Title: Industrial Minerals and Metals of Illinois
Author: J. E. Lamar
Release date: May 23, 2021 [eBook #65426]
Most recently updated: October 18, 2024
Language: English
Credits: Stephen Hutcheson and the Online Distributed Proofreading Team at https://www.pgdp.net
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
J. E. Lamar
The mineral resources of Illinois include many rocks andminerals of varied character and uses. From them aremade an array of everyday products whose sources maynot even be recognized by the consumer. The user of aglass bottle, for instance, rarely knows that it may have beenmade from Illinois silica sand, nor is the driver of an automobilegenerally aware that the Illinois concrete highway on which he isdriving probably was constructed from a mixture of cement, sandand gravel, or crushed stone that may have come from Illinoispits or quarries.
The significance of these rocks and minerals to the economyof Illinois is great, although often unappreciated. Of the morethan 600 million dollar value of all Illinois mineral production in1963, almost 200 million was from industrial minerals. The diversityand widespread distribution of these mineral resources lendvariety and balance to the mineral industry of the state, and theirproduction, processing, and utilization afford direct and indirectemployment to many people.
The term industrial minerals is used as a convenientgroup term for nonmetallic minerals that are not fuels. In Illinoisthey include limestone, dolomite, clay, shale, silica sand andother sands, fluorspar, tripoli (amorphous silica), ganister, novaculite,sandstone, feldspar-bearing sands, barite, gypsum, anhydrite,brines, greensand, oil shale, marl, peat, humus, andtufa. The metallic minerals of Illinois are galena (lead ore),sphalerite (zinc ore), pyrite, and marcasite.
This booklet briefly and nontechnically discusses theforegoing materials and some of the work the Illinois State Geological Surveydoes in gathering information about their occurrence,and character and in developing new uses.
The assistance of many Survey staff members and of manypeople in the Illinois mineral industry in the preparation of thisbooklet is acknowledged.
Limestone is a most versatile rock. Without it there wouldbe no portland cement for making concrete roads and buildings, nolime for plastering and chemical use, no agricultural limestone forfarms, and no crushed limestone for driveways. A widevariety of industries, from steel making to glass manufacturing,use limestone in one way or another.
The early settlers of Illinois recognized the value of limestoneand quarried stone blocks and slabs for making foundations,chimneys, and even houses. For mortar they used a mixture of sandand lime to hold the blocks together. The lime was made by heatinglimestone red hot in simple furnaces or kilns, the ruins of a few ofwhich may still be seen.
Illinois has two principal varieties of limestone, referredto technically as limestone and dolomite. “Limestone” may beused as a general name for both varieties.
Limestone consists principally of crystalline particles ofthe mineral calcite (fig. 1). This mineral is glassy in appearanceand is composed of calcium, carbon, and oxygen combined to formcalcium carbonate—CaCO₃. Dolomite is largely made of crystallineparticles of the mineral dolomite, which also has a glassyappearance and consists of calcium, magnesium, carbon, and oxygen—CaMg(CO₃)₂.The crystalline particles of limestone and dolomitevary in size. Some are coarse enough to be seen easily, othersare so small that they can be distinguished only with a microscope.
Almost all Illinois limestones were formed in seas thatcovered Illinois millions of years ago. The many different limestoneformations in Illinois suggest that oceans covered all orpart of the area several times. Numerous kinds of shell fish, corals,and other marine animals lived in these oceans and had shells andother hard parts made of calcium carbonate. Through countlessgenerations, these animal remains accumulated on the ocean floorand gradually were compacted and cemented into limestone (fig. 2).
Other Illinois limestones, however, were formed by thehardening of muds composed mainly of calcium carbonate thataccumulated on the floors of the ancient seas. Still other limestoneswere formed of a combination of animal remains and limemud.
Figure 1—Calcite crystals. Limestone is made up mainly of calcitecrystals, but they are less perfectly formed and are crowded together.
The coral reefs of the South Pacific Ocean have theircounterparts in Illinois. The ancient Illinois oceans containedextensive reefs that were built up just as the modern reefs have been.In northern Illinois, around Chicago for instance, a number of theancient reefs are now the site of stone quarries. In southwesternIllinois such reefs are a source of petroleum.
The dolomites of Illinois probably were originally limestones,but, either while the limestones were still beneath thesea or after the sea had withdrawn, magnesium was exchangedfor some of the calcium in the limestones. If the exchange tookplace under the sea, the sea water was the source of the magnesium.If it happened when the limestones were a part of the land, themagnesium was brought in by water circulating through the rock.Many of the marine animal fossils became difficult to recognizeafter the change, and the texture and general appearance of therock also were altered. Some of it became noticeably porous.
Figure 2—Limestone containing fossils.An Archimedes screw appearsat lower left, lace-like bryozoa inthe center, and fluted brachiopodshells at top and center.
Some of the major uses for Illinois limestone and dolomiteare mentioned below. Not every limestone or dolomite can be usedfor all purposes because for each use the stone must fulfill specialrequirements of a chemical or physical nature. For example,it must have high purity for lime, resistance to wear and weatherfor roads and buildings, and a pleasing appearance for decorativestone and marble.
Lime.—When limestone or dolomite is heated to a hightemperature, it undergoes a change and carbon dioxide is liberated.The weight of the gas set free is equal to somewhat less than halfthe weight of the rock if the rock is pure. The solid product remainingafter the gas has been driven off is known as lime. Theheating process is called burning.
Besides being used in making mortar and plaster, lime isvaluable in many other ways, especially in various chemicalprocesses of modern industry. Plants at Chicago and Quincymake 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 Illinoisfrom limestone and a smaller, carefully measured amount of clayor shale. Cement also is made at Joppa in southern Illinois. Theblend of materials is thoroughly ground and mixed, then heatedat a high temperature in huge rotating horizontal furnaces, calledkilns, until it forms a clinker. After it cools, the clinker is groundto a flourlike powder. This is basically the cement that binds togetherthe mixture of sand and limestone (or dolomite), or of sandand gravel, to make the concrete from which roads, bridges, buildings,and other structures are made.
Aggregate.—The crushed stone used in making concreteis known as concrete aggregate. This is a major use for Illinoislimestones and dolomites. Large amounts of stone aggregate alsoare used in bituminous roads, popularly called “blacktop” roads.
Agricultural Uses.—Agricultural limestone (agstone) is appliedto farm land to neutralize soil acids and otherwise benefitthe soil. Both limestone and dolomite are so used. Chickens arefed small limestone chips to provide calcium for the formation ofegg shells. Pigs and cows get calcium from mineral supplementscontaining powdered pure limestone.
Figure 4—An underground limestone mine.
Other Uses.—Illinois limestone or dolomite is used in steelmaking, as building stone and marble, as road stone, as ballastfor the road beds of railroad tracks, for making refractory dolomiteused in the steel industry, and for a variety of less common uses.
There are about 200 stone quarries in Illinois. Most ofthe larger quarries (fig. 3) are in the Chicago, Joliet, Kankakee,and East St. Louis areas, but one or more limestone or dolomitequarry occurs in many counties.
If all the stone taken from Illinois quarries in 1963 wereremoved from a hole 100 feet square, the hole would penetrate intothe earth about 8 miles. It would take more than 350,000 railroadcars holding 100 tons each to haul away the stone. Limestone,dolomite, and their products added over 80 million dollars to theeconomy of the state in 1963, approximately 8 dollars for each personin Illinois.
