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Do you like rocks? If so, you are a rock hound, a person who collects and studies rocks
and minerals. Since the beginning of time rocks and minerals have been used as a way to
study the earth's history and as tools or jewelry (visit the Smithsonian Gem & Mineral
Collection to see the Hope Diamond, a Spanish Inquisition Necklace, and other pieces
of jewelry). Geologists, like Dr. Tom Broadhead at the
University of Tennessee, Knoxville, are scientists who study rocks to learn more about our
Earth.
There are different types of geologists:
Although collecting rocks is fun, that's not the only reason scientists do it.
By studying rocks scientists can learn where to build houses, roads, bridges, and other
buildings. For example, earthquakes occur along faults.
Scientists can determine the location of fault lines so we don't build our houses along
the lines. Also, lighthouses built along coasts centuries ago are being moved today
because rock cliffs between them and the ocean have eroded away.
"Earthquakes, volcanic activity, and floods are not new. These things have been
happening for years and years. By studying the physical history of the earth, geologists
are able to see what happened in the past and build models that predict what could happen
in the future," Dr. Broadhead says.
Scientists also study rocks to learn about the history of the natural world. Animals that
existed millions of years or even just hundreds of years ago aren't around today. An
example is a Dodo bird. Dodo birds were hunted to extinction, but there are other animals,
like dinosaurs, that are extinct for other reasons. By studying the fossils of these
animals, scientists can try to determine what the animal looked like when it was alive,
what types of food it ate, how it died, and why it became extinct.
There are three basic types of rocks: sedimentary, igneous, and metamorphic.
Sedimentary rocks are made up of layers of silt, small pieces of other rocks, and
sometimes the skeletons of tiny creatures. One example of a sedimentary rock is the chalk
you use at school. Another example is limestone, one of Tennessee's state rocks. The rocks
you see inside caves are made of limestone. The Grand Canyon is made up of sandstone,
limestone, and shale that have been eroded by the Colorado River to form the Canyon as it
is today.
Igneous rocks started as molten magma or lava and then cooled to become rock.
Coarse grained rocks are formed when the lava cools slowly and fine grained rocks from
when it cools faster. Some examples of igneous rocks are granite and peridotite. The
Hawaiian islands are made of cooled volcanic lava called basalt. One of the most popular
igneous rocks is an Apache Tear.
Metamorphic rocks are rocks that have been changed by heat or pressure while
forming. Sedimentary and igneous rocks can become metamorphic rock. Slate is used in
blackboards, talc in talcum power, and soapstone for carving.
According to Dr. Broadhead, different types of rocks can be found in
different places in North America.
"If you go into Northern Canada, most of the rocks you find will be igneous or
metamorphic. If you go down south into the US, most of what you find on the surface is
going to be sedimentary rock.
"I consider Tennessee to be a fabulous natural laboratory. On the far eastern edge of
the state we have some igneous and metamorphic rocks that are about 700 million years old.
At the other end of the state, near the Mississippi River, sediment is being deposited
now. In between you have lots of geology exposed at the surface.
"In East Tennessee you have the
Appalachian Mountains including the Blue Ridge which are mainly metamorphic with a little
igneous rock.
"In the folded Appalachians, where
Knoxville is located, there are valleys and ridges. The ridges are made of sandstone
that is resistent to erosion. The valleys are shales and limestones that erode very
easily.
"Farther to the west, at the Cumberland
Plateau, the rocks are mainly flat lying. There are spectacular examples of
sedimentary rocks that were deposited as river channel deposits in river deltas.
"The Nashville area is at the edge
of the Highland Rim and in the Central Basin. There are rocks the same age as the rocks
you see in Knoxville, but the rocks are flat lying instead of being folded and faulted
like the ones in East Tennessee.
"Past the western highland rim and into the western valley, there are much younger
rocks of Cretaceous and Cenozoic age."
Remember anytime you go hunting for rocks, safety comes first.
See first what you can find in your own yard or school playground.
When the farm fields, particularly in East Tennessee, have been plowed, you can sometimes
see ridges of rocks sticking out of the ground. Lots of times there are limestone beds in
those fields where fossils can be found.
The mountains are good places. Because there isn't a lot of vegetation, there are rocks
like sandstone and slate exposed.
In places where roads have been cut through the rock, there can be spectacular exposures
of different kinds of rocks and fossils. Be very careful of traffic. In some states it is
illegal to stop on the interstate highway to collect rocks.
Check to see if a college or university near you offers a course on rock hunting.
Visit your local rock shop.
Many areas have gem and mineral clubs that hold monthly meetings, take field trips to
collect rocks, and organize rock shows.
Every state in the United States has a state rock. Tennessee has two. One is limestone and
the other is agate. One of the best examples of limestone in Tennessee is called
"Tennessee Marble." Tennessee marble (not a true marble because it is not
metamorphic rock) can be found in many of the buildings across the state like the Federal
Court building in Knoxville and in the sculpture "Terra"
at the University of Tennessee. The National Gallery of Art in Washington is also made of
Tennessee limestone.
What is your state rock? If you don't know, check your local library.
Suggested reading list and other Internet resources.
Written by Tina Jones, Fall 1996
