Science: An Elementary Teacher’s Guide/Rocks, earthquakes, and erosion

Rocks and How They FormEdit


The rocks of Earth's crust are classified into three groups according to their origin. Sedimentary rock are formed from sediments as materials in sand dunes and those that settle to the bottom of lakes and oceans. A sedimentary rock is formed from materials like gravel, sand, and clay carried by rivers and streams to lakes and oceans descend to the bottom and accumulate over long periods of time. One more type of sedimentary rock forms from the remains of plants and animals that live in the ocean. The third type of sedimentary rock includes chemicals such as salt and calcium carbonate these chemicals are deposited out of the water and accumulate on the ocean floor and eventually harden into rock. Igneous rock is formed from magma that comes from within Earth's surface. Extrusive rock cools so quickly that large crystals do not have time to form and extrusive rock is therefore usually glassy or made of very fine crystals. Intrusive rock have large, coarse crystals expected to the slow cooling of the magma. Metamorphic rock forms from igneous or sedimentary rock that has undergone a change in form due to extreme heat. Silicate Minerals Are those that contain the chemical element silicon. this group includes quartz, feldspar, mica, augite, and talc. Nonmetallic Minerals This type of mineral contain metals such as calcium or magnesium. This group includes well-known minerals such as sulfur, rock salt, gypsum, calcite, dolomite, fluorite, and graphite. Metallic Minerals This type of mineral include gold, silver, copper, iron, lead, zinc, aluminum, mercury and titanium. Gem Minerals Are made into precious and semiprecious stones these include diamond, emerald, ruby, and topaz. In geology, rock or stone is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common rock granite is a combination of the quartz, feldspar and biotite minerals. The Earth's outer solid layer, the lithosphere, is made of rock.

Rocks have been used by mankind throughout history. From the Stone Age, rocks have been used for tools. The minerals and metals found in rocks have been essential to human civilization.

There are three major groups of rocks which are igneous, sedimentary, and metamorphic. These rocks undergo a rock cycle and over a period of time they are able to change from one form to another. The scientific study of rocks is called petrology, which is an essential component of geology.

Igneous Rock

Forms through the cooling and solidification of magma or lava. This magma can be derived from partial melts of pre-existing rocks in either a planet's mantle or crust. Typically, the melting of rocks is caused by one or more of three processes: an increase in temperature, a decrease in pressure, or a change in composition.

Two Types of Igneous Rock

  1. Extrusive Rock: Formed from lava (Magma the reaches the Earth's Surface) Types of Extrusive Igneous Rocks: Basalt, Andesite, Rhyolite, Obsidian.
  2. Intrusive Rock: Formed from magma that cools and solidfies beneath the surface. Types of Intrusive Igneous Rocks: Diorite, Gabbro, Granite.

Sedimentary Rock

Are formed at the earth's surface by the accumulation and cementation of fragments of earlier rocks, minerals, and organisms or as chemical precipitates and organic growths in water (sedimentation). This process causes clastic sediments (pieces of rock) or organic particles (detritus) to settle and accumulate, or for minerals to chemically precipitate (evaporite) from a solution. The particulate matter then undergoes compaction and cementation during at moderate temperatures and pressures (diagenesis).

Three types of Sedimentary Rocks

  1. Clastic Sedimentary Rock: Materials such as sand, gravel, silt, clay, cemented together; sandstone
  2. Biological Sedimentary Rock: Remains of plants or animals cemented together; Marine shells and coal.
  3. Chemical Sedimentary Rock: Chemicals dissolved in water that precipitate out; salt and limestone.

Metamorphic Rock

Are formed by subjecting any rock type—sedimentary rock, igneous rock or another older metamorphic rock—to different temperature and pressure conditions than those in which the original rock was formed. This process is called metamorphism; meaning to "change in form". The result is a profound change in physical properties and chemistry of the stone. The original rock, known as the protolith, transforms into other mineral types or other forms of the same minerals, by recrystallization. Types of Metamorphic Rocks: Marble, Slate, Quartzite, Schist.

