Educational Series 9




                            _INSIDE ILLINOIS
                           Mineral Resources_


                   _Illinois State Geological Survey_

    [Illustration: SEAL OF THE STATE OF ILLINOIS • AUG. 26^TH 1818]

                           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.




                            INSIDE ILLINOIS—
                          _Mineral Resources_


Although Illinois has been nicknamed the “Prairie State,” many parts of
it are hilly and scenic. The idea of large areas of the state being
nothing more than broad, flat prairies has come about because the major
highways have been built to take advantage of the comparatively low,
gently rolling landscape rather than the rougher more scenic areas.

Physiography is the study of the creation and gradual change of land
surface forms (the landscape). Thus, the land surface as we see it today
in each of the physiographic provinces (fig. 1) has had a particular
history of development.

Illinois is about 385 miles long from north to south and about 218 miles
wide. It has an area of 55,947 square miles. The average elevation of
the state is about 600 feet above sea level. Charles Mound, however, in
the northern part of Jo Daviess County in extreme northwestern Illinois,
has an elevation of 1,241 feet above sea level and is the highest point
in the state.

Cheap water transportation is available to Illinois industry through
Lake Michigan, the Illinois Waterway, and the Mississippi, Ohio, and
Wabash Rivers. These major rivers of Illinois collect the surface
drainage of the state from a network of about 500 streams.


WHAT IS THE EARTH MADE OF BENEATH THE GROUND SURFACE?

The earth is made of a large number of different rocks and minerals
(limestone, sandstone, shale, coal, iron, granite, and many others).
These materials are divided into three zones: core, mantle, and crust
(fig. 2).

    [Illustration: Figure 1—Physiographic provinces of Illinois.]

  DRIFTLESS AREA
  WISCONSINAN MORAINES
  ILLINOIAN TILL PLAIN
  MISSISSIPPI RIVER
  WABASH RIVER
  SHAWNEE HILLS
  OHIO RIVER

    [Illustration: Figure 2—The earth with a segment removed to show
    supposed internal zones.]

  Crust (6-30 miles)
  Mantle (1800 miles)
  Outer core (1400 miles)
  Inner core (750 miles)


WHAT IS CORE?

The core is the innermost zone of the earth. It is mainly iron with some
nickel and cobalt. The inner core probably is solid, but the outer core
may consist of the same elements in a molten form. The core is the most
dense (heaviest) of the three zones.


HOW DOES THE MANTLE DIFFER FROM THE CORE?

The mantle, which surrounds the core, is a rigid zone of materials rich
in iron and magnesium. These materials are not as dense as those found
in the core.


WHAT IS THE CRUST OF THE EARTH AND HOW IS IT DISTINGUISHED FROM THE
MANTLE AND THE CORE?

The crust, the top part of which includes the ground we walk on, is the
hard, outer surface layer of the earth. Although the crust is about 6 to
30 miles deep, the scale (size) of figure 2 allows it to be drawn only
as the thin outer line. The rocks and minerals that we are all
acquainted with are found in the crust. These rocks are not as dense and
do not have as high an iron content as do the rocks of the mantle and
the core.


WHAT IS THE EARTH’S CRUST UNDER ILLINOIS MADE OF?

The earth’s crust under Illinois is made of: sedimentary rocks deposited
by water, wind, or glaciers (limestone, sandstone, shale, glacial
drift); igneous, or melted rocks (granite, gabbro); and metamorphic, or
altered sedimentary and igneous rocks (quartzite, gneiss). These various
types of rocks have a relatively thin covering of broken or weathered
material called mantle rock and soil.


WHEN AND HOW WAS THE LAND SURFACE OF ILLINOIS FORMED?

The ground surface over most of Illinois was formed during the ice age
(Quaternary Period) which lasted from about one million years ago up to
nearly 5,000 years ago. As much as 90 percent of the state was covered
by one of several sheets of glacial ice (fig. 3). The glaciers smoothed
down and covered much of the old, rocky, hilly land surface and filled
old valleys with loose, unconsolidated deposits.


WHERE DID THE LOOSE, UNCONSOLIDATED DEPOSITS COME FROM AND WHAT ARE THEY
MADE OF?

In Canada vast thicknesses of snow and ice accumulated until the weight
of the ice finally caused it to flow slowly outward, mainly to the south
(fig. 4). Rocks and surface materials of all types were picked up and
carried by the glaciers for great distances before being deposited.
Pieces of granite, quartzite, and native copper among the many local
rocks and minerals are found in glacial deposits and indicate that at
least part of these deposits came from the Great Lakes Region. The
materials deposited range from clay-size minerals to large boulders.

