wisconsinan glacier. Modified from George E. Ekblaw, 1960 ILLINOIS STATE GEOLOGICAL SURVEY Figure 19—Gravel dredge, with plant for processing the gravel in background. Uses of Sand and Gravel In 1963 more than 27 million tons of sand and gravel, directly or indirectly of glacial origin, was sold by Illinois producers for almost 25 million dollars. The sand alone would have filled a child’s sand box, with an area of 8 square miles, to a depth of 1 foot. The gravel would have covered an even larger area. The gravel was used in making concrete for roads and buildings, for surfacing roads, for ballast for railroad tracks, and for other purposes. The sand found its way into plaster, mortar, concrete, and a variety of other products and uses. Some of it was produced for use as molding sand. Production of Sand and Gravel The production of sand and gravel from its deposits may be a relatively simple operation or one of considerable complexity. Gravel for surfacing a road may be dug from a conveniently located pit and loaded mechanically into trucks that haul it to the road. A large sand- and gravel-producing operation, however, may include not only mechanical equipment to load and transport the material but also a processing plant where it can be washed if necessary and screened to various sizes. In a “dry pit” operation, mechanical cranes or shovels pick up the gravel and sand and load it into trucks, railroad cars, or conveyor belts to be transferred to the processing plant. There clay and dirt may be washed out and the sand and gravel is sized by screens. Conveyor belts carry sand and gravel to the various processing operations and to storage bins or piles on the ground. A “wet pit” operation produces sand and gravel from an artificial pond or lake. In some operations the sand and gravel is mined by a dredge that floats on the water (fig. 19). In some pits, a stream of water is directed from the dredge against the bank of gravel to wash the gravel into the lake. A large metal pipe at the front of the dredge slants down into the water and sucks up the sand and gravel from the underwater part of the deposit. The gravel, sand, and water is then pumped through a pipe at the rear of the dredge to the processing plant on the shore. In some types of wet pit operations a large scoop or bucket operated from a crane on the shore, or by cables fastened to the shore, is used to dig sand and gravel from beneath the water. Dredges are used to pump up sand and gravel from the beds of Illinois rivers, especially the Mississippi, Ohio, and Wabash. The sand and gravel resources of many parts of the state have been mapped and studied by the Illinois Geological Survey, and work of this kind is continuing. SILICA (TRIPOLI) AND OTHER MINERAL MATERIALS OF EXTREME SOUTHERN ILLINOIS The hills of extreme southern Illinois contain several mineral materials that are entirely or largely restricted, in important quantities, to that part of the state. Some of them, such as silica and novaculite, come directly from bedrock deposits of great age; others, such as some of the sands and gravels, are of more recent origin. Silica (Tripoli) A mineral material unique in Illinois is the amorphous silica, or tripoli, mined in the hills of southern Illinois about 20 miles north of Cairo. Most of the silica mines are found at the heads of valleys or in tree-covered hill slopes along the less traveled roads. An arched opening 33 35 36 34 (fig. 20) with a road leading into it may be all that is visible of the mine from the outside. Inside are many rooms, some 30 feet high, separated by rounded pillars about 20 feet thick that have been left to support the arched mine roof. Most of the silica in the mines is white, and this is the part that is mined. A silica deposit is made up of layers—some of white, powdery rock material, others that look chalky but are firm or hard. Figure 20—Entrance to a silica mine. In the mines the silica is blasted loose from the natural deposit and loaded into trucks that take it to the processing mills at Elco and Tamms, where it is crushed and then transferred to huge grinding mills that pulverize it to a very fine powder. Air currents of different velocities separate the powder into various grades of fineness, and the finished silica goes into large paper bags for shipment. Origin of Silica.—Some of the history of the formation of silica deposits is not fully known, but it seems probable that their original character was quite different from what it is today. Investigations by Survey geologists suggest that the parent rock formation was limestone and chert. The limestone was composed of the mineral calcite, but scattered through it were myriads of small particles of quartz. Interlayered with it were bands and beds of chert that contained varying amounts of calcite. As the rocks above them were worn away by the ceaseless erosion of streams and rivers, these original deposits were uncovered. Rain and snow-water then worked down into the limestone and chert deposits through cracks and crevic...