,educational ,series #e ,guide to ,,rocks ,,and ,,minerals ,,of ,,illinois ,illinois ,state ,geological ,survey ,illustration3 uncaptioned ,,state of ,,illinois ,william ,g4 ,stratton1 ,governor ,,department of ,,registration and ,,education ,vera ,m4 ,binks1 ,director ,first printing #aiei ,second printing #aifj ,,illinois ,,state ,,geological ,,survey ,john ,c4 ,frye1 ,chief ,,urbana1 ,,illinois ,printed by ,authority of the ,state of ,illinois ,guide to ,,rocks ,,and ,,minerals ,,of ,,illinois ,illinois has so long been known as the ,prairie ,state that at first glance it seems a most unlikely place in which to collect rock and mineral specimens4 ,but ,illinois has a surprising wealth of rock and mineral resources1 not only to be collected as interesting specimens but to be put to practical and profitable use4 ,the rich prairies that gave the state its nickname are themselves derived from ancient rocks1 worn and changed by millions of years of action by weather1 water1 wind1 plants1 and animals4 ,unmeasured depths of rock underlie the prairies1 hills1 and valleys1 and in some parts of the state are exposed in outcrops1 canyons1 and river valleys4 ,boulders and gravel brought in by the glaciers thousands of years ago are strewn over many parts of the state4 ,these resources are of great value4 ,besides the rich agriculture based on the rock-derived soil1 much of our industry1 manufacturing1 and transportation is dependent on rock and mineral materials4 ,every county in ,illinois possesses some rocks and minerals that either are being used or have potential future value4 ,the ,illinois ,state ,geological ,survey several years ago began to prepare sets of typical rocks and minerals of ,illinois for use by the schools and other educational groups in ,illinois4 ,this booklet is designed to furnish a brief geological background and explanation of these common ,illinois rocks and minerals4 ,it also should be useful to the student or amateur interested in making his own collection4 ,even though ,illinois has no mountain ranges or deep canyons1 the geology of the state has many complexities4 ,in fact1 the very flatness of our topography is a complicating factor because in order to study the geology at many places in the state it is necessary to use information from mines and descriptions 7logs7 and samples 7cores7 of the rock penetrated during drilling of deep wells4 ,there are also geophysical methods of learning something about the rocks beneath the surface4 ,illustration3 ,fig4 #a4--;,geologic map of ,illinois4 ,,cambrian ,,ordovician ,,ordovician-,,silurian ,,ordovician-,,silurian ,,under ,,drift ,,devonian-,,mississippian ,,pennsylvanian ,,under ,,drift ,,cretaceous-,,tertiary ,,key ,wisconsin glacial drift ,illinoian glacial drift ,pennsylvanian boundary ,the complexity of ,illinois geology is not produced by the upturning and sharp folding of rock layers such as can be seen in the ,rocky ,mountains1 but rather by the changes in composition1 thickness1 and character of the rock layers that are only gently warped or relatively flat4 ,at several places in the state1 especially in the southern part1 faults1 or breaks1 in the rock layers do occur1 but over much of our area this is not common4 ,the presence of usable minerals at considerable depth is known at many places2 coal is mined from depths greater than #hjj feet1 and oil is produced from saturated rock layers1 called pay zones1 several thousand feet below the surface4 ,lead and zinc ores1 fluorspar1 silica sand1 limestone1 sand1 gravel1 clay1 and shale are all produced at shallower depths4 ,however1 the student can see only those rocks and minerals that are to be found at or near the surface4 ,for that reason the following paragraphs describing their geologic occurrence deal only with surface geology4 ,the youngest of the major geologic divisions of our rocks is called the ,pleistocene1 which is the scientific name for the 8,ice ,age0 deposits4 ,during this relatively recent period of geologic time1 which began about a million years ago1 glaciers flowed southward from ,canada and spread a layer of 8glacial drift0 over all of the state except the northwest corner1 the southwest edge of the state along the ,mississippi ,river1 and extreme southern ,illinois 7fig4 #a74 ,most of the glacial deposits that we see were formed by the last two of the four major periods of glacial advance1 the ,illinoian and the ,wisconsin4 ,the ,illinoian was the most extensive1 reaching as far south as ,carbondale and ,harrisburg4 ,the ,wisconsin1 so called because its deposits are so widely spread in that state1 reached only to ,mattoon and ,peoria4 ,the glacial drift is the youngest and uppermost of the divisions of the rock column 7fig4 #b74 ,within the drift can be found the widest diversity of rock and mineral types--quartzite1 schist1 and other metamorphic rocks2 granite1 gabbro1 and other igneous rocks2 and of course the sedimentary rocks1 limestone1 dolomite1 sandstone1 shale1 and even pieces of coal1 which occur in bedded layers of the older rocks in ,illinois4 ,sand and gravel were carried and deposited by flowing streams before1 during1 and after glaciation1 but the major deposits were made while the glaciers were melting4 ,they contain a wide variety of rock and mineral types4 ,illustration3 ,figure #b--;,diagram of layers of rocks in ,illinois4 ,era ,general ,types of ,rocks ,period or ,system and ,thickness ,epoch ,,cenozoic 8,recent ,life0 ,age of ,mammals ,quaternary #j-ejj ,pleistocene or ,glacial ,age ,recent--alluvium in river valleys ,glacial till1 glacial outwash1 gravel1 sand1 silt lake deposits of clay and silt1 loess and sand dunes2 covers nearly all of state except northwest corner and southern tip ,tertiary #j-ejj ,pliocene ,chert gravel2 present in northern1 southern1 and western ,illinois ,eocene ,mostly micaceous sand with some silt and clay2 present only in southern ,illinois ,paleocene ,mostly clay1 little sand2 present only in southern ,illinois ,,mesozoic 8,middle ,life0 ,age of ,reptiles ,cretaceous ,mostly sand1 some thin beds of clay and1 #j-cjj locally1 gravel2 present only in southern ,illinois ,,paleozoic 8,ancient ,life0 ,age of ,amphibians and ,early ,plants ,pennsylvanian ,largely shale and sandstone with beds of coal1 #j-c1jjj limestone1 and clay 78,coal ,measures07 ,mississippian ,black and gray shale at base2 middle zone of #j-c1ejj thick limestone that grades to siltstone1 chert1 and shale2 upper zone of interbedded sandstone1 shale and limestone ,age of ,fishes ,devonian ,thick limestone1 minor sandstones and shales2 #j-a1ejj largely chert and cherty limestone in southern ,illinois ,age of ,invertebrates ,silurian ,principally dolomite and limestone #j-a1jjj ,ordovician ,largely dolomite and limestone but contains #ejj-b1jjj sandstone1 shale1 and siltstone formations ,cambrian ,chiefly sandstones with some dolomite and shale2 #a1ejj-c1jjj exposed only in small areas in north-central ,illinois ,,archeozoic and ,,proterozoic ,igneous and metamorphic rocks2 known in ,illinois only from deep wells ,as shown by the diagrammatic rock column 7fig4 #b71 rocks placed in the divisions called early ,cenozoic and ,mesozoic are next in age to the ,pleistocene4 ,the map 7fig4 #a7 shows that the ,cenozoic and ,mesozoic rocks occur only in the extreme southern tip of ,illinois because only that part of ,illinois was covered by a northward extension of the forerunner of the ,gulf of ,mexico in which the deposits of sand1 gravel1 and clay were laid down4 ,the next older division of ,illinois rocks is called ,pennsylvanian--or 8,coal ,measures0--because during the last century they were first extensively described by geologists working in ,pennsylvania4 ,the ,pennsylvanian is one of our most important groups of rock strata because it contains all of our minable coal beds1 as well as important deposits of limestone1 shale1 clay1 sandstone1 and some oil and gas4 ,the ,pennsylvanian rocks are very widespread in ,illinois1 occurring under the glacial drift from depths of a few feet to several hundred feet throughout about two-thirds of the glaciated area 7fig4 #a74 ,next below the ,pennsylvanian are the ,mississippian rocks4 ,we in ,illinois are particularly interested in this division of rocks because they take their name from the excellent exposures along the ,mississippi ,river valley in western ,illinois1 southeastern ,iowa1 and eastern ,missouri4 ,they are composed of extensive beds of limestone and cherty limestone1 sandstone1 and shale4 ,mississippian rocks are of great economic importance in the structural area known as the ,illinois ,basin1 where they are the most important oil producing rocks4 ,they also contain our fluorspar deposits and along the valley bluffs are an excellent source of limestone for quarrying4 ,rocks older than the ,mississippian--except for small areas along the ,mississippi and ,illinois ,river valleys--are found at the surface only in the northern quarter of the state and locally in ,hardin ,county near the southern tip of the state4 ,they are nonetheless economically important because from these older rocks are produced lead and zinc1 some oil and gas1 silica sand1 limestone1 dolomite1 and shale4 ,on the generalized rock column 7fig4 #b7 these older rocks are grouped into two units4 ,the uppermost contains