Most Illinois limestone and dolomite is quarried from openpits, but in some places, as in the rocky bluffs along the MississippiRiver, the stone is taken from underground mines (fig. 4).9There is also a dolomite mine in Chicago. At the quarries the firststep is the removal of the earth overlying the stone. Next, in bothpit and mine, the stone is blasted to free it from the parent depositand break it into pieces. Mechanical shovels (fig. 3) load thestone into trucks that take it to the crushing plant where powerfulcrushers further break the stone into pieces. The pieces are sortedinto various sizes by large screens. At some of the plants, thestone is ground into powder.
The geologic map of Illinois prepared by the Illinois StateGeological survey shows, with reasonable exactness, what bedrockformations would crop out at the surface if the overlying clay,sand, gravel, and earth were removed. Thick dolomite formationswould be exposed in much of the northern fifth of the state, butwould be rare elsewhere. Thick limestone formations would occurin an almost continuous zone, varying in width from 3 to 25 miles,along the Mississippi River from Rock Island to southern Illinoisand then eastward across the extreme southern tip of the state.Limestone also would be seen along the Illinois River from Havanasouthward.
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 limestonefor making cement.
The Geological Survey locates and maps limestone anddolomite deposits and analyzes and tests samples to determinethe best possible uses for the stone. Many reports have been publishedabout the character and general use of the deposits in variousparts of the state. Other reports deal with the use of limestoneand dolomite for specific purposes such as cement making, buildingand decorative stone, rock wool, terrazzo chips, and lime.
Lead mining was one of the earliest industries of Illinois.The early settlers’ need for bullets for procuring food and for defenseof their lives and property made lead an important commodity, and10the deposits of lead ore in the northwestern corner of Illinois werequickly exploited. The ore was the mineral galena (fig. 5), forwhich the city of Galena in Jo Daviess County is believed to havebeen named.
Figure 5—Galena with cubic cleavage blocks in foreground.
Galena is a dark, shiny mineral that breaks readily intocubes or combinations of cubes. It is composed of lead and sulfur(PbS). Galena itself is not suitable for use as a metal; the leadmust first be separated from the sulfur.
The earliest method of recovering lead from galena wascrude. A pile of logs, smaller pieces of wood, and ore was builton sloping ground. Just below it a pit was dug. When the woodwas set on fire, the heat caused the lead and sulfur to separate,and the molten lead trickled down into the pit. The smelting processwas later improved, and stone “furnaces” were built to house theoperations.
Crevice Deposits and Residual Deposits.—Most of the leadore mined in the early days of the northwestern Illinois miningdistrict came from crevice deposits in the dolomite bedrock and11from residual deposits at or near the surface of the ground. Thecrevices were vertical narrow joints or fissures. Ore was notcontinuously present along them but occurred from place to placein “pods” (fig. 6 andfig. 7). Dimensions of the pods varied, buttypical ones were about 3 feet wide, 5 feet high, and a few to afew hundred feet long. The galena, for the most part, occurred ina mixture of clay and weathered dolomite that filled, or partlyfilled, the crevices.
The residual deposits were found where the action of theweather for many thousands of years had dissolved the dolomitefrom the outcropping parts of a crevice deposit and left behind aresidue of brown or red clay containing galena.
Some of the crevice and residual deposits worked by theearly miners cropped out at the surface, but most of them werecovered by earth. Other crevices were exposed in the bluffs ofthe Mississippi River and extended back into them for 1,000 feetor more.
Figure 6—Diagrammatic cross sectionof two crevice deposits. A reachesground surface and is filled with clay;B is only partly clay filled. Galenacoats parts of the walls and occursas pieces scattered through the clay.Typical crevices are about 3 feetwide and 5 feet high.
When the richer deposits of ore in the crevices wereworked 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, wasfound in increasing quantities. This was sphalerite—a yellow,brown, or black mineral of resinous appearance that is composedof zinc and sulfur (ZnS). It does not look like a metallic ore.
At first the sphalerite was not used because there were nosmelters in the area that could separate the zinc from the sulfur12with which it was combined in the ore. Between 1850 and 1870,however, smelters were built in northwestern Illinois and southernWisconsin and the ore was shipped there. Sphalerite is now theprincipal ore mineral produced in northwestern Illinois.
The sphalerite and galena of southern Illinois, describedlater, are similar to that found in northwestern Illinois.
Figure 7—Crevice lead mine. Miner pries ore loose and pushes itinto car at bottom of crevice. Shiny galena layer occurs abovehis head and another at level of his waist.
Mining and Milling.—One large mine is producing zincand 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 scatteredthrough the dolomite. The principal ore bodies that have been workedin recent years have been of irregular shape, both horizontallyand vertically, and usually have been between 50 and 200 feet wideand from a few to as much as 100 feet high. They lie at a depthof roughly 300 feet.
Blasting is required to loosen and break the ore. At thelarge mine the ore is brought to the surface by a hoist. In somerelatively shallow mines an inclined tunnel has been driven to theore body and the ore brought to the surface in trucks.
Figure 8—Diagrammatic cross sectionof a zinc ore deposit showing flatsand pitches. The deposit occurs inlimestone and dolomite. Much ofthe ore is a mixture of dolomite,limestone, calcite, and sphalerite.Typical dimensions of such a depositare about 30 feet high and 100 to 200feet wide.
Because the ore consists of galena and sphalerite attachedto and scattered through dolomite, it must be milled to free andseparate the metals from the rock. Crushing, grinding, and otheroperations are involved. The dolomite is discarded and the galenaand sphalerite concentrates are shipped away to be smelted. Nosmelters have operated in the Galena area for some time.
Aids to Prospecting.—Finding deposits of ore 300 feet undergroundis not easy. Inspection of the surface usually tells little.To find and outline a commercial ore deposit many holes often mustbe drilled to explore the unexposed rock strata. Because this is acostly process, every possible means is employed to drill the holeswhere ore is most likely to be found. This is where geologistsare useful—geologists of the mining companies and of the IllinoisGeological Survey. Three examples of how their investigationshelp to find ore are given here.
It was noted early in the development of the northwesternIllinois mining district that zinc ore deposits were most commonalong small downfolds in the bedrock, called synclines, that werea few hundred feet wide and a mile or so long. The synclines wereassociated with much larger synclines that extended for severalmiles. A map prepared by the Illinois Geological Survey showsthe possible location and extent of many of these downfolds andhas had much practical use in the selection of the most promisingareas for test drilling to find ore.
The Survey also collects the records of borings made bycompanies and individuals in their search for ore. The recordsare on permanent file at the Survey offices and are valuable inseveral ways. Some indicate where no ore was found and whereit is, therefore, useless to drill further; others show only tracesof ore but suggest that more drilling in the vicinity might discovera deposit large enough to be mined profitably. Still other recordsare of borings that encountered rich ore in which mines have beendeveloped.
The third aid to prospecting is the study of ore bodies andtheir minerals to determine how the deposits were formed. The orebodies have been and are being studied in the mines. Ore specimensare carefully examined in the Survey laboratories. If geologistscan learn how the known deposits were formed, it may bepossible to direct exploration into promising new areas.
In the southeastern tip of Illinois lie deposits of a mineralthat contains the chemical element fluorine. This element is usedin making the propellant that activates aerosol sprays, a plasticthat resists chemicals and oil and is strong enough to be used forbearings, 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 calciumand fluorine, and is a glassy mineral that is generally white orgray but may be purple, rose, yellow, blue, or green. In rareinstances it is colorless.
Fluorspar mining in Hardin and Pope Counties began withlead mining. Galena was first discovered there in 1839 in a wellbeing dug at the town of Rosiclare. Mining of galena began in theearly 1840’s, and somewhat later ore was being smelted by threefurnaces, all of which have long since disappeared.