    [Illustration: Figure 3—Extent of the main glacial advances which
    began with the Nebraskan (a—the oldest) and ended with the late
    Wisconsinan (f—the youngest). Diagram “d” shows the major stream
    development during the time between the Illinoian and the earliest
    Wisconsinan glaciers. The heavy lines on the diagrams indicate major
    stream valleys that were present during these times.]

  a. Inferred limit of NEBRASKAN glaciation
  b. Inferred limit of KANSAN glaciation
  c. ILLINOIAN glacial advance
  d. SANGAMONIAN major drainage
  e. Maximum WISCONSINAN glacial advance
  f. Late WISCONSINAN Valparaiso front and Kankakee Flood


HOW DID ILLINOIS GET ITS SOILS?

    [Illustration: Figure 4—Limits of ice age glaciers.]

Weathering and bacterial decay action have modified many of the loose,
unconsolidated surface materials into soils. The present soils of
Illinois are fertile partly because they have minerals and trace
elements (minute amounts of elements such as copper, zinc, manganese)
brought in by the glaciers from adjacent parts of the country. The
youngest and most fertile soils occur in the northeastern part of the
state and along the Illinois and Mississippi River valleys. These young
soils are more fertile because the glacial deposits and loess
(wind-blown silt) upon which they have developed are younger and
fresher. The minerals and trace elements in these deposits have not been
dissolved out to the extent that they have in the older glacial deposits
and soils in other parts of the state.

    [Illustration: Figure 5—Woolly mammoth (after C. R. Knight).]


ARE ANIMAL AND PLANT REMAINS FOUND IN THE GLACIAL DEPOSITS OF ILLINOIS?

Scattered mammoth (fig. 5) and mastodon remains have been found in
glacial deposits at various localities in the state. Peat, which is an
accumulation of partially decomposed plant materials, has been found,
especially in the northern part of the state. It is marketed as an
organic soil conditioner.




                             MINERAL WEALTH


HOW WEALTHY IS ILLINOIS IN MINERAL PRODUCTION?

In 1963, Illinois mineral production totaled approximately $615,000,000.
This placed the state first as a mineral producer in the Upper
Mississippi Valley and eighth in the nation.


WHAT MINERAL COMMODITIES ARE PRODUCED IN ILLINOIS?

Coal and petroleum, two of the world’s most important mineral resources,
are produced in Illinois. Iron ore, another mineral of extreme
importance, is brought into the steel mills of the Chicago and East St.
Louis areas from deposits in Minnesota and Missouri. Some ore from
foreign countries is also processed in these mills.

A great variety of mineral commodities are produced in Illinois. In the
order of their 1963 value (fig. 6) they are (1) crude oil and natural
gas, (2) coal, (3) clay products, (4) crushed stone and cement, (5)
common sand and gravel, (6) special sands, (7) fluorspar, and (8)
metals—zinc and lead.


HOW MANY ILLINOIS COUNTIES PRODUCE MINERAL COMMODITIES?

In 1963, 99 of the 102 counties of Illinois reported mineral production
of one kind or another.

    [Illustration: Figure 6—Percentage diagram of Illinois mineral
    production value for 1963.]

  Petroleum and Natural Gas  36.3%
  Coal  31.9%
  Stone Products  15.2%
  Clay Products  8.8%
  Sand and Gravel  5.9%
  Fluorspar and Metals  1.9%


HOW MANY PEOPLE WORK IN THE MINERAL INDUSTRIES OF ILLINOIS?

In 1963, approximately 27,000 people worked in mines, quarries, oil
fields, and direct processing operations such as cement and clay
products plants and oil refineries. Many other persons were employed in
transporting the materials and in plants and general offices.


HOW DOES THE FARMER IN ILLINOIS BENEFIT FROM MINERAL PRODUCTION?

The farmers of the state are among those receiving direct and indirect
benefits from Illinois minerals. In 1963, more than 4,800,000 tons of
agstone (crushed limestone and dolomite) were spread on Illinois fields
to reduce acidity, maintain soil fertility, and improve crop production.
Other stone and stone products are used in constructing farm buildings
and facilities and in the maintenance of farm-to-market roads. In
addition, petroleum products and coal provide energy to power the
laborsaving devices that enable the farmer to increase his production
and scale of operations.




                               PETROLEUM


WHAT IS PETROLEUM AND HOW IS IT FORMED?

Petroleum is a dark, oily fluid that is irregularly distributed in
sedimentary rocks throughout the world. There are several ideas about
the origin of petroleum. The most widely accepted of these is that
billions of plants and animals lived and died in widespread seas and
their remains decomposed and released fluid, fatty particles. These were
distilled into “hydrocarbons” (a mixture of the elements hydrogen and
carbon, such as gas and oil).


HOW AND WHERE DID OIL COLLECT IN ROCKS?

The hydrocarbons, or oil and gas droplets, were buried by countless tons
of sediments that accumulated on ancient sea bottoms. As these sediments
hardened into sedimentary rocks, the hydrocarbons were squeezed into
whatever empty spaces were available in the rocks. As the layers of
sedimentary rocks later became folded and broken, oil and gas droplets
and salt water moved upward through any interconnecting open spaces.
Some droplets escaped to the surface as “seeps,” but many were trapped
when they came up against a nonporous barrier. Gas, being lighter than
either oil or water, was trapped at the top, and oil was stopped in the
middle, above the salt water. An accumulation of this kind is termed a
“pool” or a “field.”