the ,devonian and ,silurian and the lower contains the ,ordovician and ,cambrian4 ,in general they include dolomite1 limestone1 and shale1 with sandstone at several places1 especially in the lower unit4 ,,description ,,of ,,rocks ,,and ,,minerals ,the terms mineral and rock are often confused4 ,they are frequently used together and the materials they describe are closely related4 ,in general1 a mineral is a naturally occurring chemical element or compound formed by inorganic processes1 whereas a rock is a mixture of particles or grains of several minerals4 ,however1 when we refer to mineral resources or industrial minerals1 we generally include materials that are technically rocks--such as limestone1 dolomite1 shale--and also coal and oil that are in fact organic substances4 ,on the other hand1 we include in the rock category high purity sandstone that is composed almost entirely of one mineral 7quartz7 and high purity limestone that is composed largely of the mineral calcite4 ,,minerals ,a few minerals are composed of only one element1 such as diamond 7carbon7 and native copper1 but most minerals are chemical compounds that contain several elements4 ,most minerals grow into distinctive shapes if they are free to grow4 ,a familiar example is the formation of salt crystals that grow on a saucer of evaporating salt water4 ,the distinctive shapes of crystals are called their habits1 and the flat surfaces that develop are called crystal faces1 the angles of which may be used to identify the mineral4 ,the individual atoms of a crystal always arrange themselves in the same way1 so that each mineral breaks characteristically4 ,some minerals break more easily in particular directions and present a flat1 smooth surface4 ,this characteristic is called cleavage and the cleavage surfaces1 although sometimes confused with crystal faces1 may be useful for identifying a particular mineral4 ,the manner in which a mineral breaks when the broken surface does not include cleavage surfaces is called its fracture1 and this too may give a clue to the identification of the mineral4 ,there are other physical features useful in identifying minerals4 ,some of them1 such as color1 are quite obvious4 ,the color of the powder left when a mineral is scraped on a rough1 white surface1 such as unglazed porcelain or tile1 is called streak4 ,luster refers to the brightness of light reflected from the mineral's surface4 ,transparency and translucency refer to the mineral's ability to transmit light1 and tenacity is a measure of its toughness4 ,two special physical characteristics of minerals are important to their identification--specific gravity and hardness4 ,specific gravity simply means the ratio of the weight of the mineral to an equivalent volume of water4 ,for example1 if a mineral has a specific gravity of #d1 then a cubic inch of the mineral weighs as much as #d cubic inches of water4 ,hardness is measured by the ability of one mineral to scratch another1 and a set of ten standard minerals has been selected for determining this characteristic4 ,the listing below1 from soft to hard1 is known as ,mohs scale4 #a--,talc #b--;,gypsum #c--;,calcite #d--;,fluorite #e--;,apatite #f--,orthoclase #g--,quartz #h--,topaz #i--;,corundum #aj--;,diamond ,a rough measure of hardness can be made by using handy objects4 ,your fingernail has a hardness ranging from #b to #c1 a penny is a little harder than #c1 window glass ranges from less than #e to approximately #f in hardness1 and a knife blade is generally in the range of #e to #f4 ,,rocks ,rocks1 being mixtures of minerals1 are more complex than minerals and are therefore classified in a more complicated way4 ,the broadest grouping of rocks is based on the origin of the rock rather than on the minerals that compose it4 ,in this scheme all rocks are divided into three general groups1 igneous1 sedimentary1 and metamorphic4 ,the igneous rocks are mentioned first because they are produced directly from hot liquids that come from deep within the earth4 ,these hot liquids are essentially molten rock and are called magmas4 ,when they cool1 the elements of the individual minerals come together and crystallize1 as water crystallizes into ice on a winter day4 ,different minerals crystallize1 or 8freeze01 at different temperatures so that if the magma cools slowly some individual grains have opportunity to grow larger than others4 ,if the magma cools quickly1 as does lava or basalt1 the separate mineral grains will be small4 ,igneous rocks are classified on the basis of the size and arrangement of the individual crystals and the kinds of minerals present4 ,the glacial drift in ,illinois contains many pieces of igneous and metamorphic rocks1 but most of the rocks native to ,illinois are sedimentary4 ,some sedimentary rocks are made up of weathered fragments of other rocks that have been moved by rivers1 waves1 winds1 or glaciers4 ,these sediments have been deposited and later compacted or cemented by the mineral matter carried in water moving through them4 ,such sedimentary rocks are called clastic 7meaning broken pieces7 rocks1 as opposed to those formed by chemical precipitation from water and those that consist of fossil remains4 ,clastic sedimentary rocks are classified first on the basis of the size of the grains of gravel1 sand1 silt1 and clay of which they are composed2 on the type of deposition1 such as glacial drift and wind-blown silt or loess1 that produced them2 and then on the basis of their mineral composition4 ,rocks such as gypsum and some of our limestones were formed by chemical precipitation from sea water4 ,metamorphic rock literally means rock that has changed form4 ,the change of form has been caused by heat and pressures that occur below the surface of the earth or by heat from upward moving hot magmas or melted rocks4 ,examples of metamorphic rocks are found in ,illinois as boulders and pebbles in the glacial drift4 ,descriptions of the rocks and minerals represented by specimens in the ,geological ,survey's rock and mineral sets follow4 ,the numbers preceding the descriptions correspond to the numbers on the specimens in the sets4 ,although the set includes the rocks and minerals that are most commonly found in ,illinois1 many others can be collected4 ,for that reason1 following the descriptions is a key for identifying other ,illinois minerals and rocks4 ,as a further aid to the beginner and the amateur1 a list of equipment useful in making a rock and mineral collection is given at the end of the book4 ,,granite 7#a7 ,,granite is one of the most widespread intrusive 7originating deep within the earth7 igneous rocks4 ,it consists chiefly of feldspar and quartz with small amounts of biotite1 muscovite1 or hornblende4 ,most granite is light colored1 but it can be white1 gray1 yellow1 pink1 or deep red4 ,the texture ranges from medium grained to coarse grained4 ,granite pebbles or boulders are the most common igneous rocks found in glacial deposits in ,illinois4 ,they are not native to the state but were brought here by the great ice sheets or glaciers that advanced from southern ,canada to cover much of northern ,united ,states during ,pleistocene time4 ,native granitic rock probably lies very deep beneath the entire state4 ,it has been found in deep oil-test drillings along the western and northern margins of ,illinois4 ,,gabbro 7#b7 ,,gabbro is another intrusive igneous rock1 but it is heavier and darker than granite4 ,it is composed mainly of feldspar and dark iron-bearing minerals that give the rock a dark color4 ,it is coarse grained and contains little or no quartz4 ,mineral crystals of gabbro are especially tightly interlocked1 making the rock very difficult to break4 ,weathered gabbro is a rusty color on the surface1 because the iron in gabbro changes color just as a piece of metallic iron becomes coated with rust when left out of doors4 ,like other igneous rocks found near the surface in ,illinois1 gabbro was carried into ,illinois by the glaciers and deposited as glacial debris4 ,,porphyry 7#c7 ,,porphyry is an igneous rock identified by its texture rather than its mineral content1 which is variable4 ,distinct crystals 7phenocrysts7 of minerals are embedded in a matrix of fine-grained rock4 ,the phenocrysts formed before the main mass of the rock hardened4 ,any igneous rock may have a porphyritic variety1 such as granite porphyry and rhyolite porphyry1 although porphyries are most likely to form in association with fine-grained igneous rocks4 ,porphyry is found in ,illinois only in glacial drift4 ,,basalt 7#d7 ,,basalt is the most widely distributed volcanic rock4 ,pyroxene1 feldspar1 magnetite 7an iron ore71 and in some instances olivine1 biotite1 and hornblende1 compose this rock4 ,the dark green1 gray1 or black color is due to the dark-colored minerals that make up much of the rock4 ,the minerals in basalt are fine grained and are packed closely together4 ,phenocrysts of olivine1 pyroxene1 and hornblende may be present4 ,basalt is easily identified by its color and fine-grained texture4 ,the glaciers brought basalt into ,illinois along with other igneous rocks4 ,,peridotite 7#e7 ,,peridotite is the only igneous rock native to ,illinois that crops out at the surface4 ,it is found as dikes 7irregular veins7 or sills 7thin sheets7 that were formed when molten