The veins that were worked for galena also contained fluorspar,but as there was little or no use for fluorspar in the 1840’s15it was considered waste. In time, uses developed, however, andabout 1870 it was mined and shipped in commercial quantities.Since then the tonnage and value of the fluorspar produced from theRosiclare 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 inRock in eastern Hardin County also was an early producer of galena.In that area the fluorspar-galena deposits are elongate and approximatelyflat. The first miners followed the ore bodies from outcropsby tunneling into the hillsides. In the late 1930’s and early1940’s, many holes were drilled into the bedrock in search of newdeposits. Ore was found that contained not only galena and fluorsparbut also important amounts of sphalerite.
Vein Deposits.—In the Rosiclare district, the fluorsparand its accompanying minerals occur as steeply inclined veins afew inches to 25 feet or more wide (fig. 10), usually in limestonestrata. The veins are not uniformly thick but widen or narrowfrom place to place both vertically and horizontally. They occur16along faults—planes along which the rocks of the earth’s crusthave broken and slipped. A fault may be a single plane of slippagebut more often is a zone of broken and displaced rocks. Inmost 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 muchas 650 feet in relation to the rocks on the other side. Some faultsare more than 10 miles long, and the depth to which they extendinto the earth is unknown. Fluorspar has been mined from one ofthem at depths of 800 feet. Not all faults, nor all parts of anyone fault, contain fluorspar.
Figure 10—Diagrammatic cross sectionof fluorspar vein along a fault.The strata on the left side of thefault have moved downward withreference to those on the right side.
Bedding Deposits.—In contrast to the vein deposits of theRosiclare district, the bedding deposits of the Cave in Rock areaare flat, or nearly flat, commonly 5 to 15 feet thick, and from afew to 200 feet wide (fig. 11). They may be as much as 2000 feetlong, widening or narrowing and thickening or thinning throughouttheir extent. They are called bedding deposits because they liealong the beds or layers of the limestone in which they occur.Most of the ore bodies are associated with a fracture or a smallfault.
Figure 11—Diagrammatic cross sectionof bedding deposit of fluorspar,lead, and zinc ore.
Grades and Uses of Fluorspar.—There are three principalgrades of fluorspar—metallurgical, acid, and ceramic. The metallurgicalspar is used as a flux in making steel and in metal foundries.Acid spar is used to make hydrofluoric acid, which plays apart in the preparation of uranium isotopes and in the productionof a synthetic mineral essential in refining aluminum. The acidis also used in the production of high-octane gasoline and is thebasis for a variety of important chemical compounds, among themrefrigerants and insecticides. Ceramic grade fluorspar is used inmaking enamels, glazes, and certain kinds of glass.
Mining and Milling.—Fluorspar and its associated oresare mined in different ways in the Rosiclare and Cave in Rockdistricts because the types of deposits differ. However, in bothareas most of the larger mines are entered by vertical shafts.In the mines, explosives are placed in holes drilled by machinesand are then detonated to shoot down the ore (fig. 12). Mine cars,trucks, or conveyor belts carry the ore to the bottom of the mineshaft where hoists raise it to the mills at the surface. In the millsa variety of ore-classifying machines separate the galena,18sphalerite, and fluorspar from the waste mineral materials (chieflylimestone and calcite) with which they occur. Some fluorspar afterthe separation process is almost flour-fine. To increase its use,much of this spar is mixed with a binder and made into pellets orbriquets 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 thefluorspar produced in southern Illinois has come from veins alongfaults, geologists have mapped the faults of the area by investigatingthe distribution and nature of the various bedrock outcrops.The work was complicated by the mantle of earth and vegetationthat covers the bedrock at many places. However, a geologic mapwas made that shows where the various rock formations—sandstone,limestone, and shale—lie beneath the surface and where the numerousfaults crisscross the district.
The first geologic map of the fluorspar district was madein 1920 by the Illinois and U. S. Geological Surveys. New mapson a much larger scale have been made recently by the IllinoisSurvey to meet the needs of the modern fluorspar industry.
The Illinois Survey also has studied the ores and ore depositsof southern Illinois to determine how they were formed.19The records of many borings and pits sunk to find ore have beencollected 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 compoundsthat are being tested for use in agriculture, medicine, andindustry. They also have worked out easier and cheaper methodsof making certain fluorine compounds. Survey chemical engineershave helped to obtain needed information about the physical propertiesof the pellets made from fluorspar powder.
The ore deposits of northwestern and southern Illinoiswere formed so many millions of years ago that it is possible topropose only theories of their origin. Most geologists think thatthe minerals, dissolved in warm or hot water, came from deep inthe earth. Perhaps the mineral-bearing water came from, or wasassociated with, rocks that were or had been molten (igneousrocks), but it may have had some other source. Why the ores occurwhere we now find them is not fully known. The cooling ofthe solutions and the lessening of pressure as the solutions rosetoward the surface may have had a part in ore deposition. Faultsand the nature of the rocks encountered by the depositing solutionsalso appear to have had an influence.
Although Illinois is not usually thought of as a miningstate, northwestern and southern Illinois together produced in 1963nearly $5,000,000 worth of zinc, about $600,000 worth of lead,and $6,500,000 worth of fluorspar. The annual total value isabout $12,000,000.
The southern Illinois fluorspar district has another distinction—formany years its mines have been the major domesticsource of the nation’s fluorspar.
About 450,000,000 years ago, a shallow ocean coveredIllinois. Its waves and currents carried clean white sand and depositedit as curving beaches, sand bars, and dunes. This sanddiffered from many sands in that it was composed almost exclusivelyof grains of the mineral quartz instead of being a mixtureof quartz and other minerals.
Quartz is composed of silica (SiO₂), and sands such asthe ancient Illinois sand that are composed of quartz are known assilica sands. Quartz is very hard and will scratch glass and somesteel. Perfect quartz crystals, which are rare, are longer thanthey are thick and end in pyramids. Probably not many grains ofthe ancient sand came from perfect crystals; they more likely resultedfrom 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 fromtheir source to Illinois. Instead, it is likely they first were depositedelsewhere and formed into sandstone. That sandstone wassubsequently broken down by weathering agents and the grainstransported to the ancient Illinois sea by streams.
As a result of the erosive action of the agents that transportedthem, many of the originally angular grains, particularlythe coarser ones, were rounded and their surfaces dulled likethat of frosted glass (fig. 13). Consequently, they appear white,although they actually are colorless.
Since the ancient sea deposited its silica sand, otherseas have covered Illinois at various times and each has leftdeposits of sand, mud, or limy materials. The silica sand thuswas buried by hundreds of feet of other sediments and became sandstone.This sandstone is called the St. Peter Sandstone. It isnamed from the St. Peter River, now the Minnesota River, inMinnesota where the sandstone was first described and named bygeologists. The overlying deposits also were consolidated intorock.
St. Peter Sandstone is exposed at the surface at manyplaces in northern Illinois and in one small area in the westernpart of the state. The sandstone exposed in northern Illinoisgenerally varies from 125 to 300 feet thick. The fact that it cropsout at the surface indicates that the materials that formerly coveredit have been removed.
The uncovering was not a single, simple event but rathera series of events that took place at various times during the manyyears since the St. Peter sand was deposited. Among these wasthe up-bowing of the rocks of central northern Illinois into a broadarch. Streams then began to cut across the arched rock, slowlybut persistently stripping away the top layers until the core of thearch was laid bare. Among the rocks thus exposed was the St. PeterSandstone, which may be seen in northern Illinois in the valleysand tributaries of the Rock River near Dixon and Oregon and alongthe Illinois and Fox Rivers and some of their tributaries nearOttawa, Wedron, Millington, and Troy Grove. The St. Peter21Sandstone at Starved Rock and Matthiessen state parks near LaSalleand along the highway between Dixon and Oregon is eroded intoscenic bluffs and canyons.