WHERE DID OIL ACCUMULATE IN ILLINOIS?

Conditions under which oil is found in Illinois (fig. 7) are as follows:
(a) coral reefs, (b) anticlines (upfolds or arches of rock layers), (c)
“pinching” or “lensing” out of dipping, overlapping porous rock layers,
and (d) buried sandstone-filled ancient stream channels.


ARE THERE LAKES OR RIVERS OF OIL UNDERGROUND?

No. Oil and gas accumulate in the pores (openings) between silt and sand
grains and in small openings in limestone and dolomite.

    [Illustration: Figure 7—Places where oil is found in Illinois: (a)
    coral reefs, (b) anticlines, (c) pinch-outs, and (d) channel
    sandstones.]

  EXPLANATION
  Glacial drift
  Dolomite
  Shale
  Gas saturated zone
  Sandstone
  Oil saturated zone
  Limestone
  Water saturated zone


HOW IS OIL DISCOVERED?

Although prospect (test) drilling is still the only way to prove the
presence or absence of commercial quantities of oil beneath the surface,
careful study by a geologist of all available information may indicate
the most favorable places for testing. Since oil and gas migrate to the
highest parts of the porous rock zones, the geologist tries to find
these high places even though they may be several hundred feet
underground. Sometimes dipping rocks can be seen in outcrops, and
several geophysical methods have been used to indicate where such high
places may occur underground. At other times, high places are found by
studying with a microscope samples of rocks collected from wells already
drilled in the surrounding area. The geologist notes the type and order
of the formations which have been drilled. Many holes have been drilled
based on such information.

Whether or not the test drilling is successful as a producing well,
small samples of cuttings of the rock being drilled are collected and
saved to be studied at a later time. Various instruments are also put
down into the hole to record temperatures, pressures, electrical
properties, and other characteristics of the rocks. This type of
information, when carefully plotted on maps, serves to locate new areas
for test drilling.


HOW MUCH OIL CAN BE OBTAINED FROM AN OIL POOL?

There is no way to tell before a hole is drilled whether or not oil will
be found, how much oil is present, or what will be the best way to get
it to the surface. Where subsurface pressures are great enough, oil may
flow to the surface.

Generally speaking, about one-third of the oil actually present in the
rocks can be pumped before the well becomes uneconomical to operate.
This is called primary production. Oil operators have learned that by
pumping water or gas down some wells into the oil-bearing formation,
another third of the oil may be forced out through neighboring wells.
This is called secondary production. Experiments that use steam or that
burn some of the oil underground in an oil-bearing formation are
attempts to recover the remaining third. These methods using heat are
often referred to as tertiary production methods.


WHAT IS THE “BIGGEST” OIL WELL ON RECORD IN ILLINOIS?

Illinois’ largest well, near Centralia, flowed 12,000 barrels of oil in
a 24-hour period. Most Illinois oil wells, however, have to be pumped,
and the majority of them are now producing 10 barrels or less a day. The
deepest producing well, 5,354 feet, was drilled in 1960 in Wayne County,
near Fairfield. In the same year the deepest oil test was drilled to a
depth of 8,616 feet and was stopped in granite. This test is located in
Fayette County near Beecher City and has its oil production from a zone
over 4,000 feet above the bottom of the hole.


HOW MUCH OIL IS PRODUCED IN ILLINOIS AND HOW VALUABLE IS IT?

In 1963, about 75 million barrels of oil, 2.7 percent of the nation’s
total, were produced in Illinois (fig. 8). This oil is valued at over
$221,000,000.


IS OIL PRODUCTION INCREASING OR DECREASING IN ILLINOIS?

In 1940, our state had its highest yield of oil when 147,647,000 barrels
were produced. Although production figures remained fairly high for some
time, they have declined in the past few years. Since no new large oil
discoveries have been made recently, Illinois’ total known oil reserves
are decreasing yearly. In 1963, Illinois ranked eighth among the
oil-producing states, with 420 oil fields consisting of 30,149 wells.




                                  COAL


WHAT IS COAL AND HOW IS IT FORMED?

Coal is a combustible rock that was formed by the accumulation and
partial decay of vegetation. When coal was forming millions of years
ago, most of the state was a low coastal plain bordered on the west and
southwest by a shallow sea. A large variety of plants grew in great
swamps which covered this coastal plain (fig. 9). When the plants died,
they accumulated in the swamps to form thick masses of peat that were
eventually covered by shallow seas and buried beneath mud and sand.
Periodically, the region was above sea level, new swamps developed, new
peat deposits accumulated, and more sediments were laid down. This
process occurred repeatedly until over 3,000 feet of sediments had been
deposited. Then the sediments were slowly compacted and hardened so that
sandstones, shales, limestones, and coals were formed.