rock from deeper in the earth intruded into cracks and fissures in the bedrock of southeastern ,illinois 7,hardin1 ,pope1 ,gallatin1 and ,saline ,counties74 ,peridotite pebbles and boulders also may be found in the glacial drift4 ,peridotite ranges from very fine grained to medium grained and has an even texture4 ,it is dark gray to greenish gray1 depending on the minerals present4 ,in general it is composed of olivine1 hornblende1 pyroxene1 and mica1 with little or no feldspar or quartz4 ,,gneiss ,,and ,,schist 7#f7 ,,gneiss is a metamorphic rock composed of roughly parallel bands of minerals4 ,it is medium grained to coarse grained and is generally light in color4 ,the names given to gneiss emphasize a distinctive texture or mineral or indicate composition4 ,for example1 biotite gneiss emphasizes a mineral1 and granite gneiss indicates the composition of the rock4 ,,schist is much like gneiss but is fine grained and has a thinly layered structure that makes the rock break with a wavy surface4 ,some common types of schistose rocks are talc schist1 chlorite schist1 and hornblende schist4 ,as the names indicate1 they are characterized by their dominant mineral4 ,mica schist may be formed by the metamorphism of either sedimentary or igneous rocks4 ,gneiss and schist are not native to ,illinois but are found in the glacial drift4 ,,conglomerate 7#g7 ,,conglomerate is a sedimentary rock made up of pebbles or other rock fragments cemented in a background or matrix of finer material1 generally silica1 calcium carbonate1 clay1 iron oxide1 or a mixture of these substances4 ,the rounded rock fragments have been worn by being rolled in streams and along beaches4 ,illustration3 uncaptioned ,if the pebbles embedded in the matrix are sharp and angular1 freshly broken and not worn1 the rock is called breccia and is generally found near the place where the fragments originated4 ,conglomerate or breccia may be made up of any type of rock or mineral1 most commonly durable material such as chert1 quartz1 quartzite1 granite1 and gneiss4 ,in ,illinois1 conglomerates commonly are found at the base of sandstone formations and as beds in the lower 8,coal ,measures40 ,they also are found in some gravel deposits4 ,,sandstone 7#h7 ,,sandstone is a clastic sedimentary rock consisting of sand-sized grains 7one sixty-fourth to one-sixteenth inch in diameter7 held together by a cementing material4 ,as sandstones become finer grained they grade into siltstones2 as they become coarser grained they grade into conglomerate4 ,the shape of sand grains in sandstones ranges from rounded to angular4 ,quartz is the dominant mineral in sandstone1 but other rock grains and mineral grains 7especially chalcedony1 feldspar1 muscovite1 hornblende1 magnetite1 or garnet7 generally are present4 ,sandstones are commonly cemented by carbonates1 silica1 iron oxides1 or clays4 ,most sandstones are a shade of gray or brown1 but the color may vary from gray or white to yellow1 brown1 or red4 ,the color probably depends on the type of cement1 the amount of organic material present1 and the amount and degree of oxidation of iron in the rock4 ,durability of sandstones depends largely on the character of the cement4 ,some sandstones crumble easily1 but others1 especially those cemented by iron oxides or silica1 are tough and durable4 ,sandstones break around the grains1 giving the broken surface a granular appearance4 ,sandstone crops out in many places throughout much of the state4 ,in ,la,salle and ,ogle ,counties1 large tonnages of sand are mined from the ,st4 ,peter ,sandstone and sold for a variety of uses1 including abrasive sand1 molding sand1 and sand for making glass4 ,in extreme southern ,illinois attractively colored sandstones have been quarried for building stone4 ,,quartzite 7#i7 ,,quartzite is a metamorphic rock that originally was quartz sandstone4 ,quartzites are produced by intense heat and_/or pressure1 probably aided by hot silica-bearing solutions4 ,the quartz grains may be so closely interlocked that individual grains are no longer recognizable4 ,the rock fractures conchoidally through both the grains and cement1 so the broken surface1 unlike that of sandstone1 is smooth and may even be glassy like quartz4 ,color depends upon the amount and kind of impurities present4 ,a quartzite that is all quartz is white or gray1 but iron or other elements may change the color to shades of purple1 yellow1 brown1 or red4 ,quartzite is a very resistant1 hard rock and cannot be scratched by a knife4 ,quartzite is abundant as boulders and pebbles in glacial drift of ,illinois1 having been brought into the state during the 8,ice ,age40 ,,shale 7#aj7 ,,shale is a common and important sedimentary rock composed of compacted clay or mud4 ,it is so fine grained that the minerals forming it generally cannot be identified without the aid of ,x-ray4 ,shales are composed mainly of clay minerals but1 like other sedimentary rocks1 generally include other minerals4 ,shales containing calcium carbonate are called calcareous shales4 ,most shales contain silt or sand particles2 if silt or sand is present in large quantity1 the rock is called silty shale or sandy shale4 ,if mica minerals are present in quantity in a shale it is called micaceous shale4 ,the particles of most clay minerals are thin and flat and overlap each other4 ,shales have a wide range of colors but most of those in ,illinois are gray4 ,a gray1 black1 or blue-gray color is caused by organic matter in the shale2 shades of red1 brown1 yellow1 or green are caused by iron compounds4 ,shale is widely distributed in ,illinois1 especially in 8,coal ,measures0 rocks1 and is used in manufacturing bricks1 drain tile1 building tile1 and lightweight aggregate4 ,,clay 7#aa7 ,,clay is an unconsolidated rock made up of a group of hydrous aluminum silicate minerals1 of which chlorite1 montmorillonite1 kaolinite1 and illite are the most abundant4 ,these minerals are formed by the weathering or alteration of other rocks and minerals4 ,clays are very fine grained and their minerals have tiny1 flat crystals that can be distinguished from each other only by laboratory methods4 ,although clays may appear to be similar1 their compositions vary greatly4 ,some clays are white1 but most are colored by iron compounds and organic matter4 ,wet clays have an earthy odor and generally are slick and plastic1 but dry clays are relatively hard and are greasy to the touch4 ,clays are abundant in ,illinois1 especially in soils1 in shales1 and as clay deposits4 ,in ,illinois the underclays that occur beneath coal beds are particularly well suited to the manufacture of bricks1 pottery1 stoneware1 and drain tile4 ,,limestone 7#ab7 ,,limestone is a sedimentary rock composed of particles of calcite 7calcium carbonate74 ,the crystals may range from fine to coarse4 ,many limestones contain other minerals1 such as chert1 clay1 or sand1 and in some places they grade into dolomite 7calcium magnesium carbonate74 ,many limestones are white or gray4 ,yellow or brown shades are caused by iron oxide impurities and dark gray to black colors by organic matter4 ,limestones form in various ways4 ,some are deposited when calcium carbonate precipitates from solution2 others are formed when the shells or skeletons of organisms such as brachiopods1 clams1 and corals accumulate on a sea floor4 ,if such fossils are very abundant1 the rock is called fossiliferous limestone4 ,limestone composed of tiny1 rounded concretions is called oolite or oolitic limestone4 ,limestone effervesces freely in dilute hydrochloric acid1 but dolomite must be powdered before it will effervesce4 ,in nature1 limestones may be dissolved by percolating water containing weak acid 7such as carbonic acid1 composed of water and carbon dioxide74 ,at many places in southern and southwestern ,illinois such solution of limestones has produced caves and caverns4 ,limestone outcrops are abundant in ,illinois1 especially along the bluffs of the ,mississippi1 ,ohio1 and ,illinois ,rivers4 ,limestone has many uses4 ,it is used for building stone1 road surfacing1 railroad ballast1 in the manufacture of portland cement1 and1 if of high purity1 for making lime and chemicals and as a flux in smelting metals4 ,it also is used1 as agricultural limestone1 to add calcium to the soil4 ,,peat 7#ac7 ,,peat is produced by the partial decomposition of plants that accumulate1 with varying amounts of mineral matter1 in old ponds1 swamps1 and lakes1 and in abandoned channels in valley bottoms along many rivers and streams4 ,peat may be an early stage in the formation of coal4 ,peat ranges from light to dark brown1 the color1 decomposition1 and compaction increasing with depth in the deposit4 ,some of the plant remains are clearly distinguishable and appear as fibrous fragments held together by the fine peat particles4 ,the type of peat common in ,illinois has a high water content4 ,before it is dried it is soft and spongy to the touch2 upon drying1 it loses much water and becomes harder4 ,peat is used as a fuel in some parts of the world1 but its heating value is low compared to that of coal4 ,it burns with a long flame and leaves a great deal of ash because of the silt and sand that were buried with the vegetation4 ,peat and peat moss are used chiefly as an absorbent1 as stable litter1 as insulating and