Check out this awesome experiment or activity that can be done with elementary students:

Chocolate Rock Cycle The Geological Society of London Activity Source: The Geological Society of London. Adapted with permission.

How sweet is this activity? It’s an introduction to the rock cycle using chocolate!

Chocolate can be ground into small particles (weathered), heated, cooled, and compressed — just like rocks. Unlike rocks, chocolate can undergo these processes safely and at reasonable temperatures.

Use your chocolate to create “sedimentary,” “metamorphic,” and “igneous” chocolate. And at the end of it all, make a tasty treat!


Blocks of dark and white chocolate Aluminum foil and/or aluminum foil cupcake holders Hot water and a container to hold it A plastic knife or another simple scraping device Procedure

First, make "sedimentary" chocolate:

1. Scrape some small shavings from your chocolate blocks.

2. Gather these scrapings onto a piece of aluminum foil and press down on them. You might fold the aluminum foil and then press on the chocolate shavings. You could even stand on enclosed foil packages.

3. Observe the joined-together bunch of chocolate scrapings in the foil, which is now similar to sedimentary rock.

Second, make "metamorphic" chocolate:

1. Place a small pile of your sedimentary chocolate, maybe some of your original unused shavings, and a couple of small chunks from your original blocks into aluminum foil or a cupcake holder.

2. Float this concoction on medium hot water.

3. Watch as the heat from the water transfers to the foil and chocolate, which should start to melt.

4. Remove the foil when the chocolate is soft to the touch (for safety, use the plastic knife, not fingers).

5. Let the chocolate cool. The partially melted and cooled chocolate is now similar to metamorphic rock.

Third, make "igneous" chocolate:

1. Place a small pile of sedimentary and metamorphic chocolate and some chunks from the original blocks into your aluminum foil or cupcake holder.

2. Float this concoction on very hot water.

3. Watch as the heat transfers from the water to the foil and melting chocolate. Allow the chocolate to melt until a smooth liquid forms.

4. Carefully remove the molten chocolate and let it cool, still contained in aluminum. Your melted and cooled chocolate is now similar to igneous rock.

Not only fun but tasty!

Earthquakes and How They HappenEdit

An earthquake (also known as a quake, tremor or temblor) is the perceptible shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes can be violent enough to toss people around and destroy whole cities. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time.

2008-05-16 13 21 50 Iceland-Gilsbakki

There are three main types of fault, all of which may cause an interplate earthquake: normal, reverse (thrust) and strike-slip.

Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and movement on them involves a vertical component. Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary. Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.

Mountain by reverse fault

Reverse faults, particularly those along convergent plate boundaries are associated with the most powerful earthquakes, megathrust earthquakes, including almost all of those of magnitude 8 or more. Strike-slip faults, particularly continental transforms, can produce major earthquakes up to about magnitude 8. Earthquakes associated with normal faults are generally less than magnitude 7. For every unit increase in magnitude, there is a roughly thirtyfold increase in the energy released.


Seismology is the scientific study of the seismic waves generated by earthquakes. Seismology is a young science, only about 150 years old. Before scientific studies began, ideas about earthquakes were largely based on myth and superstition. First seismograph in North America is installed at Lick Observatory near San Jose, California. This instrument will later record the 1906 San Francisco earthquake. Application of computers to larger datasets and problems begins in the 1960s: Routine earthquake locations Inverse problems Theoretical seismograms

Earthquakes caused by the shock waves created by shifting plates. These plates can interact in one of 3 ways:

  1. Convergent Movements When plates push into each other
  2. Divergent Movements When plates push away each other
  3. Transform Movements When plates slide by one another


