The Rock Cycle EarthCache
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This is a one of a kind outdoor exhibit on the main campus of Santa Fe College in Gainesville, Florida. It features over twenty boulders, many weighing thousands of kilograms. These boulders were collected from different localities across the U.S.A.
As this is taking you to an exhibit rather than a natural location, there will be more questions than most earthcaches have.
The rock cycle is a concept used to explain how the three basic rock types are related and how Earth processes, over geologic time, change a rock from one type into another. Plate tectonic activity, along with weathering and erosional processes, are responsible for the continued recycling of rocks. Rocks are classified into three basic types based on how they formed.
Igneous - A rock formed by the cooling and crystallization of magma (molten rock) at or below the Earth's surface.
Sedimentary - A rock formed as a result of the weathering process, either by compaction and cementation of rock and mineral fragments, or the precipitation of dissolved minerals.
Metamorphic - These rocks form as existing rocks are subjected to intense heat and/or pressure, usually over long periods of time.
The rocks on display are meant to be viewed in a clockwise direction. As you walk, keep in mind that existing rocks may change through natural processes over geologic time, or even melt to form new rocks.
Igneous Rocks
The oldest type of all rocks is the igneous rock (IG nee us). The word "igneous" comes from a Greek word for fire. Deep inside the earth, the temperature is very high and the minerals there are in liquid form called magma. As the magma pushes towards the earth's surface, it starts to cool and turns into solid igneous rock.
All igneous rocks do not cool the same way. That is why they do not look all the same. Some cool slowly, deep under the earth's surface. These are called intrusive igneous rocks. The slow cooling formed rocks with large crystals.
Other rocks formed when the magma erupted from a volcano or reached the earth's surface through long cracks. Magma is called lava when it reaches the earth's surface. Lava cools quickly and forms rocks with small crystals. They are called extrusive igneous rocks. Obsidian is an example of an extrusive igneous rock that cooled so fast that it has no crystals and looks like shiny, black glass.
Sedimentary Rocks
The earth's surface is constantly being eroded, causing rocks to be broken up into smaller pieces by weathering agents such as wind, water, and ice. These small pieces of rock turn into pebbles, gravel, sand, and clay which settle into new places and begin to pile up, forming layers. Over a long period of time, the pieces become pressed together and form solid rock called sedimentary rock. Most sedimentary rocks form under water. Seventy percent of the earth is covered by water now and most of the earth has been covered by water at some point in the past, so sedimentary rocks are common all over the world and are common sources of fossils.
Sediments can harden into sedimentary rock in two ways; pressure where layer after layer of sediments are deposited, the lower layers are pressed together tightly under the weight of the layers above or cementing where the sediments are "glued" together by minerals dissolved in the water.
Some examples of sedimentary rocks are sandstone, limestone, conglomerate, and shale. Sandstone is formed from grains of sand pressed tightly together and are formed from the sand on beaches, in riverbeds, and sand dunes. Sandstones are usually made of the mineral quartz. Limestone is formed from tiny pieces of shells of dead sea animals that have been cemented together. Conglomerate contains sand and rounded pebbles that have also been cemented together. Shale is formed from mud or clay that has been pressed together. Shale forms in quiet waters such as swamps and bogs. Sedimentary rocks are generally easy to identify because you can see the layers.
Metamorphic Rocks
Heat and pressure can change many things. They can even change rocks. The name for rocks that has been changed is metamorphic (met uh MOR fik) rocks. Metamorphic comes from Greek words meaning "change" and "form".
Metamorphic rocks form deep in the earth where high temperature, great pressure, and chemical reactions cause one type of rock to change into another type of rock. Metamorphic rocks begin to form at 12-16 kilometers beneath the earth's surface. They begin changing at temperatures of 100 degrees Celsius to 800 degrees Celsius. If you squeeze and heat a rock for a few million years, it can turn into a new kind of rock.
The heat required to form metamorphic rocks comes from magma and the pressure comes from layers of rock piled on top of layers and layers of rock. The thicker the layers, the more pressure there is.
Foliation refers to repetitive layering in metamorphic rocks. Each layer may be as thin as a sheet of paper, or over a meter in thickness. It is caused by shearing forces (pressures pushing different sections of the rock in different directions), or from higher pressure from one direction than others. The layers form parallel to the direction of the shear, or perpendicular to the direction of higher pressure. Nonfoliated metamorphic rocks are typically formed in the absence of significant differential pressure or sheer.
To log this earth cache, you will need to stop and look at each of the rocks and answer questions based on information listed on the signs and observations of the rocks. This will be able to be completed without the need to look up additional information online, however you are encouraged to learn more than is necessary for the cache and should feel free to utilize additional resources as you see fit.
Please email your answers to me for the following questions for the Earthcache. Any logs that do not have an email sent with the answers will be deleted. Please do not post pictures of the individual rocks, but feel free to post a picture of you near the Rock Cycle sign (NOT a requirement of logging the cache)
1) Which of the igneous rocks are intrusive and which are extrusive?
2) Which of the metamorphic rocks here exhibit foliation and which of the rocks appears to have had the most intense forces acting on it causing the foliation?
3) Which type of rock would be the most likely type to find fossils in? Why?
4) Which of the sedimentary rocks was used by Native Americans to make arrowheads, spear points, knives, axes and other tools?
5) What is the chemical change that forms the rock from question 4?
6) What caused the differences between the 2 examples of Ocala Limestone?
7) Visit the rocks at the two waypoints in the listing. What are the two rocks and how do the "layers" in the rocks differ and why are they different based on how they formed?
Additional Hints
(No hints available.)
Treasures
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