Figure 13—Enlarged photograph of St.Peter sand showing the rounded andfrosted character of the grains.
The Illinois silica sand industry is based on the St. PeterSandstone. It centers around Ottawa, Wedron, Troy Grove, andUtica in LaSalle County and in Oregon in Ogle County. Two principalgrades of silica sand are produced—washed and crude. Thevalue of the silica sand produced in Illinois in 1963 was about$9,000,000.
Washed Sand.—Although the St. Peter Sandstone is composedalmost entirely of quartz grains, a small amount of clay ispresent. For some uses it is not necessary to remove the clay,22for others its elimination is important and is achieved by washingthe sand.
In the mining of silica sand that is to be washed, the sandstoneis first blasted loose from the parent deposit to break it intosand or pieces of various sizes. Some of the larger pieces mayrequire a second blasting to disintegrate them.
At some pits the material is loaded mechanically and transportedto the washing plant. At others a powerful stream of wateris directed against the broken sandstone (fig. 14) and the resultingmixture of sand and water flows to a collecting basin fromwhich it is pumped through large pipes to the processing mill.
In both types of operation the sand is thoroughly washed atthe plants. After it is washed, the sand is further processed tosuit the needs of its users. Much of it is screened into differentsize grades.
Uses of Washed Silica Sand.—The washed silica sand producedin Illinois has many uses, some of which are briefly mentionedbelow. The suitability of the sand for some purposes dependsin part on its having been screened to specified sizes.
The high purity of Illinois washed silica sand makes itsuitable for making glass, which is more than half silica sand.Each year over a million tons is used for this purpose. Thepurity of the sand also is of importance for chemical and metallurgicaluses such as the manufacture of sodium silicate and siliconcarbide and in alloying.
The hardness of the sand makes it useful for grinding largesheets of plate glass to prepare them for polishing and also makesit an effective abrasive agent for sandblasting. Metal castings infoundries and the exteriors of buildings are cleaned by this process.Illinois produces thousands of tons of sand yearly for such abrasivepurposes.
Because the coarser grains of the washed silica sand arerounded, strong, and available in uniform sizes, oil operators usethousands of tons of it annually in the hydraulic fracturing of oil-bearingstrata. The sand is mixed with oil, other petroleum products,or water and is forced by powerful pumps into sandstone orlimestone formations that contain oil. The great force thus exertedopens fractures in the rock strata and pushes the liquid and sandinto them. When the pressure is relieved, the sand grains serveas props to hold the fractures open. The oil can then flow moreeasily into the wells and oil production is thus increased.
The washed sand, because it is clean and does not dissolvein water, is used to filter impurities from drinking water.23Its 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 temperatureswithout melting, large tonnages of the washed silica sandare used to make molds into which molten metal is poured to makevarious kinds of castings.
A special type of coarse silica sand from Illinois that iscarefully prepared so that it is always of the same grain size isused throughout the world as a standard in laboratories that testcement and other commercial products.
Figure 15—Loading crude silica sand.
Some silica sand is ground to a fine, white powder. Thepowder, called ground quartz, ground silica, silica flour, or potter’sflint, has many uses. It is an ingredient in paints, potters25use it in making pottery and china, it goes into scouring powders,into molds used for precision types of metal castings, and intoenamels.
Crude Silica Sand.—The crude silica sand produced fromthe St. Peter Sandstone generally is yellow or yellowish whiteand is not washed before it is used. It probably originally waswhite, but iron oxide, similar to the rust that forms on iron, nowcoats many of the sand grains and colors the small amount ofclay in the sand. Thousands of tons of crude silica sand aremined 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 silicasand also is used around industrial furnaces to seal cracks andopenings to prevent the loss of heat, in certain ceramic products,and for adjusting the silica content of the raw materials used formaking portland cement.
The Illinois Geological Survey has made field studies andprepared maps showing where the St. Peter Sandstone is exposedin northern and western Illinois. Many samples have been screenedand examined under a microscope to determine how the sand ofdifferent deposits, or different parts of the same deposit, variesin grain size and mineral composition. The possibility of usingIllinois silica sand for making silica brick also has been investigated.
Some 225,000 years ago, most of what is now Illinois wasburied under the ice of the Illinoian glacier. Two earlier glaciershad covered large parts of Illinois, and another, known as theWisconsinan glacier, came into the state later, about 50,000 to70,000 years ago (fig. 16).
The relatively small glaciers in the United States today,such as those in the northern Rocky Mountains, are concentratedin valleys and are called valley glaciers. The glaciers that coveredIllinois were parts of huge ice sheets that extended over muchof the North American continent and are called continental glaciers.They spread over most of Canada, then pushed southward to buryNew England and a great area in the north-central part of theUnited States north of the Ohio and Missouri Rivers.
As the glacial ice edged slowly southward from Canada,it froze fast to and picked up soil and loose pieces of rock, withenormous force tore away huge chunks of bedrock, and mixed andground these materials together (fig. 17).
Into Illinois theglacier carried rock materialsfrom Canada, Wisconsin,Minnesota, andMichigan; other rockfragments were picked upin Illinois as the ice frontadvanced. When the glaciermelted, it left behindits load of rock flour androck fragments, much ofit as a gray clay containingpebbles, cobbles, andboulders. Geologists callsuch deposits glacial till.
Figure 16—Extent of the exposed depositsof the Wisconsinan, Illinoian,and Kansan glaciers in Illinois, andthe unglaciated areas of the state.
The ice in the continentalglaciers usuallycrept forward, sometimesslowly, sometimes morerapidly. Whether the frontof a glacier moved forwardor back depended on thebalance between the rateof forward motion of theice and the rate of melting.When the ice advancedfaster than itmelted, the front of theglacier moved forward.27When the glacial ice melted faster than it moved forward, the frontof the glacier receded. When the rates of melting and advancewere about equal, the front of the glacier stood still or moved backand forth in a narrow zone.
Figure 17—Striated boulder. Scratches and flattened surfaceswere caused by abrasion by other rocks while boulder was embeddedin glacial ice.
When such a more or less stationary front existed, anenormous amount of clay, silt, sand, pebbles, and boulders wasdeposited in a belt only a few miles wide along the front of theglacier, creating a line of hills and ridges that extended for manymiles. Such belts, called end moraines, can be seen today inmany parts of Illinois.
The building of end moraines often was accompanied bythe release of great quantities of water (meltwater) from the meltingice. The water, laden with rock debris, flowed from the front ofthe glacier in many streams.
As the meltwater flowed away from the glacier it sorted itsload, although the sorting was rarely perfect. The heavy bouldersand pebbles usually were dropped first, then the sand, next thesilt, and finally the clay. In general, the farther the deposits28were from the glacier the finer they were. The major streams frequentlycarried pebbles 50 to 100 miles from the glacier and it wasmany more miles before all the sand was dropped. They carriedsome of the fine silt and clay as far as the Gulf of Mexico.
Sometimes the floods of glacial water were greater andflowed faster than usual and so were able to carry coarse rockmaterials farther. As a result, gravel was laid down on top ofearlier sand deposits. Later there may have been further sanddeposition.
The debris-laden meltwater that flowed into valleys oftendeposited in them a considerable filling of sand and gravel. Somevalleys were filled to a depth of as much as 100 feet. Such depositsare called valley fills or valley trains. Modern streamshave cut their courses into many of these fills and even worn awaylarge parts of them. Remnants of valley train deposits are now largeterraces or benches along streams, many of them well above thepresent stream channels.
Where many small streams flowed from the glacier, theydeposited sand and gravel as a large apron in front of the glacier.Such deposits are called outwash plains and many of them extendfor miles.