    [Illustration: Figure 8—Estimated total oil production by counties
    from 1888 through 1963.]

  Counties producing oil in January 1965
  Total Production 2,464,758,000 barrels
  46 counties producing

    [Illustration: Figure 9—Reconstruction of coal-forming swamp.]


HOW DO WE KNOW THAT COAL WAS DERIVED FROM PLANT MATERIALS?

Although plant impressions or fossilized wood can be seen in coal, they
are more common in shales and sandstones associated with the coal. Often
roots can be seen in the clay that lies just under the coal, and in some
places stumps of trees from the coal swamp forest are preserved in the
sediments adjacent to the coal (fig. 10). When pieces of coal are
examined with a microscope, carbonized plant remains can be seen.


HOW MANY COAL SEAMS ARE PRESENT IN ILLINOIS?

There are at least 40 different coal seams in Illinois, but most are
relatively thin. Seven coal seams have been mined extensively, and all
together 20 or more have been mined.

    [Illustration: Figure 10—Some root, stem, and leaf fossils found in
    Illinois coal-bearing rocks.]

  _Neuropteris_ ⅖×
  _Nosopteris stem_ ⅔×
  _Neuropteris_ ½×
  _Lepidodendron_ ⅖×
  _Pecopteris_ ⅔×
  _Stigmaria_ ⅖×
  _Annularia_ ⅔×
  _Spiropteris_ ⅔×
  _Sphenophyllum_ 1×


HOW IS ILLINOIS COAL MINED?

In Illinois there are two main ways of mining coal: strip (open-cut) and
underground. Strip or open-cut mines (fig. 11) usually operate where the
coal is at very shallow depths, although such mining is done as much as
100 feet deep or more in some places. Many old underground mines
produced coal from seams that were less than 100 feet deep because they
did not have the large machinery for strip mining when these mines were
started. An abandoned mine, 1,004 feet deep, near Assumption is the
deepest underground coal mine in the state. Coal is now being mined at
depths somewhat over 800 feet in Jefferson County.


HOW DOES ILLINOIS RANK AS A COAL PRODUCER?

Illinois ranks fourth in production of coal in the United States. It is
exceeded only by West Virginia, Kentucky, and Pennsylvania. Some of the
largest and most efficient mines in the country are operated in
Illinois. Underground mines in Illinois have the highest rate of tons
mined per man each day in the country, and this rate is increasing.
Increased mining efficiency has made it possible to hold the price of
coal low enough so that it can successfully compete against other fuels
for many uses.

    [Illustration: Figure 11—Diagram of strip mine showing: (a)
    stripping shovel, and (b) coal-loading shovel.]


HOW MUCH COAL IS PRODUCED IN ILLINOIS ANNUALLY AND HOW VALUABLE IS IT?

In the last 10 years, an average of about 46 million tons of coal has
been mined each year (fig. 12). In 1963, approximately 51.6 million tons
were produced, which were valued at about $196,000,000 at the mine.
Since 1961, strip mines have produced over half of the coal mined in
Illinois.


HOW LONG WILL OUR COAL SUPPLIES LAST?

It will take well over 1,000 years at the present rate of mining in
Illinois to exhaust our coal reserves. An estimated 140 billion tons of
coal in seams of minable thickness remain in the ground in our state;
these are the largest known reserves of bituminous coal of any state in
the United States.


WHAT IS COAL USED FOR?

Electric power generation consumes the greater part of the annual coal
production in Illinois. Coal is also used for home and commercial
heating, for production of coke, and for manufacturing various chemical
compounds from coal tar. Products derived from coal tar include drugs
and medicines, plastics, synthetic fibres, perfumes, flavorings, dyes,
synthetic rubbers, explosives, specialized oils, solvents, wood
preservatives, tarlike paving and roofing materials, and some gas. The
gas is both produced and utilized in the coke industry.


WHAT IS COKE?

Coke is a material produced by burning coal in the absence of air so
that most of the gases and water are driven off without consuming the
solid portion. The resulting solid coke is a strong, porous, combustible
substance.


HOW IMPORTANT IS COKE AND HOW IS IT USED?

The structure and nature of coke make it a valuable fuel for blast
furnace use in the production of steel. In the past, most of the coal
used in the manufacture of coke has come from areas of higher quality
coal outside of our state. However, at present, over 1,000,000 tons of
Illinois coal are mined annually for the production of metallurgical
coke.

    [Illustration: Figure 12—Estimated total coal production by counties
    from 1882 through 1963.]

  Area underlain by coal-bearing rocks
  Counties producing coal in January 1965
  Total Production 3,749,423,534 tons
  71 counties producing




                        STONE AND STONE PRODUCTS


WHAT TYPES OF STONE ARE PRODUCED IN ILLINOIS?

