assembled from web sources by e. o’connor, ph.d. / instructional supplement available rocks –...

Assembled from web sources by E. O’Connor, Ph.D. / Instructional supplement available

Rocks – Almost As Old As the Earth

“The Earth is made of rock, from the tallest mountains to the floor of the deepest ocean. Thousands of different types of rocks and minerals have been found on Earth. Most rocks at the Earth's surface are formed from only eight elements (oxygen, silicon, aluminum, iron, magnesium, calcium, potassium, and sodium), but these elements are combined in a number of ways to make rocks that are very different.

Rocks are continually changing. Wind and water wear them down and carry bits of rock away; the tiny particles accumulate in a lake or ocean and harden into rock again. The oldest rock that has ever been found is more than 3.9 billion years old. The Earth itself is at least 4.5 billion years old, but rocks from the beginning of Earth's history have changed so much from their original form that they have become new kinds of rock. By studying how rocks form and change, scientists have built a solid understanding of the Earth we live on and its long history.

Rock-forming and rock-destroying processes have been active for billions of years. . . In a simple rock collection of a few dozen samples, one can capture an enormous sweep of the history of our planet and the processes

that formed it.”

Image and text from: http://interactive2.usgs.gov/learningweb/explorer/topic_rocks.htm


Different Types of Rocks

“Geologists classify rocks in three groups, according to the major Earth processes that formed them. The three rock groups are igneous, sedimentary, and metamorphic rocks. Anyone who wishes to collect rocks should become familiar with the characteristics of these three rock groups. Knowing how a geologist classifies rocks is important if you want to transform a random group of rock specimens into a true collection.”

Text from: http://interactive2.usgs.gov/learningweb/explorer/topic_rocks.htm ;

Image from: http://www.fi.edu/fellows/payton/rocks/create/index.html


Sedimentary Rock Formation

“For thousands, even millions of years, little pieces of our earth have been eroded--broken down and worn awayby wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock.”

Image animation is from: http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

If you seeing this information from a PowerPoint presentation or if you click on the web link listed below,

you will see this image as an animation that shows sedimentary rock formation.


Sedimentary Rock – Some Examples

“Sandstone rocks are sedimentary rocks made from small grains of the minerals quartz and feldspar. They often form in layers as seen in this picture. They are often used as building stones.”

Image and text is from: http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

“Limestone rocks are sedimentary rocks that are made from the mineral calcite which came from the beds of evaporated seas and lakes and from sea animal shells. This rock is used in concrete and is an excellent building stone for humid regions.”



“Shale rock is a type of sedimentary rock formed from clay that is compacted together by pressure. They are used to make bricks and other material that is fired in a kiln.”

Image and text is from links to: http://www.fi.edu/fellows/payton/rocks/create/sediment.htm

“Conglomerate rocks are sedimentary rocks. They are made up of large sediments like sand and pebbles. The sediment is so large that pressure alone cannot hold the rock together; it is also cemented together with dissolved minerals.”



“Gypsum rocks are sedimentary rocks made up of sulfate mineral and formed as the result of evaporating sea water in massive prehistoric basins. It is very soft and is used to make Plaster of Paris, casts, molds, and wallboards.”

Image and text is from links to: http://www.fi.edu/fellows/payton/rocks/create/sediment.htm


Sedimentary Rocks – More Detail“Sedimentary rocks are formed at the surface of the Earth, either in water or on land. They are layered accumulations of sediments: fragments of rocks, minerals, or animal or plant material. Temperatures and pressures are low at the Earth's surface, and sedimentary rocks show this fact by their appearance and the minerals they contain. Most sedimentary rocks become cemented together by minerals and chemicals or are held together by electrical attraction; some, however, remain loose and unconsolidated. The layers are normally parallel or nearly parallel to the Earth's surface; if they are at high angles to the surface or are twisted or broken, some kind of Earth movement has occurred since the rock was formed. Sedimentary rocks are forming around us all the time. Sand and gravel on beaches or in river bars look like the sandstone and conglomerate they will become. Compacted and dried mud flats harden into shale. Scuba divers who have seen mud and shells settling on the floors of lagoons find it easy to understand how sedimentary rocks form.


Common sedimentary rocks include sandstone, limestone, and shale. These rocks often start as sediments carried in rivers and deposited in lakes and oceans. When buried, the sediments lose water and become cemented to form rock.”

Bonus question: why do you think these scientists put a pen in the picture?


Igneous Rock Formation

“ Igneous rocks are called fire rocks and are formed either underground or above ground. Underground, they are formed when the melted rock, called magma, deep within the earth becomes trapped in small pockets. As these pockets of magma cool slowly underground, the magma becomes igneous rocks. Igneous rocks are also formed when volcanoes erupt, causing the magma to rise above the earth's surface. When magma appears above the earth, it is called lava. Igneous rocks are formed as the lava cools above ground.”

Image animation and text is from: http://www.fi.edu/fellows/payton/rocks/create/igneous.htm


you will see this image as an animation that shows igneous rock formation.


Igneous Rock – Some Examples

“Granite rocks are igneous rocks which were formed by slowly cooling pockets of magma that were trapped beneath the earth's surface. Granite is used for long lasting monuments and for trim and decoration on buildings.”