packing material1 and by gardeners to increase the water-holding capacity of soils4 ,peat is found in many places in ,illinois but the largest deposits are in northeastern ,illinois4 ,,coal 7#ad7 ,,coal1 an organic stratified rock1 is formed from accumulated plant material and partially decayed plants that were buried during the 8,coal ,measures0 period in ,illinois more than #bjj million years ago4 ,sediments deposited over the peat-like organic material compacted it4 ,chemical changes gradually took place and resulted in the loss of water and gases1 leaving a higher percentage of carbon than the original material contained4 ,the amount of such change that has taken place determines the rank of the coal4 ,the lowest ranks are called lignite1 the intermediate group is called bituminous 7soft7 coal1 and coals of the highest rank1 with the highest carbon content1 are called anthracite 7hard coal74 ,mineral matter1 such as shale1 clay1 or pyrite1 generally is present in the coal and becomes ash when the coal is burned4 ,most coal mined in the ,united ,states is bituminous coal4 ,it is black1 brittle1 breaks into angular blocks1 has a shiny luster1 and generally shows a banded structure4 ,coal mining is an important industry in ,illinois1 and the state contains the largest known reserves of bituminous coal in the ,united ,states4 ,minable coal beds underlie about two-thirds of the state4 ,as many as #bj different coal beds have been mined in ,illinois1 the most important being the ,herrin 7,no4 #f7 and the ,springfield 7,no4 #e7 or ,harrisburg 7,no4 #e74 ,the coal in most mining areas averages #e to #g feet thick and in places attains a thickness of #ae feet4 ,in underground mines the coal is approached by vertical or inclined shafts4 ,in open cut1 or strip1 mines all of the overlying material 7overburden7 is removed1 leaving the coal exposed4 ,coal as much as #ajj feet deep is now being strip mined in ,illinois4 ,illinois coal is now used mainly for generating electric power1 for industrial purposes1 and for heating4 ,in industry1 coal is used extensively for power1 heating1 burning cement1 firing clay products such as brick1 tile1 pottery1 porcelain1 and china1 and making coke4 ,certain ,illinois coals when mixed with coal from the eastern part of the ,united ,states1 produce metallurgical coke for making steel4 ,gases1 oils1 and tars derived in processing coal for coke have been used for making many chemical products1 including dyes1 perfumes1 explosives1 medicines1 insecticides1 plastics1 and road tar4 ,,petroleum 7#ae7 ,,petroleum 7crude oil7 is classed as a mineral resource although it is a liquid hydrocarbon and not technically a mineral or rock4 ,it is1 however1 found in the pores and fractures of rocks4 ,the color of crude oil ranges from yellow through green and brown to black4 ,illustration3 uncaptioned ,arch 7anticline7 ,gas ,porous rock ,nonporous rock ,oil saturated rock ,water ,break 7fault7 ,nonporous rock ,oil saturated porous rock ,water saturated porous rock ,trap formed by change in character of rock ,water ,nonporous rock ,porous rock ,petroleum had its origin in the plants and animals buried in ancient sediments4 ,the organic matter changed slowly into the complex mixture of hydrogen and carbon compounds that is petroleum4 ,because gas is lighter than oil1 and oil in turn lighter than water1 gas and oil move upward in a porous rock containing all three4 ,gas moves to the highest position with oil next below and water in the lowest part of the rock4 ,oil pools exist where geologic barriers have stopped the movement of gas and oil4 ,arches 7upward folds or anticlines71 breaks 7faults71 and lateral changes from porous to nonporous rock are geologic features that serve to localize oil pools within the reservoir rock4 ,petroleum is obtained by drilling wells into the reservoir rock4 ,gas that is free or dissolved in the petroleum expands as pressure is released when the well is drilled and drives the oil to the well4 ,water in the reservoir rock also acts as a driving force4 ,when this natural pressure is no longer effective1 other methods 7secondary recovery7 are used to recover the oil remaining in the reservoir4 ,porous sandstones and limestones are the oil-bearing rocks4 ,illinois also has deposits of oil shale from which petroleum may be produced in the future4 ,thousands of products are derived from petroleum1 including gasoline1 kerosene1 naphtha1 lubricating oils and waxes1 medicinal oils1 salves1 heavy fuels1 road oils1 tar1 and asphalt4 ,,glaciated ,,pebbles 7#af7 ,,glaciated ,,pebbles are small stones whose shapes have been altered by the grinding action of a glacier4 ,such pebbles commonly have at least one flattened side that shows scratches 7called striae74 ,the striae were produced when the pebbles were pushed over bedrock or ground against other pieces of rock4 ,glaciers tore fragments from the bedrock over which they moved and the fragments accumulated in1 on1 and under the mass of ice4 ,the rock fragments were transported1 some of them far from their source1 and were deposited as the glacier moved along or when the ice melted4 ,soft rocks like limestone and dolomite are easily scratched1 but soft rocks cannot make grooves in hard igneous and metamorphic rocks4 ,therefore soft rocks have more striae4 ,glaciated pebbles can be found in deposits in many parts of the state1 especially in northeastern and east-central ,illinois4 ,however1 many deposits near the surface have been weathered and striae have been destroyed4 ,an especially good place to look for striated pebbles is in quarries and strip mines where glacial drift overburden has been removed4 ,pebbles found in such deposits show good striae for they are but little weathered4 ,,silica ,,sand 7#ag7 ,,silica ,,sand is the commercial name for sand composed almost entirely of grains of quartz4 ,sand of this kind is mined in ,illinois from the ,st4 ,peter ,sandstone in ,la,salle and ,ogle ,counties4 ,the coarser grains of the sand are characteristically rounded and frosted4 ,the frosting causes the sand to look white4 ,illinois silica sand has many uses4 ,it is used just as it is mined for molding sand in which metal castings are made1 for lining industrial furnaces1 and for many other purposes4 ,some of the sand is washed to remove the small amount of impurities present4 ,the washed sand is used for such purposes as making glass1 for grinding plate glass smooth1 for sand blasting1 for molding metal1 as fracturing sand to increase the production of oil wells4 ,some silica sand is ground to a fine powder and used as a fine abrasive1 as a filler in paint1 and as an ingredient in pottery1 glazes1 and enamel4 ,a specially prepared ,st4 ,peter sand1 known throughout the world as ,standard ,ottawa ,testing ,sand1 is used to test the strength of cements and as a laboratory standard in physical tests of other sands4 ,,molding ,,sand 7#ah7 ,,molding ,,sand is a mixture of sand and clay or other bonding material and is used to make molds in which metal is cast into various useful shapes4 ,there are two kinds of molding sands1 synthetic and natural bonded4 ,the first is an artificial mixture of silica sand and clay2 the second is a naturally occurring mixture of sand and a bonding material4 ,for casting1 molding sand is first moistened with water and shaped into a mold of the metal part to be reproduced4 ,the mold is then allowed to dry and the molten metal poured into it4 ,the bonding material in the sand must be strong enough to keep the mold in shape during these operations4 ,natural bonded molding sand is produced in ,fayette1 ,bond1 ,bureau1 ,carroll1 ,kankakee1 and ,rock ,island ,counties1 ,illinois4 ,,tripoli 7#ai7 ,,tripoli1 called amorphous silica in southern ,illinois1 is a white or light brown1 powdery substance that rubs off on the hands like chalk4 ,it consists mostly of very small particles of quartz that result from the weathering of calcareous chert or highly siliceous limestone4 ,it is finely ground and used as 8white rouge0 for polishing optical lenses1 as a filler in paints1 in making ceramic products1 as a component of buffing compounds1 and as a fine abrasive4 ,tripoli occurs in ,alexander and ,union ,counties and is milled at ,elco and ,tamms in ,alexander ,county4 ,,fuller',s ,,earth 7#bj7 ,,fuller',s ,,earth is clay or silty clay material that contains very fine silica4 ,it is soft1 nonplastic1 opaque1 has a greasy feel when wet1 and does not readily break up in water4 ,its color varies from blue-gray to yellow or buff4 ,fuller's earth is valuable for its unique property of absorbing and decolorizing substances4 ,the material was first used to 8full0 or remove grease from woolen cloth1 hence its name4 ,it also has been used to filter and bleach mineral and vegetable oils by absorbing dark organic matter4 ,in ,pulaski ,county in extreme southern ,illinois the ,porter's ,creek ,formation contains deposits of clay that were at one time the source of fuller's earth and still afford clay whose absorbent properties make it useful as litter and as sweeping and cleaning compound4 ,,quartz 7#ba7 ,,quartz is the most common of all minerals1 making up about #ab percent of the earth's crust4 ,there are two main types of quartz--crystalline quartz and dense1 crypto-crystalline 7submicroscopic7 quartz4 ,many dense