Two other types of sand and gravel deposits made by glacialmeltwaters also are significant. One was formed where waterissued from the front of a glacier or poured into holes or crevassesin the ice. The sand and gravel in the water formed adeposit that now appears as a rounded hill associated with a terminalmoraine and is called a kame. The second type of depositwas laid down in beds of streams flowing under, through, or on theglaciers and was left as a more or less continuous ridge of sand andgravel when the ice melted. Such a deposit is called an esker.Some eskers in Illinois are about a quarter of a mile wide andseveral miles long. Typical are the Kaneville Esker northwest ofAurora, the Adeline Esker south of Freeport, and the Exeter Eskerwest of Jacksonville.
The deposits of both the Illinoian and Wisconsinan glaciersare widely distributed throughout the state. Melting of theIllinoian glacier caused comparatively little flooding; consequently,extensive gravel deposits were formed in only a fewplaces. The ice of the Wisconsinan glacier, however, meltedrapidly and produced great floods laden with sand and gravel.Thus, most major gravel deposits in Illinois are related to theWisconsinan glacier.
Wind sweeping across the sand and gravel deposits blewthe sand into hills or sand dunes near such places as Havana,Prophetstown, Kankakee, and Watseka. Even today the windshifts sand of long-forgotten glacial floods.
The foregoing discussion of glaciers and their deposits isgreatly simplified. For some time geologists of the Illinois GeologicalSurvey have been mapping the moraines, valley trains, outwashplains, and other glacial deposits of the state. Because theIllinoian and Wisconsinan glaciers advanced and retreated severaltimes, they built many moraines. The Survey has made a map(fig. 18) that shows the complexity of the moraines left by theWisconsinan glacier. They are roughly concentric, indicating thatthe general shape of the glacier front remained about the same.
The sand and gravel industry is widely distributed throughoutIllinois. The principal commercial sources of sand and gravelare valley trains and outwash plains. The Fox, Rock, Illinois,Mississippi, and Wabash Rivers and many smaller streams haveterraces in their valleys that are parts of valley trains. In thesedeposits are some of the largest sand- and gravel-producingoperations in the state.
An examination of glacial gravel deposits in Illinois revealspebbles and larger pieces of many kinds of rock. Some aregray, others white, pink, brown, or black. They commonly includelimestone, dolomite, granite, and many rocks with lesscommon names such as quartzite, schist, and basalt. The limestoneand dolomite were picked up by the glaciers from outcrops innorthern Illinois, Wisconsin, and Michigan. Some of the granitepebbles resemble outcrops in Wisconsin; others look like granitethat crops out in Canada. The quartzite probably came from Wisconsin,and black shale fragments found in some gravel depositscame from the floor of Lake Michigan or from western Michigan.Occasionally pieces of metallic copper are found that probablyhad their source in the Lake Superior copper-bearing area.
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 wereconstituents of rocks until weathering, the grinding action of theglaciers, and other erosive agencies broke the rocks into sand.The principal mineral in glacial sand is quartz, but many othersoccur in lesser amounts, including calcite, dolomite, feldspar,pyroxene, tourmaline, garnet, magnetite, and hornblende. Mostof these are foreign to Illinois, although the calcite and dolomitemay be native.
Figure 18—Moraines left by Wisconsinan glacier.
Figure 19—Gravel dredge, with plant for processing the gravel inbackground.
In 1963 more than 27 million tons of sand and gravel,directly or indirectly of glacial origin, was sold by Illinois producersfor almost 25 million dollars. The sand alone would havefilled a child’s sand box, with an area of 8 square miles, to a depthof 1 foot. The gravel would have covered an even larger area.
The gravel was used in making concrete for roads andbuildings, for surfacing roads, for ballast for railroad tracks, andfor other purposes. The sand found its way into plaster, mortar,concrete, and a variety of other products and uses. Some of it wasproduced for use as molding sand.
The production of sand and gravel from its deposits maybe a relatively simple operation or one of considerable complexity.Gravel for surfacing a road may be dug from a conveniently locatedpit and loaded mechanically into trucks that haul it to theroad. A large sand- and gravel-producing operation, however,may include not only mechanical equipment to load and transportthe material but also a processing plant where it can be washedif necessary and screened to various sizes.
In a “dry pit” operation, mechanical cranes or shovelspick up the gravel and sand and load it into trucks, railroad cars,or conveyor belts to be transferred to the processing plant. Thereclay and dirt may be washed out and the sand and gravel is sizedby screens. Conveyor belts carry sand and gravel to the variousprocessing operations and to storage bins or piles on the ground.
A “wet pit” operation produces sand and gravel from anartificial pond or lake. In some operations the sand and gravel ismined 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 ofgravel to wash the gravel into the lake. A large metal pipe at thefront of the dredge slants down into the water and sucks up the sandand gravel from the underwater part of the deposit. The gravel,sand, and water is then pumped through a pipe at the rear of thedredge to the processing plant on the shore.
In some types of wet pit operations a large scoop or bucketoperated from a crane on the shore, or by cables fastened to theshore, is used to dig sand and gravel from beneath the water.
Dredges are used to pump up sand and gravel from the bedsof Illinois rivers, especially the Mississippi, Ohio, and Wabash.
The sand and gravel resources of many parts of the statehave been mapped and studied by the Illinois Geological Survey,and work of this kind is continuing.
The hills of extreme southern Illinois contain severalmineral materials that are entirely or largely restricted, in importantquantities, to that part of the state. Some of them, such assilica and novaculite, come directly from bedrock deposits ofgreat age; others, such as some of the sands and gravels, are ofmore recent origin.
A mineral material unique in Illinois is the amorphoussilica, or tripoli, mined in the hills of southern Illinois about20 miles north of Cairo.
Most of the silica mines are found at the heads of valleysor in tree-covered hill slopes along the less traveled roads. Anarched opening (fig. 20) with a road leading into it may be all thatis visible of the mine from the outside. Inside are many rooms,33some 30 feet high, separated by rounded pillars about 20 feet thickthat have been left to support the arched mine roof.
Most of the silica in the mines is white, and this is thepart that is mined. A silica deposit is made up of layers—some ofwhite, powdery rock material, others that look chalky but are firmor hard.
Figure 20—Entrance to a silica mine.
In the mines the silica is blasted loose from the naturaldeposit and loaded into trucks that take it to the processing millsat Elco and Tamms, where it is crushed and then transferred tohuge grinding mills that pulverize it to a very fine powder. Aircurrents of different velocities separate the powder into variousgrades of fineness, and the finished silica goes into large paperbags for shipment.
Origin of Silica.—Some of the history of the formation ofsilica deposits is not fully known, but it seems probable that theiroriginal character was quite different from what it is today. Investigationsby Survey geologists suggest that the parent rock formationwas limestone and chert. The limestone was composed ofthe mineral calcite, but scattered through it were myriads of smallparticles of quartz. Interlayered with it were bands and beds ofchert that contained varying amounts of calcite.
As the rocks above them were worn away by the ceaselesserosion of streams and rivers, these original deposits were uncovered.Rain and snow-water then worked down into the limestoneand chert deposits through cracks and crevices and dissolved thecalcite in the rock. The quartz remained because it is much lesssoluble than the calcite. After many thousands of years all thecalcite had been removed, leaving behind a “skeleton” of quartz—thesilica deposits of today.
Uses of Silica.-The silica mined and milled in southernIllinois has many uses. A superfine grade, known as white rouge,is used to polish optical lenses. Other grades are used in scouringcompounds, metal polishes, paints, electrical resistors, high-temperaturepipe coverings, fiberglass manufacture, plastics,silicone rubber, wood filler, caulking compounds, ceramic products,floor tile, billiard cue chalk, as foundry parting or facing,concrete admixture, in the manufacture of buffing compounds thatare used to polish metal objects, and for other purposes. Industryuses many thousands of tons of silica each year.