Limestone and dolomite are the most abundant rocks quarried in Illinois.
Small amounts of marble, limestone, and sandstone for building stone are
also produced. In addition, some glacial boulders and cobbles are used
for rock gardens and in home construction. The crushed limestone
industry is Illinois’ most important rock products industry.


WHAT ARE LIMESTONE AND DOLOMITE?

Limestone is a sedimentary rock that consists chiefly of calcite, which
is composed of calcium, carbon, and oxygen. Dolomite is a variety of
limestone that contains considerable magnesium in addition to the other
elements. Limestones were deposited on the floors of ancient seas that
repeatedly covered most parts of Illinois. Shelled creatures, corals,
and coral reefs helped build up the thick limestone deposits (figs. 13
and 14).

    [Illustration: Figure 13—Piece of limestone largely made up of
    fossil brachiopod shells.]


WHERE ARE LIMESTONE AND DOLOMITE QUARRIES LOCATED IN ILLINOIS?

Limestone and dolomite quarries are located along the southern, western,
and northern margins of the state where the thick deposits of these
rocks crop out at the surface. Although bedrock was deposited in
horizontal layers, it has since been downfolded into the Illinois Basin
whose center is in southeastern Illinois. Thus, the thick limestones and
dolomites that are quarried along the margins of the state are too
deeply buried to be quarried in the central part of this basin (fig.
15).

    [Illustration: Figure 14—Fossils commonly found in Illinois rocks.]

  _Strophomena_ 1×
  _Paleoneilo_ 1×
  _Ctenodonta_ ⅔×
  _Dolmanites_ ½×
  _Archimedes_ 1×
  _Hormotoma Polygyra_ 1×
  _Mucrospirifer_ 1½×
  _Atrypa_ ⅔×
  _Crinoid Columnais_ 1×
  _Halysites_ ⅔×
  _Hexagonaria_ 1×
  _Microcylus_ 1×
  _Streptelasma_ ⅔×
  _Lithostrationella_ ½×
  _Lophophyllum_ 1×

    [Illustration: Figure 15—Diagrammatic cross section of the Illinois
    Basin.]

  _MISS. RIVER_
  Waterloo
  Mt. Vernon
  ILLINOIS
  _WABASH RIVER_
  INDIANA
  New Albany
  _OHIO RIVER_


ARE ANY STONE QUARRIES LOCATED IN THE AREA UNDERLAIN BY THE ILLINOIS
BASIN?

Yes. In the area underlain by the basin, stone quarries are operated in
younger, thinner rock strata of Pennsylvanian age. These strata also
overlie the thick limestones and dolomites quarried along the margins of
the state. The quarries located within the basin area produce stone for
agricultural limestone, roads, and other purposes.


HOW AND WHERE ARE LIMESTONE AND DOLOMITE USED?

Millions of tons of stone are crushed annually to produce aggregate for
use in making concrete roads and buildings, for road surfacing, and for
agricultural limestone. Agstone is applied to farmlands to neutralize
soil acidity, improve soil structure, add calcium and magnesium, and
promote conditions favorable for the utilization of soil materials by
plants. Large quantities of limestone are used in making lime and
cement. There are three cement plants in northern Illinois—two at
LaSalle and one at Dixon—and one in southern Illinois, at Joppa.

Small amounts of stone are used for making alkalies and glass, for
railroad ballast, for building stone, for dusting coal mines to prevent
coal dust explosions, and for ingredients in mineral feeds for
livestock.


HOW MUCH STONE DOES ILLINOIS PRODUCE?

A production of about 36 million tons of stone in 1963 was valued at
almost $48,000,000. The cement made from Illinois limestone in the same
year was valued at $32,000,000.




                                  CLAY


WHAT IS CLAY AND HOW IS IT FORMED?

Weathering or alteration of some rocks produces clay which is a very
fine-grained, unconsolidated rock. Clay is made up of a group of
minerals, of which illite, montmorillonite, kaolinite, and chlorite are
the most abundant.


HOW EXTENSIVE ARE CLAY DEPOSITS IN ILLINOIS?

Clay deposits in Illinois consist of Quaternary clays, which were
deposited by glaciers, lakes, and winds; and of fireclay, shale, kaolin,
and “fuller’s earth,” all of which are bedrock deposits. Quaternary
clay, fireclay, and shale resources occur widely in very large
quantities; “fuller’s earth” and kaolin deposits are small in relation
to other clay resources.


HOW IS ILLINOIS CLAY USED?

Surface clay, shale, and fireclay are used in the manufacture of
structural clay products, such as brick, drain tile, and hollow block
(fig. 16). Fireclay is used for a bonding agent in molding sand, for the
making of stoneware vessels, for a plaster on the walls of industrial
furnaces, and for making refractory brick. Refractory brick must be able
to withstand very high temperatures and is used to line industrial
furnaces, boilers, kilns, and ladles for molten steel.

