Objectives:
Activities:
Outline:
Minerals are naturally occurring, inorganic solid substances, each of which has a definite chemical composition and characteristic crystalline structure, color, and hardness. In the earth's crust, minerals are composed primarily of eight elements -- oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium. Altogether, these elements make up over 98% (by weight) of the earth's crust. Rocks, which make up that part of the earth known as the lithosphere, are bound-together aggregates of one or more minerals. Most rocks are formed from several types of minerals.
Every rock belongs to one of three different rock
groups, depending on how the rock was formed. These three groups
are: (1) igneous rock, (2) sedimentary rock, and (3) metamorphic
rock 
The concept of the rock cycle helps simplify the study of the relationships between the basic rock groups. When studying the rock cycle, note the origin of each group and the processes that transform one group into another.
Let us trace one possible path through the rock cycle. Igneous rock originates deep below the earth's surface as molten material called magma. As magma rises toward the surface, it cools and eventually solidifies into igneous rock. Later, when igneous rock is exposed at the surface of the earth, the rock is subjected to weathering ("weathering" refers to those processes that cause rock to disintegrate or dissolve). Weathered fragments may be removed by erosion and transported by gravity, running water, glaciers, waves, and wind. These weathered rock fragments eventually come to rest as layers of loose, unconsolidated material called sediment. This material may subsequently be subjected to compaction and cementation, causing it to be lithified into solid rock. Sediment is lithified when it is compacted by the weight of overlying layers and cemented as percolating ground water fills pores with mineral matter. The resulting rock is called sedimentary rock. If either sedimentary rock or igneous rock is subjected to intense heat, pressure, or hot fluids, either by being buried deep within the earth or by being subjected to mountain building processes, it becomes metamorphic (or changed) rock. Metamorphism may change a rock so much that the parent rock is unrecognizable, or may change it only slightly so that it is difficult to tell it from its parent material. If a metamorphic rock undergoes even more intense pressure and higher temperatures, it will be transformed into magma and begin the cycle again as an igneous rock.
Igneous rocks form from the cooling and crystallization of hot, molten rock material (or magma). Igneous rocks are further classified according to their "texture" (which refers to the size of their consituent mineral crystals) and their mineral content. The texture of an igneous rock is primarily the result of how quickly the magma from which it formed cooled and solidified. If magma cools rapidly, only small mineral crystals will be able to form (usually too small to be seen without magnification), and the resulting igneous rock will be have a fine texture. But if magma cools slowly, large crystal will be able to form, and the resulting rock will have a coarse texture.
Intrusive (or plutonic) igneous rocks result from the crystallization of magma below the surface of the earth. A large mass of magma at great depth may take thousands of years to reach a solid state. Thus, intrusive igneous rocks have a coarse texture. We are able to see intrusive igneous rocks at the surface only after long periods of erosion have stripped away the overlying earth materials. Extrusive (or volcanic) igneous rocks result from the rapid crystallization of lava (magma that has flowed onto the earth's surface). Thus, extrusive igneous rocks have a fine texture.
Two broad classes of igneous rocks based on mineral content are granitic rocks and basaltic rocks. Granitic rocks tend to be composed of light-colored minerals (minerals containing little iron and/or magnesium) and have a density of about 2.8 g/cm3, while basalts are usually composed of dark-colored minerals (minerals containing more iron and/or magnesium) and have a density of around 3.0 g/cm3. In general, we can think of granitic rocks as making up the continental crust, while basalts are more characteristic of oceanic crust.
