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 neighbourhood.
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.
Written by Tina Jones, Fall 1996
The University of Tennessee, Knoxville