Deposits of chert, chert gravel, and ganister also areamong the variety of mineral materials found in extreme southernIllinois. Chert consists principally of minutely crystalline particlesof quartz. Some chert is popularly called flint. In southernIllinois chert occurs in two principal kinds of deposits, thosecomposed of solid ledges and those consisting of gravel. Theterm novaculite is used in southern Illinois for those solid deposits35that are white, comparatively thick, and free of other interlayeredmaterials. No novaculite is mined at present, but it issaid to have been sold in past years for making sodium silicate andsilica brick.
The chert gravels of southern Illinois are of three kinds—novaculitegravel, Elco gravel, and “Lafayette” Gravel. The novaculiteand Elco gravels consist of fragments of chert plus lesseramounts of fine silica particles and clay. The chert fragments ofthe novaculite gravel are angular, but the Elco gravel includesboth angular and rounded fragments. These gravels are white,yellow, brown, or reddish brown, the novaculite gravel usuallybeing the more highly colored. Deposits in Union and AlexanderCounties have been used for road surfacing and other purposes.Deposits of chert gravel also occur in Hardin and Saline Counties,and some stream valleys in southern and western Illinois alsocontain such gravel.
“Lafayette” Gravel consists principally of brown chertpebbles. Most of the pebbles are rounded and have a smooth,semi-polished surface. The sand and clay occurring with thegravel are brown or dark red. In some places there are depositsof coarse, red quartz sand. The gravel is most abundant in thefour southernmost counties of the state, and deposits may be asmuch as 65 feet thick. It is used principally as a road-surfacingmaterial.
Ganister occurs in the hills of Alexander and Union Countiesand is a loosely consolidated, granular material consistingof irregular particles up to about an inch in diameter or of massesof material readily disintegrated into such particles. Theparticles are composed mainly of fine crystalline quartz. Ganisteris white, cream, light yellow, or red and occurs in depositsup to 25 feet or more thick. Relatively small tonnages of the lightcolored ganister are now used, principally in making refractories,but ganister is said to have been more widely used in that field inthe past. It is produced from underground mines. Some red ganister,or ganister like material, mined from open pits has been usedfor road surfacing.
Survey geologists have mapped the chert- and silica-bearingformations of Alexander and Union Counties and also manyof the various kinds of gravel deposits. Samples have been tested36to determine their chemical composition and the size of the particlescomposing them. Laboratory studies by ceramists indicatethat novaculite and novaculite gravel, when suitably processed,can be used for making silica brick, which withstands great heat.Canister and the gravels of southern Illinois offer a variety of rawmaterials awaiting increased industrial use.
In southern Illinois deposits of sand laid down in an armof the ocean that once extended northward into Illinois from theGulf of Mexico are found in Alexander, Union, Pulaski, Pope, andMassac Counties. The deposits are commonly a light color—white,cream, yellow, or gray.
The grains of the sand are almost all quartz and generallyare angular. Some of the sands are of almost powder-like fineness,others are fine or medium grained. Many of the sandscontain flakes of white mica, a glistening, silvery-looking mineraloften mistaken for silver or platinum. Unlike these metals,however, mica is comparatively light in weight and is not metallic.Also present in some sands are small flakes of the mineral graphite.
The southern Illinois sands have not been widely used,but some of them have been employed in making concrete. Theyalso may have possibilities for molding and core sand.
As a result of work by Survey geologists, the location andproperties of many of the southern Illinois sand deposits areknown.
Man has used clay in various ways for many hundreds ofyears. From it he made, and still makes, bricks to build hisdwellings, pottery utensils of many kinds, and other usefulproducts.
Everyone knows what clay is, yet it is a substance difficultto define. All clays are earth materials, most of them plasticor sticky when wet but firm when dry. If heated sufficiently(fired) they become hard.
Clays are composed of various minerals. Of these, theso-called clay minerals—complex substances composed mostlyof alumina, silica, and water—generally are the most important.They impart the property of plasticity and also cause clays tobecome hard when fired.
Most clays are what geologists call unindurated (unhardened)rocks. Clay that has been indurated and occurs in layereddeposits is commonly called shale. The layers may be from afraction of an inch to several inches thick. Most Illinois shalesare not plastic when dug from freshly exposed deposits, but theybecome plastic when crushed and kneaded with water. The claysand shales of Illinois are the basis of a huge and important industry.
Clays and shales are useful because they can be madeplastic by adding water, formed into desired shapes, and fired toa rock like hardness. As a result, various kinds of bricks, draintile, pottery, and other useful products are made from them. In itsearly years, Illinois had many widely distributed potteries thatused clay from nearby deposits to make a variety of jugs, crocks,and bowls that served in place of many present-day glass or metalarticles.
Drain tile has been of major importance in the developmentof the state. Early settlers found many low lying, swampy areasand tracts of land that drained poorly after heavy rains. Ditcheswere dug to carry away the water from some areas, but others weredrained by means of drain tile—pieces of fired clay pipe severalinches in diameter and about a foot long that were laid end to endin trenches below plough depth and then covered with earth. Waterseeped into the tile, which discharged it into ditches. Tile factories,built throughout Illinois near clay or shale deposits, didan active business. Gradually, however, as more and more farmland was drained the demand slackened and many tile factorieswent out of business. Although there are fewer factories, muchdrain tile is still manufactured in Illinois.
Many of the early tile plants also made bricks to be usedfor making foundations, buildings, sidewalks, and other structures.The bricks were made by hand-operated equipment. Someof the old hand-molded bricks may still be seen in older buildings.Now the brick-making process is highly mechanized and eventhough there are fewer plants they produce more bricks.
Illinois shales are a part of the bedrock—that is, theyare associated with indurated rocks such as sandstone and limestone.Most clays are surficial rocks occurring in deposits nearthe surface, where they lie above the bedrock. Exceptions are38certain clays found in extreme southern Illinois and the underclays,also called fireclays, that occur beneath coal seams andare part of the bedrock.
The surficial clays are of two principal kinds—till andloess. Till is a deposit left by glaciers. It is a gray, blue-gray,or brown clay containing varying amounts of sand, pebbles,cobbles, and even boulders. Till is found at many places in thestate and is used for brick making, especially in the Chicago area.
Loess is a wind-deposited silty clay or clayey silt andis found in many parts of Illinois. It is thickest on or near thebluffs of the Mississippi, Illinois, and Ohio Rivers. It generallyis brown and stands in steep faces in roadcuts and other excavations.It once was widely used for making brick and tile.
Of major importance in making clay products in Illinoisare the bedrock shales and the clays associated with the coal-bearingrocks that underlie much of the state. The shales, and theclays to a lesser extent, are dug at many places for makingstructural clay products such as bricks, structural tile, and draintile. They also are used to make lightweight aggregate for concrete.The underclays of some of the older coal seams are usedto make buff-colored brick, stoneware, and a highly heat-resistantbrick (firebrick) that is used in industrial furnaces or in other operationsinvolving high temperatures. Some fireclay, ground as fineas flour, is added to molding sand to make it coherent enough toform into molds for metal casting. Sewer pipe and flue lining alsoare made from underclays.
Clays unlike those found elsewhere in the state occur inextreme southern Illinois. One of these has the property of removingcolor from oils and was so used at one time by petroleumrefineries. Another, kaolin, was extensively used during WorldWar I for making crucibles.
The uses of clay and shale are determined to a large degreeby the properties of their clay minerals and to a lesser degree bythe impurities present. A clay or shale containing the clay mineralillite, and other similar but less important clay minerals, commonlybecomes red when fired and gets hard at a relatively low temperature.It therefore is used to make red bricks, drain tile, buildingtile, and other structural clay products.