Shale and clay are ground up and mixed with limestone in the manufacture
of cement. Crucibles, refractories, china, and porcelain are made from
kaolin. “Fuller’s earth” is used as a sweeping compound and as an animal
litter.

    [Illustration: Figure 16—Typical Illinois bee-hive kiln.]


WHAT IS THE VALUE OF THE CLAY PRODUCTS MANUFACTURED IN ILLINOIS?

About $53,900,000 worth of clay products were manufactured in Illinois
in 1963.




                            SAND AND GRAVEL


WHERE DO SAND AND GRAVEL COME FROM?

Glacial deposits of sand and gravel are the chief source of these
materials in Illinois, but chert or flint gravels that are older than
the glacial deposits are known and utilized locally in western and
extreme southern Illinois. Sands of recent origin are dredged from
deposits in the larger rivers and streams (fig. 17), and commercial
silica sand is produced from sandstone bedrock.

    [Illustration: Figure 17—Dredge equipment used in producing sand and
    gravel.]


WHAT IS THE VALUE OF COMMON ILLINOIS SAND AND GRAVEL PRODUCTION?

Production of common sand and gravel totaled 27,115,000 tons at a value
of $24,800,000 in 1963.




                              SILICA SAND


WHAT IS SILICA SAND?

Although natural sands are aggregations of many kinds of small rock and
mineral fragments, silica sand consists almost entirely of fine grains
of a single mineral, quartz. The principal sources of Illinois silica
sand are in LaSalle (Ottawa, Utica, Wedron, and Troy Grove areas) and
Ogle (Oregon area) Counties.


HOW IS SILICA SAND USED?

Silica sand, produced in northern Illinois, is famous for its high
purity, and is widely used in making glass. More than two-thirds of the
raw material in common glass is silica sand.

Quantities of silica sand are used as molding sand, because it can
withstand the high temperatures produced in casting steel and other
metals. It also is used for grinding and smoothing plate glass, for sand
blasting, and for fracturing sand used to increase the production of oil
wells. Some silica sand is ground to a fine powder and utilized as an
ingredient in scouring compounds, paint fillers, pottery, glazes, and
enamels.

A specially sized sand is produced from the St. Peter Sandstone
Formation (Ordovician in age) that is used in testing the strength of
cements and as a laboratory standard in various kinds of tests.


HOW VALUABLE IS SILICA SAND TO THE ECONOMY OF THE STATE?

Illinois is a major producer of silica sand, having produced 2,900,000
tons in 1963. The silica sand and ground silica produced in the same
year was valued at $11,400,000.




                                TRIPOLI


WHAT IS TRIPOLI AND WHERE IS IT FOUND?

Tripoli, also known as amorphous silica, is mined in Alexander County in
southern Illinois. It is prepared for market by being ground to a fine
powder. It consists of tiny particles of quartz.


WHAT ARE SOME OF THE USES FOR TRIPOLI?

Tripoli is used as “white rouge” in optical lens polishing, as a paint
filler, as a fine abrasive, in the ceramic industry, and for many other
purposes.




                               FLUORSPAR


WHAT IS FLUORSPAR?

Fluorspar, or fluorite, is a glassy mineral that is commonly gray,
white, or colorless, but may be green, blue, purple, yellow, or black.
It is composed of calcium and fluorine. Fluorite is not a gem because it
is too fragile and soft. Mineral collectors seek it because it is
attractive and because some varieties have the ability to glow under
invisible ultraviolet light (hence the term “fluorescence”).


WHERE ARE FLUORSPAR DEPOSITS LOCATED AND HOW IMPORTANT IS ILLINOIS
PRODUCTION?

Fluorspar produced in the United States comes chiefly from a small area
in Illinois and Kentucky where it has been mined since 1842. Illinois
produced about 66 percent of the nation’s total in 1963. The state’s
production amounted to more than 132,000 tons, valued at about
$6,547,000. The crude ore is extracted from nearly horizontal bedded
deposits and from nearly vertical veins in mines up to 800 feet deep in
Pope and Hardin Counties. Finished fluorspar is produced from the crude
ore by separating and concentrating methods.


WHAT ARE FLUORSPAR PELLETS?

In the separation of fluorspar from the other materials with which it
naturally occurs, a process is used that involves grinding the spar to a
very fine powder. The powdered spar has a number of uses, but to suit it
for use as a flux (a substance which promotes fusion) it is made into
pellets by the use of a binder.


WHAT IS FLUORSPAR USED FOR?

Fluorspar is used extensively as a flux in the steel industry, but over
50 percent of the spar produced in Illinois in 1963 was consumed in the
manufacture of hydrofluoric acid. A large portion of this acid
production is used in the aluminum industry. Hydrofluoric acid is also
employed in the preparation of many fluorine compounds, particularly
those used in the production of fluorocarbons (refrigerants, plastics,
aerosols), insecticides, and high-energy fuels for rockets and missiles.
The fluorocarbons utilize about 40 percent of the hydrofluoric acid
production.