varieties occur in ,illinois1 probably the most common are chert or flint4 ,illustration3 uncaptioned ,crystals of quartz are typically six-sided1 elongated1 have sharply pointed pyramid-like ends1 and are apt to grow together forming twins4 ,good crystals are rare in ,illinois1 and the crystal structure is not apparent in the commonly occurring grains and masses4 ,quartz is brittle and hard4 ,it may be colorless or tinted1 transparent or translucent1 but more commonly it is white and nearly opaque4 ,transparent quartz looks much like ordinary glass1 but it scratches glass easily4 ,it has a glassy to brilliant luster and breaks irregularly or with a good conchoidal fracture4 ,some varieties of quartz that are used for semiprecious gems are chalcedony1 agate1 onyx1 and jasper4 ,chalcedony is waxy1 smooth1 generally translucent1 white to gray1 blue1 brown1 or black4 ,agate is a form of chalcedony that has a mottled or variegated banded appearance and may be yellow1 green1 red1 brown1 blue1 gray1 or black4 ,onyx is agate with parallel bands that as a rule are brown and white or black and white4 ,jasper1 an impure opaque quartz1 generally is red4 ,quartz occurs as rock crystal 7colorless1 transparent71 milky quartz 7white1 nearly opaque71 and smoky quartz 7smoky yellow to gray or brown7 in geodes from the ,warsaw and ,keokuk ,limestones of the ,nauvoo-,hamilton-,warsaw area and as vein and cavity fillings associated locally with fluorite1 sphalerite1 and galena in extreme southern ,illinois4 ,it also occurs as vug 7cavity7 fillings in limestones and sandstones4 ,,feldspar 7#bb7 ,,feldspar is the name applied to a group of minerals that are the second most common of all the earth's minerals4 ,all feldspars are composed of aluminum1 silicon1 and oxygen1 combined with varying amounts of one or more metals1 particularly potassium1 sodium1 calcium1 and lithium4 ,the minerals are hard1 have a smooth glassy or pearly luster1 and cleave along two planes nearly at right angles to each other4 ,feldspars are fairly light weight4 ,the streak is white1 but the color of the mineral is highly variable1 although potassium and sodium-bearing feldspar are commonly white or pink and most plagioclase feldspar is gray4 ,feldspars are essential parts of the crystalline igneous rocks4 ,their decomposition products are present in most soils4 ,in ,illinois relatively small feldspar crystals can be found associated with quartz and other minerals in granite and gneiss boulders and pebbles in glacial drift4 ,,mica 7#bc7 ,,mica is the name of a family of complex aluminum silicate minerals that can be split easily into paper-thin1 flexible sheets4 ,if broken across the grain at right angles to the flat1 smooth surface they fracture raggedly4 ,in a single mica crystal the sheets range from more or less transparent to translucent and are arranged one on top of another like a deck of cards4 ,micas are tough and somewhat elastic1 soft enough to be split and scratched by a fingernail1 and are light weight4 ,they have a nonmetallic1 glassy or pearly luster1 although yellow mica may appear to be metallic4 ,color and streak depend upon the chemical composition of the mineral4 ,muscovite1 or white mica1 contains potassium and makes a colorless or white streak4 ,biotite1 or black mica1 contains iron and magnesium and is commonly dark green or black1 although it may be shades of yellow or brown2 its streak is uncolored4 ,mica is abundant as tiny1 shimmering flakes in ,illinois sands1 sandstones1 and shales 7which are then said to be micaceous74 ,it also is common in many varieties of igneous and metamorphic rocks4 ,white or yellow flakes may show a brilliant luster and may be mistaken for silver1 platinum1 or gold1 but those minerals are heavy and malleable whereas mica is not4 ,,calcite 7#bd7 ,,calcite1 a common rock-forming mineral1 consists of calcium carbonate4 ,the mineral is white or colorless1 but impurities may tint it shades of yellow or gray4 ,transparent calcite is more rare than the tinted varieties4 ,transparent calcite possesses the property of double refraction2 an image appears double when viewed through a calcite cleavage block4 ,calcite has a glassy luster1 its streak is white or colorless4 ,the mineral is of medium hardness and can be scratched by a penny or a piece of window glass but not by the fingernail4 ,it is fairly light weight and effervesces freely in cold dilute hydrochloric acid4 ,illustration3 uncaptioned ,calcite has a variety of crystal forms but in ,illinois flattened block-shaped crystals and elongate crystals with tapering points 78dogtooth spar07 are the most common4 ,when broken1 calcite cleaves into six-sided blocks called rhombs4 ,crystals of calcite are found in ,illinois as linings in geodes in certain limestones and shales1 especially in the ,nauvoo-,hamilton-,warsaw area1 and as crystalline masses in limestone and dolomite4 ,small amounts of clear crystalline calcite are associated with various ores in northwestern and extreme southern ,illinois4 ,calcite is the principal mineral in limestones and occurs as a component of many concretions4 ,,fluorite 7#be7 ,,fluorite1 or fluorspar1 is made up of the elements calcium and fluorine4 ,the mineral is easily identified by its perfect cleavage1 color1 and hardness4 ,it occurs in cubic crystals that may be twinned but is more often found as irregular masses4 ,it can be split into diamond-shaped1 eight-sided forms 7octahedrons74 ,fluorite is commonly gray1 white1 or colorless1 but it may be green1 blue1 purple1 pink1 or yellow4 ,the streak is colorless and the luster glassy4 ,it can be scratched by a knife or a piece of window glass1 is fairly light weight1 and is transparent to translucent4 ,extensive deposits of fluorite1 one of ,illinois' important commercial minerals1 occur in ,hardin and ,pope ,counties in extreme southern ,illinois1 where it is associated with galena1 sphalerite1 calcite1 barite1 and other less abundant minerals4 ,fluorite is used to make hydrofluoric acid1 to form a fluid slag in the production of iron and steel1 in the manufacture of aluminum1 to make many chemical products1 and in the ceramic industry1 in which it is used to make colored glass1 enamels1 and glazes4 ,,gypsum 7#bf7 ,,gypsum1 hydrous calcium sulfate1 is a colorless1 transparent to translucent mineral when pure1 but it often is stained yellow by impurities4 ,it has a white streak1 is soft enough to be scratched by a fingernail1 and is light weight4 ,illustration3 uncaptioned ,gypsum occurs in several forms4 ,selenite is a coarsely crystalline1 transparent variety1 composed of flat1 nearly diamond-shaped crystals that can be split easily into thin sheets1 have a glassy luster1 and often grow together to form 8fishtail twins40 ,crystals of selenite occur in shales of the 8,coal ,measures0 of southern1 north-central1 and western ,illinois1 and can be picked up at the surface4 ,satin spar has crystals like silky threads closely packed together1 splits parallel to the fibers1 and is found as fillings in rock cracks and as thin layers in shales4 ,massive gypsum is granular4 ,gypsum deposits occur deep underground in ,illinois but thus far have not been mined4 ,,chert 7#bg7 ,,chert1 one of the main forms of silicon dioxide1 is cryptocrystalline 7submicroscopic7 quartz4 ,most of the chert in ,illinois is white or gray1 but impurities stain many deposits yellow1 brown1 or even pink4 ,chert is so hard that it can scratch glass and ordinary steel4 ,it is fairly light weight1 dense1 opaque1 and brittle2 the luster is dull4 ,flint1 a variety of chert1 is generally dark colored1 more dense1 may have a glassy luster and be transparent in thin flakes4 ,both chert and flint have a smooth1 curved 7conchoidal7 fracture1 but flint tends to break with thinner1 sharper edges4 ,indians used flint and chert to make arrow points and spearheads4 ,chert occurs as rounded masses 7nodules and concretions7 or as irregular layers in limestones and dolomites in northern1 western1 southwestern1 and southern ,illinois4 ,because chert is hard and more resistant to weathering than limestone or dolomite1 it often remains after the rest of the rock has weathered away4 ,chert also is abundant in many glacial deposits because it is hard and resists solution4 ,streams that flow through cherty bedrock or glacial deposits carry pebbles along and concentrate them as gravel in stream channels4 ,cherty stream gravels are especially abundant in western and southern ,illinois4 ,brown chert gravels in the southern part of the state are used for road gravel4 ,other deposits in extreme southern ,illinois1 consisting of angular fragments of chert and a small amount of clay 7known locally as novaculite gravel7 also are used for road surfacing4 ,white and gray chert occur as massive bedrock deposits several hundred feet thick in ,union and ,alexander ,counties4 ,,pyrite ,,and ,,marcasite 7#bh7 ,,pyrite and ,,marcasite are iron disulfide compounds4 ,they look much alike but have different crystal forms4 ,both are brittle1 hard1 brassy yellow with metallic luster1 and opaque4 ,the best distinguishing feature is crystal shape4 ,the pyrite crystals are cubes1 but the marcasite crystals are blade- or needle-shaped4 ,pyrite and marcasite have been mistaken for gold because they are yellow and metallic and hence are sometimes