Another clay mineral, kaolinite, generally burns to alight color and is difficult to fuse. Therefore, clays composedwholly or mainly of kaolinite can be used for making buff or light-coloredbricks and for the manufacture of highly heat-resistant(refractory) bricks.
The clay mineral in the southern Illinois clay that was usedto decolorize oil is montmorillonite. This clay is now used insweeping compounds, as an oil absorbent, as animal litter, andfor other purposes.
In view of the significant relationship between the clayminerals and the utilization of the clays and shales in which theyoccur, the Illinois Geological Survey has investigated extensivelythe clay minerals in the clay and shale deposits of Illinois. Manysamples were studied by means of powerful microscopes, X-ray,and chemical analysis. Most of the surface clays and shalesproved to be composed principally of illite or related minerals.The kaolin clay of extreme southern Illinois contains the mineralkaolinite. The older underclays also contain kaolinite, but manyof them also contain smaller amounts of illite.
The Survey also has tested many clays to determine theirburning properties and color when fired, and hence their potentialuses. The bonding capabilities of other clays have been measuredto find out whether they can be used as a bonding material formolding sand. The bloating properties of Illinois clays and shalesfrom many deposits have been studied to determine which aresuitable for making lightweight aggregate for the manufacture ofconcrete.
The object of these studies has been to discover the location,character, and possible uses of the state’s clay and shaleresources. Special studies are continuing in several parts of thestate. Illinois is well endowed with clays and shales that can beused for a variety of purposes and has resources to fill future aswell as present needs.
Conversion of Illinois clays and shales into useful productsis an interesting process and is exemplified by the making of buildingbricks. Mechanical shovels dig the clay or shale and load itinto trucks or small railroad cars that take it to the brick plant.There, machines grind the raw material and mix water with it untilit has the consistency of stiff mud.
Next, a machine, which operates somewhat like a meatgrinder, extrudes a brick-sized column of clay. As the columnmoves forward, it is automatically cut into bricks by wires. Thebricks are then dried in large heated rooms.
Figure 21—Beehive brick kiln.
From the driers, the bricks go to huge ovens (kilns) andare heated until they are hard and have attained the desired color.This is known as firing or burning the bricks. Temperatures employedare rarely lower than 1800° F.
Three kinds of kilns are used in Illinois for burning bricks—beehive,tunnel, and scove. A beehive kiln (fig. 21) has a roundbase and a dome-shaped top and somewhat resembles an oversizedbeehive. Unfired bricks are stacked in the kiln and the doors aresealed with burned bricks and clay. Fires are started in hearthsor fire boxes in the wall of the kiln and the heat is circulated intoand through the kiln. It usually takes several days to fire the bricksadequately and let the kiln cool so that the bricks can be removed.
Tunnel kilns, made from heat-resistant bricks, are actuallytunnels big enough for a man to stand in. The unburned bricks areloaded on flat steel cars on top of a layer of refractory blocks thatprotect the steel from the heat. The cars enter the kiln and heatingbegins. As they move through the kiln, they carry the bricksthrough a firing area, then through a cooling zone, and finally outinto the air.
In some brickyards in the Chicago area, dried unburnedbricks are carefully stacked by machines into piles about 17 feet41high, 35 feet wide, and 115 feet long, which are known as scovesor scove kilns. A layer of burned bricks that is plastered with claycovers the sides of the scove. A jet of flame is directed throughsmall tunnels at the base of the scove, and the heat fires the bricks.
During 1963, more than 325,000,000 bricks were producedby Illinois brick plants. In the same year, the value of all theclay and clay products produced in Illinois was nearly $54,000,000.Besides brick and drain tile, the products of the clay and shale industryof Illinois include refractory brick, building block and tile,fire-proofing, sewer pipe, flue liners, stoneware, lightweightbloated burned clay aggregate for concrete, and a variety of unburnedclays for special purposes, including bonding clay, refractoryfireclays, absorbent for use on garage floors, and litterfor animal cages.
After the retreat of the last of the great ice sheets fromIllinois, numerous ponds and lakes were left in northern Illinois,especially in the eastern section. Some of them were soon drainedby natural processes, but others remained. In the shallow wateralong their shores grew various plants, chiefly reeds and sedgesand, locally, a variety of moss. As the plants died, their partiallydecomposed remains were preserved beneath the water. Ultimately,the ponds and lakes were overgrown and more or less completelyfilled by the plants and their remains, giving rise to peat (fig. 22)bogs.
Some peat bogs have been drained and are now used asfarm land. Others remain and a few of them are the source of peator humus for horticultural purposes. Producing operations are locatedin northeastern Illinois and in Whiteside County in northwesternIllinois.
In the future, new uses will be made of the Illinois industrialminerals already discussed. In addition, other mineral resourcesof the state that are not now being used may be the basesof new mineral industries. Some of these minerals are at presenttoo costly to mine because the deposits are deeply buried or are42not sufficiently rich to be worked at a profit. Others are not convenientto markets, and still others have no present commercialuse. In years to come, however, changes may occur that will makeit practical to mine, process, and use some of these resources.Furthermore, some other mineral deposits that are now being utilizedin a limited way may have greater future use. The IllinoisGeological Survey continues to study the location, character, andcomposition of many such mineral materials and is alert for thedevelopment of new uses. Some of the materials are discussedbriefly below.
Figure 22—Peat from Kane County showing its fibrous nature andremains of plants.
Gypsum is a mineral that consists of calcium sulfate plustwo molecules of water (CaSO₄·2H₂O). By suitably heating it, theamount of water can be reduced, and a product called calcinedgypsum (plaster of paris) results. This material changes back togypsum if mixed with an appropriate quantity of water. The abilityof calcined gypsum to “set” when water is added makes it43important in the manufacture of a variety of plasters and relatedproducts, especially building materials. Gypsum also is used incement making and in agriculture.
Anhydrite (CaSO₄) is like gypsum except that it containsno water and hence cannot be made into plaster of paris. Its usesare limited in the United States.
Wells that were drilled for oil, water, or coal have encounteredgypsum and/or anhydrite in some parts of south-centralIllinois, but the gypsum and anhydrite are not known to crop outat the surface. A study of diamond drill cores and well cuttingson file at the Survey showed that the shallowest gypsum and anhydritereported occurred at a depth of 470 feet in Madison County.The greatest continuous thickness of gypsum found was 2 feet;but in one well, over 6 feet of strata was penetrated that averagedalmost 75 percent gypsum. It is possible that thicker deposits ofgypsum might be found if drilling were done especially in searchof it.
Feldspar is the name applied to a group of minerals thatare mainly silicates of potassium, sodium, and calcium. Variouskinds of feldspar are used industrially in making glass, enamels,pottery, and other products. All the feldspar now used in Illinoisis shipped into the state. The discovery by the Illinois Surveythat some Illinois sands contain considerable feldspar led Surveygeologists and chemists to find where deposits highest in feldsparoccur, what kinds of feldspar they contain, and whether it couldbe separated from the sand in which it occurs. Beach sands, riversands, dune sands, and sands from other kinds of deposits werestudied.
It was found that many sands contain more than 15 percentfeldspar and some as much as 25 percent. Means of separatingthe feldspar from the sand are believed to exist, but problems relatingto the purity of the separated spar remain to be solved.
No salt is now produced in Illinois, but at one time thestate was a major salt producer. Salt works were in operationnear Equality, Central City, Murphysboro, St. John, Danville,and possibly other places. The salt was obtained by evaporatingsalt water (brine) that came from natural springs or from wells.The Equality area was a particularly important producer of salt in44the 1800’s. Discovery elsewhere in the Middle West of depositsof rock salt and brines that contained more salt than those of Illinoisis said to have been responsible for the discontinuance ofsalt making in the state.