                             LEAD AND ZINC


WHAT ORES YIELD LEAD AND ZINC IN ILLINOIS?

The mineral galena is the principal ore of lead. Galena is gray in
color, very heavy, has a bright metallic luster, and breaks into cubes
along steplike cleavage surfaces (fig. 18). It is composed of lead and
sulfur.

The chief ore of zinc is the mineral sphalerite. It may be brown,
yellow, or black. Sphalerite is a combination of zinc and sulfur, has a
resinous luster, and is not as heavy as galena.


WHERE ARE LEAD AND ZINC MINES LOCATED AND HOW LONG HAVE THESE ORES BEEN
MINED?

Although the lead deposits of extreme northwestern Illinois (now Jo
Daviess County) were reported by the French explorers in 1658 and are
said to have been worked by the Indians, the influx of white settlers in
the early 1800’s marked the beginning of an extensive mining industry,
which was an important factor in the early development of that part of
the state. The town of Galena takes its name from the mineral galena,
which was the principal ore mined.

    [Illustration: Figure 18—Galena cubes.]

In 1845, the Upper Mississippi Valley produced 60 percent of all lead
mined in the United States, which then ranked first in world lead
production. Until about 1860, the zinc ore was considered useless, but
today its total value is several times that of lead.

Lead mining began in southern Illinois in 1842. Lead and zinc production
in this area is a by-product of fluorspar mining.


WHAT IS THE VALUE OF THESE METALS PRODUCED IN ILLINOIS?

In 1963, Illinois produced 20,377 tons of zinc valued at about
$4,677,500 and 2,901 tons of lead worth about $626,600.




                              GROUND WATER


WHAT IS GROUND WATER?

Ground water is water that fills all openings in earth materials in the
zone of permanent saturation. The top of the zone of saturation is
called the water table. The source of ground water is precipitation
(rain and snow) that seeps into the soil and percolates downward. Below
the water table, ground water moves slowly toward places of discharge
such as springs, lakes, rivers, marshes, and wells. Water falls to the
ground, moves through the rocks, returns to the surface, and finally
gets back to the atmosphere by evaporation and from plants (fig. 19).
This cycle is continuously repeated.


WHAT KINDS OF ROCKS YIELD GROUND WATER?

Ground water is most readily obtained from saturated rocks that have
fairly large openings between grains (such as sand, gravel, and
sandstone) or have interconnected cracks or channels (such as
limestones). Rocks that contain ground water and that will yield it to
wells are called aquifers. Sand and gravel beds are widely used aquifers
in Illinois.

    [Illustration: Figure 19—Source, movement, and occurrence of ground
    water. Arrows in aquifers show direction of flow of water.]

  _EVAPORATION_
  SAND AND GRAVEL WELL
  Water Table
  River sand and gravel
  ARTESIAN WELLS
  _EVAPORATION_
  River
  WELL
  COLLECTING AREA FOR ARTESIAN WATER
  PRECIPITATION
  Crater
  WATER TABLE WELL
  _Lake_
  Glacial pebbly clay
  Glacial sand and aquifer
  Shale
  Sandstone aquifer
  Limestone aquifer
  Shale
  GROUND-WATER RESERVOIR


IS WATER FOUND IN UNDERGROUND LAKES AND RIVERS IN ILLINOIS?

No. There are a few large springs that flow from rocks along river
bluffs in Illinois, but most ground water occurs in tiny openings within
the rocks. Ground water reservoirs may be regarded as similar to sponges
rather than as underground lakes or rivers.


WHY DO WELLS SOMETIMES GO DRY?

The water table rises and falls seasonally and from year to year,
depending upon the amount of precipitation. Sometimes the water table
may fall below the bottom of the well or below the pump. Sometimes
overpumping the well or pumping too many wells in a small area lowers
the water table sufficiently to check the yield of the well.


WHAT IS AN ARTESIAN WELL?

An artesian well is one in which pressure forces water to rise in the
well above the level where it was found. In some artesian wells water
flows out at the surface. Conditions for artesian wells are illustrated
in figure 19. The shale above the sandstone and limestone aquifers in
the figure is “tight” and does not permit water to escape upward to the
level at which it enters the aquifers in the intake areas. The water is
under natural pressure. When a well is drilled through the shale and
into the aquifers, water rises, seeking its own level. Most of the deep
wells in northern Illinois are artesian wells, though few of them flow
at the surface anymore.


WILL YOU ALWAYS FIND WATER IF YOU GO DEEP ENOUGH?

This is generally true. However, in much of the southern two-thirds of
Illinois the deeper waters are quite salty. Therefore, only the upper
few hundred feet of rocks are worth exploring for water. In the northern
third of Illinois, where the deepest water wells are located, fresh
water extends in some places to more than 2,000 feet.


HOW CAN GROUND WATER BE FOUND?