referred to as 8fool's gold04 ,they1 however1 are harder than gold1 tarnish1 and leave a dark streak1 whereas gold is soft1 very heavy1 does not tarnish1 and leaves a yellow streak4 ,gold is malleable1 but pyrite or marcasite are reduced to powder if they are pounded and give off a noticeable odor of sulfur dioxide gas if they are heated4 ,pyrite and marcasite are found in many deposits in ,illinois4 ,they occur as grains or larger masses in some clays1 shales1 and limestones4 ,they also occur with the lead and zinc ores of northwestern ,illinois and1 in small amounts1 with the fluorite and associated minerals in the extreme southern part of the state4 ,both pyrite and marcasite are common as surface coatings1 veins1 and concretionary structures in coal and in dark shales associated with coal4 ,they are referred to as 8coal brasses0 or 8sulfur0 when found as impurities in coal4 ,a potential use for pyrite and marcasite is in the manufacture of sulfuric acid for industrial use4 ,coal brasses recovered from ,illinois coal have been so used4 ,,limonite 7#bi7 ,,limonite is an iron oxide containing water and has a complex chemical composition4 ,the limonite found in ,illinois may be yellow1 orange1 red1 brown1 or black1 but its streak is always yellowish brown4 ,the mineral may have a glassy or an earthy luster4 ,it may be too hard to be scratched by a knife4 ,it is of medium weight4 ,limonite is common and occurs as concretions and cavity fillings in sedimentary rocks1 and as coatings on them1 especially sandstone4 ,it also occurs as iron rust1 as scum on stagnant water1 and it accumulates around rootlets in soils4 ,small amounts color limestone1 dolomite1 clay1 shale1 sandstone1 and gravel4 ,some sands are firmly cemented by brown or black limonite and look much like iron ore4 ,clays containing a high percentage of limonite are called ocher4 ,in some states limonite is mined as an iron ore1 and in ,illinois it was so used in ,hardin ,county in the middle #ahjj's1 but deposits are not large enough for profitable use now4 ,,sphalerite 7#cj7 ,,sphalerite1 zinc sulfide1 is a major ore of zinc4 ,it has a resinous luster and a white1 yellow1 or brown streak4 ,illinois sphalerite is generally yellow1 yellowish brown1 reddish brown1 or brownish black4 ,it is of medium weight1 brittle1 can be scratched by a piece of window glass but not by a penny4 ,it is commonly opaque but may be translucent on thin edges4 ,sphalerite is mined with galena in northwestern ,illinois and in extreme southern ,illinois with galena and fluorite4 ,small crystals occasionally are found in limestones and as crystalline masses in clay-ironstone concretions4 ,,galena 7#ca7 ,,galena1 lead sulfide1 is the principal ore of lead4 ,it is steel gray1 heavy1 opaque1 and has a bright metallic luster1 though the shiny surface may be dulled by a coating of lead carbonate4 ,it has a gray or black streak1 is soft enough to mark paper1 and can be scratched by a penny4 ,the cube-shaped crystals readily break into cubic1 right-angled fragments4 ,probably the most obvious features of the mineral are its bright metallic luster on fresh surfaces1 high specific gravity1 and cubic cleavage4 ,illustration3 uncaptioned ,at many places galena is argentiferous 7silver-bearing71 but ,illinois galena is relatively unimportant for its silver content4 ,as a source of lead1 however1 it is an important commercial product of the state4 ,scattered pieces of galena are found at many places in ,illinois4 ,some occur in the glacial deposits1 others occur as small pockets and as crystals in limestones and geodes4 ,in only two areas of the state are deposits of commercial value4 ,in northwestern ,illinois galena occurs in association with sphalerite2 in extreme southern ,illinois it occurs in association with fluorite and sphalerite4 ,,concretions 7#cb7 ,,concretions are concentrations of inorganic sedimentary material within other sediments4 ,minerals that commonly form concretions are silica 7in the form of opal1 chert1 chalcedony1 and quartz71 calcite1 siderite1 pyrite1 marcasite1 and limonite4 ,concretions may form either as the sediment around them is forming or after the sediment around them has hardened4 ,they may be formed when water containing dissolved minerals seeps through the sediment or rock and leaves a concentration of mineral matter in a cavity or around a central particle 7nucleus7 such as the remains of a plant or animal4 ,portions of rock may also become firmly cemented by such mineral matter4 ,concretions range in size from minute particles to objects several feet in diameter4 ,shapes range from spheres to tubes4 ,many are globular or lumpy-surfaced1 some are smooth4 ,because concretions generally are harder than the surrounding rock in which they have formed1 they do not weather away as readily and may remain after the surrounding material has been eroded4 ,concentrations of calcite are found in loess deposits4 ,they may look like bizarre1 knobby figurines1 and the ,germans called them loess kindchen 7little children of the loess74 ,ironstone concretions1 especially common in many ,illinois shales1 are formed by a local concentration of the mineral siderite 7iron carbonate7 in the rock4 ,the concretions found in weathered outcrops commonly are partly or entirely weathered to limonite4 ,some ironstone concretions grow together into odd shapes4 ,mazon ,creek ironstone concretions of northeastern ,illinois1 world famous for their fossils1 are sideritic4 ,the concretions are commonly covered with limonite1 the result of oxidation4 ,limonite concretions1 generally with a high content of clay1 silt1 or sand1 occur in loess1 shale1 and sandstone4 ,concretions of chert and other forms of silica are common in limestones4 ,in many places1 because of their greater resistance to weathering1 lenses and nodules of chert protrude from the beds4 ,pyrite or marcasite occur as concretions or concretion-like masses in some coal beds and in the black shales1 sometimes popularly called 8slates10 above coal beds4 ,some other ,pennsylvanian clays and shales also contain concretions or coarsely crystalline aggregates of these minerals4 ,,geodes 7#cc7 ,,geodes are roughly spherical bodies that may be filled with layers of minerals1 lined with crystals1 or both4 ,the outer layer of geodes found in ,illinois as a rule is composed of chalcedony1 a form of finely crystalline silica4 ,geodes differ from concretions in that they form inward from the outer shell1 whereas concretions develop outward from a center4 ,even if geodes have been completely filled by mineral matter1 their inward-projecting crystals prove that they formed within a cavity4 ,in a partly filled cavity1 crystals generally are well formed because they grew without being crowded4 ,some of the best mineral specimens known in ,illinois are found as crystal linings in geodes4 ,illustration3 uncaptioned ,quartz is the most common mineral deposited in geodes1 but calcite1 aragonite1 dolomite1 siderite1 pyrite1 galena1 fluorite1 and sphalerite also are found4 ,geodes ranging in size from less than one inch to a foot or more in diameter can be gathered from streams where they have accumulated as residual boulders after the rock in which they were enclosed has been eroded4 ,hollow geodes are the most desirable because they have better crystals4 ,they can be distinguished from solid ones by their comparative lightness of weight4 ,geodes are commonly associated with limestone and dolomite1 at some places with shale4 ,in ,illinois they can be found most easily in the ,warsaw ,formation in the area of ,nauvoo1 ,hamilton1 and ,warsaw1 but they also occur in other areas and other formations4 ,,animal ,,fossils 7#cd7 ,prehistoric animals lived in water1 on land1 and in the air1 and left both direct and indirect evidence of their existence1 evidence we now call fossils4 ,millions of ancient animals died without leaving a trace1 but some1 especially those that had hard parts such as shells1 bones1 or teeth1 may be found preserved in rocks much as they were when buried beneath sediment on the floor of an ancient sea4 ,sometimes only imprints of the outside or fillings of the inside of the shells remain1 the original material having been completely dissolved4 ,footprints of land or amphibious animals1 burrows made by clams1 or holes made by worms also are fossils4 ,illustration3 uncaptioned ,the animals whose remains are fossilized lived and died while the sediments that contained them were being deposited1 and they provide clues to the types of life and climate then existing4 ,fossils of animals characteristic of a certain time are an index to the age of formations where they occur4 ,for example1 if a certain trilobite 7an ancient relative of the crayfish and lobster7 is known to have lived only during a definite time1 then all rocks in which it is found are the same age4 ,fossils of animals that lived in the sea are exposed in rocks in many parts of ,illinois1 especially in quarries1 river bluffs1 and road cuts4 ,the oldest fossils found in ,illinois are shells of marine animals--snails1 corals1 crinoids1 brachiopods1 trilobites1 pelecypods 7clams71 cephalopods1 bryozoa1 arthropods1 and others4 ,the youngest fossils are teeth and bones of prehistoric bison1 giant beavers1 deer1 mammoths and mastodons of the 8,ice ,age10 