In earth science, erosion is the action of surface processes (such as water flowing or wind blowing) that remove soil, rock, or dissolved material from one location on the Earth's crust, then transport it away to another location. Particulate breakdown of rock or soil into clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by its dissolving into a solvent (typically water), followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimeters, or for thousands of kilometers. Erosion is the process that breaks things down. As far as we're concerned, erosion is the breakdown of the continents and the land around you. The overall effect of breaking down and weathering the land is called denudation. Denudation is the process of erosion. In nature, large things are broken down into smaller things. Boulders become sand. Mountains are rained on and become hills. The pieces of the mountain become smaller pieces and go down the sides of hills. Weathering and erosion always happen in a downhill direction. Erosion is an easy idea to understand. If you see a rock, pull it out of a mountain. Then throw it down on the ground. You are now a part of the erosion of that mountain. You have taken a big object (a mountain) and started to make little objects out of it (a rock). When that rock hit the ground, it could have cracked and made some tiny pieces of rock (sand). Erosion is just that easy. When it rains, the same process happens. Rocks are washed down a mountain or down a stream. Soils are washed away. The ocean beats against a cliff and breaks it apart. They are all examples of denudation.


Weathering causes the disintegration of rock near the surface of the earth. Plant and animal life, atmosphere and water are the major causes of weathering. Weathering breaks down and loosens the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice. There are two types of weathering: mechanical and chemical.

Mechanical Weathering Mechanical weathering is the disintegration of rock into smaller and smaller fragments. Frost action is an effective form of mechanical weathering. When water trickles down into fractures and pores of rock, then freezes, its volume increases by almost 10 percent. This causes outward pressure of about 30,000 pounds per square inch at -7.6 Fahrenheit. Frost action causes rocks to be broken apart into angular fragments. Idaho's extreme temperature range in the high country causes frost action to be a very important form of weathering.

Exfoliation is a form of mechanical weathering in which curved plates of rock are stripped from rock below. This results in exfoliation domes or dome-like hills and rounded boulders. Exfoliation domes occur along planes of parting called joints, which are curved more or less parallel to the surface. These joints are several inches apart near the surface but increase in distance to several feet apart with depth. One after another these layers are spalled off resulting in rounded or dome-shaped rock forms. Most people believe exfoliation is caused by instability as a result of drastically reduced pressure at the earth's surface allowing the rock to expand.

Exfoliation domes are best developed in granitic rock. Yosemite National Park has exceptional examples of exfoliation domes. Idaho has good examples in the Quiet City of Rocks near Oakley as well as in many parts of the granitic Idaho Batholith. In fact, these characteristic rounded forms make rock exposure of the granitic Idaho Batholith easy to identify.

Another type of exfoliation occurs where boulders are spheroidally weathered. These boulders are rounded by concentric shells of rock spalling off, similar to the way shells may be removed from an onion. The outer shells are formed by chemical weathering of certain minerals to a product with a greater volume than the original material. For example, feldspar in granite is converted to clay which occupies a larger volume. Igneous rocks are very susceptible to mechanical weathering.

Chemical Weathering Chemical weathering transforms the original material into a substance with a different composition and different physical characteristics. The new substance is typically much softer and more susceptible to agents of erosion than the original material. The rate of chemical weathering is greatly accelerated by the presence of warm temperatures and moisture. Also, some minerals are more vulnerable to chemical weathering than others. For example, feldspar is far more reactive than quartz.

Differential weathering occurs when some parts of a rock weather at different rates than others. Excellent examples of differential weathering occur in the Idavada silicic volcanic rocks in the Snake River Plains. Balanced Rock and the Gooding City of Rocks are outstanding examples of differential weathering.


Try this quick quiz and test what you have learned by reading this chapter!


1 The two Types of Igneous Rock are?

Intrusive Rock
Extrusive Rock
Both A + B
Volcanic Rock

2 One of the three types of Sedimentary Rocks is?

Phylite Rock
Hornfels Rock
Chemical Sedimentary Rock
Obsidian Rock

3 Earthquake is the ____________ shaking of the surface of the Earth.


4 Exfoliation domes are best developed in what type of rock?

Metamorphic rock

5 True or false? Seismology is a young science, only about 80 years old.