The most effective way of locating a ground water supply is by using
knowledge of the geology and ground water conditions—gained partly from
study of existing well records—to determine the most favorable areas and
depths to drill to.

An additional tool that has been used successfully in Illinois is the
electrical earth resistivity survey. The resistivity survey attempts to
locate buried sand and gravel layers that commonly are sources of ground
water. Test drilling is recommended at sites that appear to be underlain
by sand and gravel.

There is no known method that will positively “find” ground water
without drilling.




                    ILLINOIS STATE GEOLOGICAL SURVEY


WHY IS GEOLOGY IMPORTANT?

Geology and allied sciences are being called upon increasingly to aid in
more intelligent and efficient discovery and utilization of mineral
wealth. Our national life and welfare are more and more dependent upon
the further discovery and proper use of the earth’s natural resources.
Illinois is widely recognized by scientists, industrialists, and
educators as being outstanding in its promotion of research and
industrial development.


WHAT ARE SOME OF THE SERVICES AVAILABLE FROM THE SURVEY?

The occurrence and distribution of rock and mineral deposits in Illinois
are studied by the State Geological Survey Division of the Department of
Registration and Education (fig. 20). In seeking new information
concerning the state’s natural mineral resources, physical and chemical
studies of useful rocks, minerals, and mineral products are made.
Techniques and methods are developed and experiments are conducted to
find and prepare Illinois’ mineral substances for use.

The results of the Survey’s field and laboratory findings are published
and made available to all citizens upon request. Much information that
has not been published is in the open files of the Geological Survey
where it may be examined by the public. Members of the Survey’s
scientific and technical staff answer requests for information received
by letter, telegram, telephone, or personal interview.

Since the main ideas of geology are easy to understand and greatly
increase one’s enjoyment and appreciation of the world in which we live,
the Geological Survey publishes popular and educational booklets
designed for the use of Illinois teachers and students. The Survey also
distributes a labeled collection of rocks and minerals for class use in
Illinois schools. Six geological science field trips are conducted each
year throughout various sections of the state for teachers and
interested laymen. Members of the Survey staff give illustrated lectures
to organized groups about the geology and mineral resources of the
state.

    [Illustration: Figure 20—Geological Survey offices are located in
    the Natural Resources Building, Urbana, Illinois.]


WHAT IS THE CHARGE FOR THESE SERVICES?

All of the Survey’s publications are distributed free to schools and
teachers. Only topographic maps and certain base maps, which are
prepared and printed by the U.S. Geological Survey in Washington, are
sold at nominal prices.

    [Illustration: uncaptioned]

    [Illustration: Geologic column]

 Era                                 General Types of Rocks
    Period or System and Thickness
       Epoch

 CENOZOIC “Recent Life”
 Age of Mammals
    Quaternary
    0-500′
       Pleistocene or Glacial Age
                        Recent—alluvium in river valleys
                        Glacial till, glacial outwash, gravel, sand,
                        silt lake deposits of clay and silt, loess and
                        sand dunes; covers nearly all of state except
                        northwest corner and southern tip
    Tertiary
    0-500′
       Pliocene         Chert gravel; present in northern, southern, and
                        western Illinois
       Eocene           Mostly micaceous sand with some silt and clay;
                        present only in southern Illinois
       Paleocene        Mostly clay, little sand; present only in
                        southern Illinois
 MESOZOIC “Middle Life”
 Age of Reptiles
    Cretaceous          Mostly sand, some thin beds of clay and,
    0-300′              locally, gravel; present only in southern
                        Illinois
 PALEOZOIC “Ancient Life”
 Age of Amphibians and Early Plants
    Pennsylvanian       Largely shale and sandstone with beds of coal,
    0-3,000′            limestone, and clay
    (“Coal Measures”)
    Mississippian       Black and gray shale at base; middle zone of
    0-3,500′            thick limestone that grades to siltstone, chert,
                        and shale; upper zone of interbedded sandstone,
                        shale and limestone
    Age of Fishes
    Devonian            Thick limestone, minor sandstones and shales;
    0-1,500′            largely chert and cherty limestone in southern
                        Illinois
    Age of Invertebrates
    Silurian            Principally dolomite and limestone
    0-1,000′
    Ordovician          Largely dolomite and limestone but contains
    500-2,000′          sandstone, shale, and siltstone formations
    Cambrian            Chiefly sandstones with some dolomite and shale;
    1,500-3,000′        exposed only in small areas in north-central
                        Illinois
 ARCHEOZOIC and PROTEROZOIC
                        Igneous and metamorphic rocks; known in Illinois
                        only from deep wells

    [Illustration: uncaptioned]

                   _Illinois State Geological Survey
                         Educational Series 9_




                          Transcriber’s Notes


—Silently corrected a few typos.

—Retained publication information from the printed edition: this eBook
  is public-domain in the country of publication.

—In the text versions only, text in italics is delimited by
  _underscores_.