Clastic sedimentary rocks originate from the compaction and cementation (or "lithification") of material that was broken away (or "weathered") from preexisting rocks and transported to a place of rest by water, wind, or ice. Rock material that is transported and deposited by water, wind, or ice is called clastic sediment. Clastic sedimentary rocks include conglomerate (lithified gravel-size material), sandstone (lithified sand-size material), and shale (lithified silt- and clay-size material). Important non-clastic sedimentary rocks originate from the material provided by tiny marine organisms that extract calcium bicarbonate from sea water to make their skeletal parts. When these organisms die, their skeletal parts sink to the sea floor as a type of non-clastic sediment. These rocks consist mainly of calcium carbonate (CaCO3); an important example of this type of rock is limestone. Another important, but rare, type of non-clastic sedimentary rock is the evaporite. Evaporites are derived from the evaporation of mainly sea water in enclosed basins. Two of the most common evaporites are rock salt (NaCl) and gypsum (CaSO4 . 2H2O).
Sedimentary rocks are characteristically layered in appearance. These layers, called strata or beds, result from how the original rock-forming material was deposited. Because sedimentary rocks consist of rock material that accumulated on the earth's surface, they often contain records of the environment that existed at the time the sediment was deposited. Thus, sedimentary rocks are particularly important in the interpretation of earth history. Of particular importance are fossils (evidence or remains of prehistoric life), which are found in many sedimentary rock types, particularly limestone, dolostone, and shale.
The classification of metamorphic rocks is determined according to the process that led to the recrystallization of the parent rock. Pressure, high temperatures, and chemically active fluids cause changes to occur deep beneath the earth's surface.
The word metamorphism literally means "changed form". Under great pressures, some minerals become reoriented and aligned at right angles to the pressure. The resulting linear orientation of minerals may give the rock a banded or layered appearance, and the rock is said to be foliated. Where the banding is very fine, the minerals have a flattened, platy structure as exemplified in schists. Where the bands are broad, a rock type known as gneiss (pronounced "nice") is formed. Coarse-grained rocks such as granite generally recrystallize as gneiss, whereas fine-grained rocks like shale and the extrusive igneous types produce schists. Some shales produce a more massive metamorphic rock known as slate. Rocks originally composed of one dominant mineral are not foliated by metamorphism. These are classified as non-foliated or massive. Limestone is reconstituted into much denser marble. The impurities in the limestone produce variegated colors. Silica-rich rocks, such as sandstone are fused into solid sheets of quartz known as quartzite. Quartzite is brittle, but relatively immune to chemical weathering, and commonly forms cliffs and rugged mountain peaks.
Do Exercises A and B
A geologic map shows the age and relationship of
the rocks at the surface of the earth. Below you will find the "Generalized
Geologic Map of Missouri" published by the state Department of Natural
Resources. Much of northern and western Missouri, including the Kansas
City area, is built on layers of sedimentary rock that were formed during
two widely separated intervals of geologic time: the Pennsylvanian Period
and the Quaternary Period. The Quaternary rocks and sediments form
a thin, discontinuous sheet and rest unconformably on the older Pennsylvanian
rocks. The map below does not show the glacial till and loess deposits.
Rocks in the Kansas City area are around 300 million years old, and they consist of beds of limestone and shale with minor amounts of sandstone, coal, and conglomerate. The sediments from which these rocks were made were deposited in a variety of environments including shallow seas, estuaries, lagoons, tidal flats, alluvial plains, and swamps. Each distinct environment was characterized by its own sediment types and ecological niches.
In general, the sediments comprising thick limestone beds, most black and some gray shale beds were deposited in shallow seas during times of marine inundation whereas sediments that comprise most beds of gray shale, sandy shale, sandstone, and thin coal beds represent the deltaic lobes that built outward as the sea withdrew.
Several successive "cycles" of seas rising and shrinking are recorded in the Kansas City rocks. The shoreline marking the boundary the Pennsylvanian sea passed through Kansas City (Heh, beach front property!). The sea was clear and warm and full of life. Invertebrate organisms extracted calcium bicarbonate from the sea water to make their skeletal parts. Shells, spines, plates and other microscopic parts collected on the seafloor to make the richly fossilerous limestone that we see today.