Images and text are from links to: http://www.fi.edu/fellows/payton/rocks/expert/igneous.htm

“Scoria rocks are igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. Scoria is actually a kind of glass and not a mixture of minerals.”


Igneous Rock – Some Examples“Pumice rocks are igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. This rock is so light, that many pumice rocks will actually float in water. Pumice is actually a kind of glass and not a mixture of minerals. Because this rock is so light, it is used quite often as a decorative landscape stone. Ground to a powder, it is used as an abrasive in polish compounds and in Lava© soap.”

Images and text are from links to: http://www.fi.edu/fellows/payton/rocks/expert/igneous.htm

“Obsidian rocks are igneous rocks that form when lava cools quickly above ground. Obsidian is actually glass and not a mixture of minerals. The edges of this rock are very sharp.”


Igneous Rocks – More Details“Igneous rocks, also called volcanic rocks, are formed from melted rock that has cooled and solidified. When rocks are buried deep within the Earth, they melt because of the high pressure and temperature; the molten rock (called magma) can then flow upward or even be erupted from a volcano onto the Earth's surface. When magma cools slowly, usually at depths of thousands of feet, crystals grow from the molten liquid, and a coarse-grained rock forms. When magma cools rapidly, usually at or near the Earth's surface, the crystals are extremely small, and a fine-grained rock results. A wide variety of rocks are formed by different cooling rates and different chemical compositions of the original magma. Obsidian (volcanic glass), granite, basalt, and andesite porphyry are four of the many types of igneous rock.


Common igneous (volcanic rocks) are basalt, andesite, and rhyolite. When magmas crystallize deep underground they look different from volcanic rocks because they cool more slowly and, therefore, have larger crystals. Igneous rocks cooled beneath the Earth's surface are called intrusive rocks. The intrusive equivalents of basalt, andesite, and rhyolite are gabbro, diorite, and granite, respectively.”


Metamorphic Rock Formation

“Metamorphic rocks are rocks that have "morphed" into another kind of rock. These rocks were once igneous or sedimentary rocks. How do sedimentary and igneous rocks change? The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change. If you exam metamorphic rock samples closely, you'll discover how flattened some of the grains in the rock are.”

Image animation and text is from:

http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm


you will see this image as an animation that shows metamorphic rock formation.


Metamorphic Rock – Some Examples

“Schist rocks are metamorphic. These rocks can be formed from basalt, an igneous rock; shale, a sedimentary rock; or slate, a metamorphic rock. Through tremendous heat and pressure, these rocks were transformed into this new kind of rock.”

Image and text is a link from: http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm

“Gneiss rocks are metamorphic. These rocks may have been granite, which is an igneous rock, but heat and pressure changed it. You can see how the mineral grains in the rock were flattened through tremendous heat and pressure and are arranged in alternating patterns.”


Metamorphic Rocks – More Details“Sometimes sedimentary and igneous rocks are subjected to pressures so intense or heat so high that they are completely changed. They become metamorphic rocks, which form while deeply buried within the Earth's crust. The process of metamorphism does not melt the rocks, but instead transforms them into denser, more compact rocks. New minerals are created either by rearrangement of mineral components or by reactions with fluids that enter the rocks. Some kinds of metamorphic rocks--granite gneiss and biotite schist are two examples--are strongly banded or foliated. (Foliated means the parallel arrangement of certain mineral grains that gives the rock a striped appearance.) Pressure or temperature can even change previously metamorphosed rocks into new types.


Common metamorphic rocks include schist, marble, and gneiss. Sedimentary rock shale (formed mostly of clay sediments) when buried and heated to high temperatures (300-500°C) becomes transformed or metamorphosed into schist.”


What is the Rock Cycle?

Image and text from: http://imnh.isu.edu/digitalatlas/geo/basics/diagrams.htm

“Like most Earth materials, rocks are created and destroyed in cycles. The rock cycle is a model that describes the formation, breakdown, and reformation of a rock as a result of sedimentary, igneous, and metamorphic processes. All rocks are made up of minerals. A mineral is defined as a naturally occurring, crystalline solid of definite chemical composition and a characteristic crystal structure. A rock is any naturally formed, nonliving, firm, and coherent aggregate mass of solid matter that constitutes part of a planet.”


NY State Geologic Map- This map shows the type of rocks found in the different regions of New York; although the information is complex, you can easily

see the patterns where various rocks are found. What do you think these patterns tell us about the geographic features of New York? Do any patterns appear familiar? You can go to the link

below if you are interested is seeing the interesting details about New York and its geologic history .

http://geology.about.com/library/bl/maps/newyorkmapmid.jpg?once=true&


Lesson on the Rocks & Rock Formation

• The following information has been compiled from a number of government and education web sites (the links are shown on the pages)

• This information is provided in print format for students who can not access the web sites directly

• This information will serve as background text to several school lessons

• Students should be encouraged to access the web sites themselves (links are provided on the pages) so they can explore more about these topics; a more comprehensive list of web sites is available through http://www.ils-courses.net/rocks


More Information on Geology

• See http://www.ils-courses.net/rocks for more links to geology information and a companion web site that is associated with Dr. O’Connor’s work on this geology unit

• You can reach Dr. Eileen O’Connor at: [email protected]

assembled from web sources by e. o’connor, ph.d. / instructional supplement available rocks –...

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