and snails found in glacial loess4 ,,plant ,,fossils 7#ce7 ,,plant ,,fossils are the remains of prehistoric plants4 ,woody structures of plants aid preservation just as hard parts of animals do4 ,leaves and plants without much woody material generally were well preserved only if they were buried quickly in fine1 soft sediment4 ,the most famous ,illinois plant fossils are those from the ,mazon ,creek area in ,grundy and ,will ,counties of northeastern ,illinois4 ,the plant material acted as a nucleus around which iron minerals accumulated to form concretions4 ,many good fossils--of trunks1 branches1 leaves1 and seeds--are found in coals and in shale directly overlying coals4 ,descendants of 8,coal ,measures0 plants1 such as ferns1 mosses1 and rushes1 are still living today1 but they no longer thrive as they did in the warm1 moist climate of the ,pennsylvanian forests4 ,some plants of ,pennsylvanian age are petrified1 and occasionally such trees or stumps are found4 ,petrified trees are found also in the upper ,mesozoic deposits of southern ,illinois4 ,fossils of 8,ice ,age0 plants closely related to forms living at the present time are occasionally found in peat bogs or scattered throughout glacial deposits4 ,illustration3 uncaptioned ,,keys ,,for ,,identification ,,of ,,common ,,illinois ,,rocks ,,and ,,minerals ,two keys1 one for minerals and one for rocks1 briefly present clues that may aid the collector in identifying rocks and minerals found in ,illinois4 ,in outline form1 the keys are a guide to some of the easily observable properties that various rocks and minerals display4 ,the rocks and minerals in the school set of 8,typical ,rocks and ,minerals of ,illinois0 are included1 plus other relatively common ones you might find in ,illinois4 ,because of the great diversity of rocks and minerals in this state1 the keys are not conclusive4 ,it is therefore suggested you consult other more complete keys 7such as that in ,dana's ,manual of ,mineralogy7 when identifying rocks and minerals that are either from other states or are difficult to identify4 ,the minerals 7p4 #cj-ce7 are arranged in two groups3 #a7 those with a metallic luster1 and #b7 those with a nonmetallic luster4 ,each group is arranged according to increasing hardness4 ,other characteristics such as color1 streak1 cleavage1 fracture1 and composition are listed4 ,the rocks 7p4 #cf-ci7 are arranged according to their reaction to dilute hydrochloric acid applied to a scratched surface4 7,the acid reacts more readily to powdered material produced by scratching the rock47 ,after the reaction to acid has been determined1 the texture and components of the rock should be noted4 ,because rocks grade into one another1 clear distinctions are not always possible4 ,,mineral ,,identification ,,key ,i4 ,,metallic ,,luster1 ,,streak ,,colored ,c--color ,h--hardness ,remarks ,name and ,s--streak ,cl--cleavage composition ,f--fracture ,a4 ,hardness not more than #b4e ,c--lead gray ,h--#b4e ,very heavy2 occurs as ,galena 7#ca7 ,s--black ,cl--cubic2 crystals1 grains1 or ,pb,s perfect in #c masses2 easily directions identified by color and ,f--subconchoidal cleavage or even ,c--copper red ,h--#b4e ,very heavy2 apt to have ,native copper ,s--metallic1 ,cl--none green coating2 distorted ,cu shiny ,f--jagged or wirelike forms2 malleable ,b4 ,hardness greater than #b4e but not greater than #f4e ,c--yellow-brown ,h--#e4e 7may be as ,in earthy masses2 ,limonite 7#bi7 to black low as #a7 coloring material in ,fe,o7,,oh7,h,o ,s--yellow-brown ,cl--none many sandstones1 ,f--uneven conglomerates1 and soils2 often mixed with and difficult to distinguish from goethite and other iron minerals ,c--brassy yellow ,h--#f ,as compact masses1 ,pyrite 7#bh7 ,s--greenish black ,cl--poor grains1 cubes1 and in #h- ,fe,s ,f--conchoidal to and #ab-sided crystals2 uneven commonly associated with coal1 and with lead-zinc ores of northwestern ,illinois ,c--pale brassy ,h--#f ,as fibrous1 radiating1 ,marcasite yellow to ,cl--poor tabular1 and cocks-comb ,fe,s 7#bh7 silver white ,f--uneven crystals or compact ,s--greenish gray masses2 usually lighter colored than pyrite1 but difficult to distinguish from pyrite2 associated with coal1 and with lead-zinc ores of northwestern ,illinois ,,ii4 ,,nonmetallic ,,luster1 ,,streak ,,white ,a4 ,hardness not greater than #b 7can be scratched by fingernail7 ,c--usually white ,h--#b ,commonly found in ,gypsum 7#bf7 but may be ,cl--perfect in ,illinois as twinned or ,ca,s,o#b;,h,o almost any color one direction1 needle-shaped crystals less perfect in in weathered shales two others containing pyrite and calcium carbonate ,c--white or a ,h--#b ,as needle-shaped ,melanterite shade of green crystals or powdery ,fe,s,o#g;,h,o coating on pyrite or marcasite2 has an astringent taste ,b4 ,hardness greater than #b but not greater than #c 7,can be scratched by a penny7 ,c--colorless1 ,h--#b-b4e ,in scales or 8books02 in ,muscovite silver white1 ,cl--perfect in splits into thin sheets2 7white mica7 gray1 brown one direction common in sandstones1 7#bc7 shales1 and in igneous 7,,oh7,k,al and metamorphic rocks ,al,si,o ,c--brown or black ,h--#b4e-c ,as scales or 8books02 ,biotite 7#bc7 ,cl--perfect in splits into thin sheets2 7black mica7 one direction common in igneous and 7,,oh7,k7,mg1,fe7 metamorphic rocks but ,al,si,o not in sedimentary rocks such as sandstone or shale ,c--colorless1 ,h--#c ,common mineral2 ,calcite 7#bd7 white1 gray1 ,cl--perfect in effervesces vigorously ,ca,c,o and various three in cold acid2 occurs in tints directions1 not many crystal forms and at right angles as fibrous1 banded1 and 7rhombohedral7 compact masses2 chief mineral in limestones ,c--white1 gray1 ,h--#c ,very heavy2 commonly in ,barite red1 or almost ,cl--perfect in tabular crystals united ,ba,s,o any color one direction1 in diverging groups1 as less perfect in laminated or granular two other masses2 associated with directions fluorite in southern ,illinois ,c4 ,hardness greater than #c but not greater than #e 7,cannot be scratched by penny2 can be scratched by knife7 ,c--white1 gray1 ,h--#c4e ,relatively heavy2 ,witherite light yellow ,cl--in one effervesces in acid2 ,ba,c,o direction associated with fluorite ,f--uneven and barite in southern ,illinois but is not abundant ,c--white1 pink1 ,h--#c4e ,in grains1 rhombohedral ,dolomite gray1 or light ,cl--perfect in crystals and cleavable ,ca,mg7,,co7 brown three or granular masses2 directions1 not effervesces slowly in at right angles cold acid when powdered1 7rhombohedral7 more vigorously in warm acid2 principal mineral in rock called dolomite ,c--colorless1 ,h--#c4e ,in fibrous or compact ,cerussite white1 gray1 masses or may be in ,pb,c,o grayish black orthorhombic crystals as a coating on galena2 very heavy2 effervesces in acid2 formed by alteration of galena ,c--brown to gray ,h--#c4e ,in fibrous or botryoidal ,siderite ,s--usually white ,cl--in three masses or rhombohedral ,fe,c,o but may tend directions not crystals2 effervesces in toward brown at right angles hot acid when weathered 7rhombohedral7 slightly curved surfaces ,c--yellow1 ,h--#c4e ,in crystals1 in fibrous ,sphalerite yellow-brown to ,cl--parallel to or layered masses2 ,zn,s 7#cj7 almost black dodecahedral associated with galena ,s--light yellow faces2 in six in northwestern to brown directions ,illinois1 with fluorite and galena in southern ,illinois ,c--colorless1 ,h--#d ,in cubes and cleavable ,fluorite 7#be7 white1 yellow1 ,cl--perfect1 masses2 many colors2 7,fluorspar7 purple1 green1 parallel to mined in ,hardin and ,pope ,ca,f blue octahedral counties faces2 in four directions ,c--white1 tinted ,h--#e ,as crystalline ,smithsonite yellow1 blue1 incrustations or in ,zn,c,o or green earthy or compact masses2 associated with fluorite-sphalerite ores in southern ,illinois1 with galena and sphalerite in northwestern ,illinois ,d4 ,hardness greater than #e but not greater than #g ,c--white1 green1 ,h--#e-f ,in long1 slender #f-sided ,amphibole ,group brown1 black ,cl--in two crystals2 cleavage angle 7,mg1,fe1,ca7 directions important in 7,si,o77,,oh7 intersecting at differentiating from 7may also about #fj and pyroxenes2 common in contain ,na or #abj metamorphic and some ,al7 igneous rocks ,c--gray1 dark ,h--#e-f ,crystals short1 stout1 ,pyroxene ,group green1 black1 ,cl--in two and #h-sided2 cleavage 7,mg1,ca1,fe7 dark brown1 directions angle important in 7,si,o7 bronze intersecting at differentiating from about #ij amphiboles2 common in igneous and some metamorphic rocks ,c--white1 gray1 ,h--#f ,as crystals1 cleavable ,feldspar ,group pink1 light ,cl--in two masses and grains2 7#bb7 blue1 green directions common in igneous and ,k1 ,na1 ,ca1 ,ba nearly at right metamorphic rocks1 also 7,al1 ,si7,o angles in stream gravel and sand2 many varieties ,c--white when ,h--#g ,finely crystalline ,chalcedony pure2 may be ,cl--none variety of quartz2 ,si,o colored by ,f--conchoidal botryoidal or impurities concretionary masses2 lining in geodes ,c--colorless1 ,h--#g ,most abundant mineral2 ,quartz 7#ba7 white1 or ,f--conchoidal occurs in #f-sided ,si,o almost any color crystals capped by pyramids1 in grains or masses2 principal mineral in sandstone1 also abundant in igneous and metamorphic rocks2 is a variety of silica ,c--red ,h--#g ,a variety of quartz ,jasper ,f--conchoidal usually colored red by ,si,o hematite inclusions2 common in glacial and river sand and gravel found along ,lake ,michigan shores and in the ,mississippi ,river ,c--many2 ,h--#g ,cloudy banded variety of ,agate arranged in ,f--conchoidal silica2 widely used as ,si,o bands semi-precious stones4 ,onyx and silicified wood are forms of agate2 found in glacial gravels and upper ,mesozoic sediments in southern ,illinois ,e4 ,hardness greater than #g 7cannot be scratched by quartz7 ,c--red1 brown1 ,h--#g4e ,irregular grains or ,garnet ,group yellow1 green1 ,cl--poor masses2 sometimes as 7,ca1,mn1,fe1,mg7 black1 white ,f--even #ab-1 #bd-1 and #cf-sided 7,al1,cr77,si,o7 crystals2 abundant in glacial sands and ,lake ,michigan beach sands2 common in metamorphic rocks ,,rock ,,identification ,,key ,,sample ,scratch with a knife and apply dilute acid 7,h,cl7 ,if rock does not scratch1 go directly to ,i1 ,,ii1 or ,,iii ,no effervescence or very slight effervescence ,i ,coarse-grained 7p4 #cg7 ,,ii ,fine-grained 7p4 #ch7 ,,iii ,organic 7p4 #ci7 ,slight effervescence gray1 light gray1 white1 or brown3 ,dolomite ,vigorous effervescence ,composed of pebbles that effervesce ,rounded pebbles3 ,limestone conglomerate ,angular pebbles3 ,limestone breccia ,composed of crystals of calcite1 fossil shells1 or oolites3 ,limestone ,composed of banded layers of crystalline calcite2 commonly found in caves1 forming stalactites and stalagmites3 ,travertine ,large amount of insoluble residue left on acid-treated surface ,individual grains seen with unaided eye3 ,calcareous sandstone ,individual grains not seen with unaided eye3 ,calcareous shale ,composed of porous or cellular mass of calcite2 commonly found near springs and waterfalls3 ,tufa ,i ,,coarse-,,grained ,,rocks ,a4 ,rock consists of interlocking grains or crystals1 easily seen2 too hard to scratch with a knife #a4 ,crystals aligned in one direction a7 ,crystals in parallel bands with layers of quartz and feldspar separated by mica and other minerals ,gneiss 7#f7 b7 ,crystals in thin parallel bands2 tends to split into thin sheets parallel to banding2 some varieties may be scratched with a knife ,schist 7#f7 #b4 ,crystals not aligned in any particular direction a7 ,light gray1 pink1 red1 or tan with only a few dark minerals2 feldspar and quartz principal minerals ,granite 7#a7 b7 ,dark to medium gray2 composed of feldspar and dark minerals with little quartz ,gabbro 7#b7 c7 ,dark green to black2 essentially dark minerals1 may have some feldspar2 quartz generally lacking ,peridotite 7#e7 d7 ,light color2 similar to granite in texture but lacks quartz2 composed of feldspar and some dark minerals ,syenite e7 ,large1 easily seen crystals set in a fine- to extremely fine-grained background2 any color ,porphyry 7#c7 f7 ,essentially quartz2 grains may be identifiable2 specimens break through rather than around grains ,quartzite 7#i7 ,b4 ,rock composed of individual rock particles or fragments1 non-interlocking crystals1 cemented or not cemented together2 may or may not be scratched with a knife #a4 ,particles or fragments not uniform in size2 a mixture of pebbles1 sand1 and smaller materials a7 ,solid rock consisting of particles or fragments generally rounded and cemented together ,conglomerate 7#g7 b7 ,solid rock consisting of particles or fragments1 generally angular and cemented together ,breccia c7 ,fragments ranging in size from clay to large boulders2 may be compacted1 but not cemented2 much clay generally present2 may effervesce ,glacial till d7 ,loose particles of many sizes1 not cemented together2 some particles may effervesce ,gravel #b4 ,rock particles or fragments1 about the size of grains of sugar 7#b to 4#je mm7 a7 ,loose particles consisting largely of quartz ,sand b7 ,solid rock consisting largely of quartz2 can be separated easily into individual particles2 granular2 breaks around rather than through grains ,sandstone 7#h7 ,,ii ,,fine-,,grained ,,rocks ,a4 ,cannot be scratched easily with a knife2 crystals or particles not easily seen with the unaided eye2 very hard1 difficult to break2 may contain a few crystals or particles large enough to see2 granular #a7 ,dense2 brittle2 splintery or conchoidal fracture2 sharp edges and corners when broken2 often associated with limestone2 usually white or gray2 very dense1 dull varieties called flint ,chert 7#bg7 #b7 ,light gray1 pink1 red1 or tan varieties common2 boulders or fragments in the glacial drift ,felsite #c7 ,dark gray1 greenish1 black1 or maroon varieties common2 may have small mineral-filled cavities2 occurs as boulders or fragments in the glacial drift ,basalt 7#d7 #d7 ,essentially quartz2 grains may be identifiable2 specimens break through rather than around grains ,quartzite 7#i7 ,b4 ,may or may not be scratched with a knife2 fairly uniformly fine grained #a7 ,soft2 feels slippery or soapy when wet2 may disintegrate in water2 gives off an earthy odor when breathed upon ,clay #b7 ,loose2 gritty2 particles smaller than table salt ,silt #c7 ,solid rock2 often in thin beds or sheets2 separates into silt2 mica flakes may be present2 may contain fossils2 may effervesce slightly ,siltstone #d7 ,solid rock2 breaks into thin platy sheets2 may feel slippery when wet2 black to gray2 may contain fossils2 shows thin laminations2 may effervesce ,shale 7#aj7 #e7 ,solid rock3 does not break into thin platy fragments2 may effervesce slightly ,mudstone #f7 ,solid rock2 usually gray or black2 splits into platy sheets or slabs2 harder than shale ,slate #g7 ,powdery2 white or light brown2 commonly associated with chert and quartz from which it forms ,tripoli 7#ai7 ,,iii ,,organic ,,rocks 7,,dark ,,colored7 ,a4 ,soft2 spongy when wet2 very lightweight when dry2 forms in swampy places #a7 ,fine mass with coarse plant fragments2 dark gray to black ,peat 7#ac7 #b7 ,plant fragments small and not easily recognized2 fine-grained2 black to dark gray2 earthy ,muck ,b4 ,hard but can be scratched with a knife #a7 ,black2 contains bands of shiny and dull material2 burns well ,coal 7#ad7 #b7 ,dark gray to black2 does not contain shiny bands2 splits into thin sheets2 burns poorly or not at all ,bituminous shale ,,equipment ,,for ,,collecting #a4 ,hammer 7bricklayer's7 with one chisel or pick head4 #b4 ,cold chisel about #f inches long with an edge about -inch wide4 #c4 ,dilute hydrochloric 7muriatic7 acid 7#aj percent solution7 in a dropper bottle for testing the presence of carbonate minerals4 ,mark the bottle ,,poison4 ,if acid is spilled on skin or clothing1 wipe immediately and1 if possible1 rinse with water4 #d4 ,magnifying glass or hand lens--#aj power is probably most useful4 #e4 ,hardness testers--penny1 square of window glass1 pocket knife1 or nail4 #f4 ,streak plate--piece of unglazed white porcelain 7such as the back of a tile7 for testing the color of the streak of minerals4 #g4 ,notebook and pencil for keeping records of the locality and bed from which specimens are collected4 #h4 ,collecting bag--a musette bag1 a knapsack1 or similar bag of strong material4 #i4 ,heavy gloves and goggles to protect hands and eyes4 #aj4 ,labels and wrappings4 ,field identification of specimens may be written on adhesive tape and attached to the specimen or on a slip of paper enclosed in the wrapping4 ,newspaper1 brown paper1 or paper bags can be used for wrapping specimens4 ,label the outside of the wrapped specimen too4 ,take only the best specimens home with you4 ,trim specimens to hand size 7about #b by #c inches74 ,all specimens should be labeled with the following information3 name of mineral or rock type1 where found1 collector's name1 and date4 ,as your collection grows1 you may want to set up a system of cataloging4 ,list specimens and assign a number to each one4 ,place a small amount of white enamel on a corner of each specimen2 when the enamel dries1 number the sample with ,india ink2 coat number with lacquer4 ,corresponding numbers should be entered on your list of specimens4 ,,educational ,,extension ,,program ,this book was prepared by the ,educational ,extension ,section of the ,illinois ,state ,geological ,survey1 principally ,betty ,jean ,hanagan1 ,i4 ,edgar ,odom1 and ,shirley ,j4 ,trueblood1 under the direction of ,george ,m4 ,wilson4 ,they were assisted by other members of the ,survey staff1 especially ,j4 ,e4 ,lamar and ,j4 ,c4 ,bradbury of the ,industrial ,minerals ,section4 ,educational ,extension also serves the public by assembling and distributing rock and mineral collections for ,illinois educational groups1 giving lectures1 preparing exhibits1 answering queries about identification of rocks and minerals1 reporting ,survey news1 and conducting earth science field trips4 ,during each year six field trips are conducted in widely separated parts of the state for teachers1 students1 and laymen4 ,the general program is especially designed to assist in teaching the earth sciences and to help make ,illinois citizens aware of the state's great mineral wealth4 ,illinois ,state ,geological ,survey ,urbana1 ,illinois ,illustration3 ,,illinois ,land of ,lincoln ,transcriber's ,notes --,silently corrected a few typos4 --,retained publication information from the printed edition3 this e,book is public-domain in the country of publication4 --,in the text versions only1 text in italics is delimited by underscores4