An extensive river system carried large amounts of
sediment eroded from the northern Appalachians, southern Canada and to
a lesser degree from the Ouachita Mounts of Arkansas and eastern Oklahoma.
The loads of sediment were deposited along the shoreline and formed a vast
deltaic complex similar to the present-day Mississippi River delta (see
the figure below). In this delta environment sediment was deposited as
channel sands, flood deposits, and swamp coals. 
Paleogeographic map of the midcontinent of the United States during the
Pennsylvanian Period. The diagram illustrates an instant of time when the
sea was retreating westward. On the deltaic plains, the distributlary channels
became choked with sand, and peat accumulated in swamps between the channels.
Fifty depositional cycles of sea rise and fall are recognized in deep well records and surface exposures in the midcontinent region from Texas to Pennsylvania. The mechanism that produced the repeated fluctuatons of the sea across the low-lying interior of the North American continent has been debated by geologist for over 75 years. A widely accepted scenario attributes the fluctuations in sea level to a combination of factors, including glaciation in the Southern Hemisphere over Gondwanaland, and instability of the continental interior caused by the building of the Appalachian and Ouachita Mountains as the continents collided to form the supercontinent of Pangaea.
Surficial deposits of glacial till (heterogeneous deposits of sediment laid down by glacial ice), stratified outwash (fairly homogeneous deposits of sand and gravel laid down by glacial meltwater), fluvial (stream) deposits, and wind-deposited silt (or"loess") of Quaternary age cover the Pennsylvanian bedrock. The till and outwash, which were probably deposited during the Kansas glacial advance (>600 thousand years), are over 30 ft (9m) thick and cap many of the higher hills in areas north of the Missouri and Kansas Rivers. The till and outwash have been removed by erosion along the valleys of the major tributary streams and in most places to south of the Missouri and Kansas River valleys.
A cover of loess overlies the glacial till and outwash gravels. In places, loess rest on bedrock. The loess bluffs adjacent to the Missouri and Kansas Rivers is over 75 ft (22 m) thick and is well exposed in the face of road excavations along Highway 210. Loess is easily recognized by the brown color and the property of standing in vertical face in excavations. The silt is believed to have been blown from the floodplain of the Missouri by westerly winds during the glacial periods. Within the loess cliffs, buried soil layers stand out as darker colored or reddish layers. These "paleosols" formed during warm "interglacials" between glacial advances.
(Regional Geology, excerpts and modifications from Prof. Dick Gentile, 1994, Field guide book)
(Click on an image for more detail.)
Example
of the loess bluffs near Kansas City, with several paleosols (ancient buried
soils).
Glacial
"erratic". Sample of a metamorphic rock, a quartzite, found
in the glacial till.
Glacial
"erratic". Sample of an igneous rock, a granite, found
in the glacial till. Notice the grooves from the glacier on the rock.
These are called glacial striations.
Do the virtual fieldtrip of the geology of Kansas City
Do Exercise C
Soil is a mixture of inorganic particles (for example, minerals, rock fragments, sand, silt, and clay), organic matter and pore space that is filled with gas and water. Soils have a fairly distinct layering and develop under the influence by climate and living organisms. The layers of a soil are called soil horizons. There are, in general, five soil horizon, though soils don't always contain all five. The five soil horizons are:
Example
of a soil profile in the loess bluffs to the northeast of Kansas City.
Soil texture is a very important soil property.
One reason it is so important is that it largely determines whether precipitation
soaks into the ground and percolates down through a soil too rapidly (leaving
little soil moisture behind for plants to take in through their roots),
too slowly (so that little soil moisture is available for plants to take
in through their roots), or moderately fast (which is what most plants
like best). Soil texture is based on the percentage of sand, silt,
and clay within a soil. The triangle below (called the soil textural
triangle) is used to determine the textural class of different soils.
(Click on the triangle to get a larger and clearer image.) 
Do Exercise D Return to the top of Module 8 Return to WEB-LAB home page