No salt beds crop out in Illinois, nor are any known tohave been encountered in the many wells that have been drilled forcoal, oil, or water. However, most oil well drilling encountersbrines containing various amounts and kinds of salts, includingthe common table salt, sodium chloride.
For reasons relating to the production of oil, Survey geologistsand chemists have collected and analyzed many samples ofIllinois oil field brines, and data are therefore available on theirsalt content. No commercial use is being made of the brines assources of salt.
Illinois has a large oil-producing industry that obtains oilfrom wells. The state also contains beds of shale that yield oilwhen the shale is heated.
In order to estimate the present and future importance ofthe oil shale resources, the Survey collected and tested more than100 shale samples from 41 Illinois counties. A few samples containedmore than 25 gallons of oil per ton of shale, but most containedless than 15 gallons per ton. A study of the crude oil distilledfrom selected shale samples showed it to be somewhat differentfrom the oil that comes from wells. It could, nevertheless,be made to yield gasoline, fuel oil, and other products if suitablyprocessed.
The shale strata generally the richest in oil are found abovecoal seams, are black, and are sometimes called slate by coalminers. They are rarely more than 3 feet thick, but they extendover large areas.
Sandstone has a long history of use in Illinois. Pioneersbuilt foundations for their houses and barns and curbs around theirwells from it. Slabs of sandstone were once a popular materialfor sidewalks, some of which are still in use. Churches and othersizable buildings have been constructed from it, and at one timean Illinois sandstone was used to make grindstones. Except forthe St. Peter Sandstone, which was discussed under “Silica Sand,”the use of sandstone has decreased, although comparatively smallquantities are still used as building stone.
Most Illinois sandstones may be thought of as a mass ofsand whose grains are more or less firmly cemented together byclay, iron oxide, and quartz, either singly or in combination, or,less commonly, by calcite. The grains are particles of variousminerals, but most of them are quartz.
Sandstones are especially common in the hill country ofextreme southern Illinois. The Survey’s investigations in this arearevealed that if they are suitably processed some of the sandstonesmay have possibilities for commercial use. Sandstones in otherparts of the state also have been studied, with similar conclusions.
Barite (barium sulfate, BaSO₄) is a deceptive mineral—it ismuch heavier than it looks. Barite found in Illinois is generallywhite or light colored, and, although some of it looks rather likewhite limestone, it is more than half again as heavy as limestone.Barite’s unusual weight is responsible for one of its major uses—asa constituent of drilling muds for the oil industry. These mudsare a mixture of clay, water, and a weighting material such asbarite. They are used in various ways in the drilling of oil wellsby rotary drills. Barite also is an important raw material for themanufacture of chemicals.
Barite is found in Hardin and Pope Counties, the site ofthe fluorspar industry. According to studies made by Survey geologists,the barite occurs both as veins and beds associated withfluorspar, but its distribution is irregular and the deposits are oflimited size. A barite mine is said to have been worked years ago,and more recently comparatively small tonnages have been takenfrom open pits. Future exploration in southern Illinois may revealdeposits of barite that will be profitable to mine.
In some parts of Illinois occur sands or sandstone thatcontain numerous grains of the green mineral glauconite. If thesands are not discolored by iron compounds or other substances,they too have a greenish color and, therefore, are called greensands.Glauconite varies in composition but contains potassium,magnesium, iron, aluminum, silicon, and water. Greensand issaid to be used in relatively small amounts as a soil conditionerand as a water-softening agent.
Greensand is known to occur in the general vicinity ofOlmsted in southern Illinois. Near Oregon in northern Illinois anold quarry exposed 10 feet of greenish brown sandstone that containsglauconite. Samples from southern Illinois and from the sandstoneat Oregon contained more than 6 percent potassium oxide.
In some of the lakes and ponds left by the glaciers livednumerous small mollusks with calcium carbonate shells. As theanimals died, their shells formed a deposit on the bottom of thelakes and ponds. Certain plants, especially algae, may haveadded a mudlike precipitate of calcium carbonate to the deposits,and varying amounts of clay washed from the shores mixed withboth these materials. The resultant deposit is called marl. Somemarl deposits have peat mixed with them, and peat also overliessome marl deposits.
Only comparatively small amounts of marl are known tohave been dug in Illinois. One deposit containing many shells andshell fragments, some of it associated with peat, was worked insoutheastern Livingston County as a source of agricultural limingmaterial. Other deposits have been reported at other places innortheastern Illinois. The available information indicates that themarl deposits are likely to be principally of local importance.
The tufa (fig. 23) and travertine occurring as surficial depositsin Illinois were formed by springs. The deposits usuallyoccur at or near the outcrop of a layer of porous water-bearingearth material, such as gravel, sandstone, or fissured limestone,that is underlain by a nonporous clay or shale formation. Watermoving down through the porous layer cannot sink through the clayor shale and so is forced to move laterally. Where valleys havecut into the layers of gravel or rock, the water emerges as springs.
If the material through which the water has passed is limestone,or gravel containing limestone as most Illinois gravels do,some of the limestone is likely to have dissolved in the water.When the water issues as a spring, conditions may be such as tocause precipitation of the dissolved limestone as tufa or, morerarely, travertine.
Tufa is generally highly porous and more or less impure,whereas travertine is harder and less porous.
The middle or lower slopes of bluffs are common sites forspring-deposited tufa or travertine. Deposits have been seen invarious parts of Illinois, but are not known to have been worked,except in Calhoun County where small quantities of tufa were producedfor use as agricultural limestone. It is thought that the tufaand travertine deposits of Illinois are relatively small, but theymay be of local importance.
Figure 23—Calcareous tufa from Pike County. In addition to thelarge visible pores there are numerous tiny ones.
The mineral pyrite consists of iron and sulfur as the compoundiron sulfide (FeS₂) and, because of its shiny, brassy yellowcolor, is sometimes called fool’s gold. Marcasite has the samecomposition as pyrite, but its crystals have a different shape andit is often lighter colored. Both minerals occur in various partsof the state; they are particularly prevalent in some coal seams,and when so occurring are in some cases called coal brasses or“sulfur.”
Pyrite and marcasite are used commercially as raw materialsfor making sulfuric acid, although sulfur itself is more extensivelyused for that purpose. At one time coal brasses recovered duringcoal-cleaning operations at a northwestern Illinois coal mine weresold for acid making. A large quantity of coal brasses probablycould be recovered from such operations at Illinois coal mines.
Uranium has been sought in Illinois by many people inrecent years. The Geological Survey also carried out a wide searchfor uranium and particular attention was paid to certain clays andother rocks in Hardin County and certain black shales in other partsof the state.
About 200 samples from Hardin County and 175 samplesof the shales were tested by the Survey. No deposits were foundthat are known to be of the required richness and quantity.
About the middle of the 19th century two furnaces in HardinCounty in extreme southern Illinois for a time produced iron fromlocal limonite ores. The ore is said to have occurred as pellets,chunks, and masses scattered through soil and clay and apparentlywas of irregular distribution. Little can be seen of the depositstoday. Their extent is not known, but they are believed to be oflimited size.
The Illinois State Geological Survey carries on acontinuous program of research on the industrial mineralsand metals of Illinois and their uses.
In addition to the investigations mentioned in thisbooklet, many others have been made or are in progress.Such studies are necessarily a continuing activity if thefull potentialities of Illinois mineral resources are to berealized, for industry continually demands new raw materialsand changes its requirements for those now used.
The Survey has issued numerous reports that dealwith the resources discussed here and mimeographed listsof these are available upon request.
If reproduction is made of the material herein,acknowledgment of the Illinois State Geological Surveyis requested.
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