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The rock cycle is an illustration that is used to explain how the three rock types are related to each other and how Earth processes change a rock from one type to another through geologic time. Plate tectonic movement is responsible for the recycling of rock materials and is the driving force of the rock cycle.

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Rock Cycle - Rocks (3A)
Pre Lab

OBJECTIVES:

Comparing sedimentary, igneous, and metamorphic rocks.

Exploring the etymology of sedimentary, igneous, and metamorphic.

VOCABULARY:

igneous

metamorphic

sedimentary

MATERIALS:

Students learn the meaning of the words igneous, sedimentary, and metamorphic.

Schist, a metamorphic rock in thin section.

BACKGROUND:
Minerals make up rocks. Rocks are formed in many environments upon and within the Earth's crust. There are three types of rock, each formed in a different way. Igneous rock , formed by the cooling of magma (molten rock) inside the Earth or on the surface. Sedimentary rocks, formed from the products of weathering by cementation or precipitation on the Earth's surface. Metamorphic rocks, formed by temperature and pressure changes inside the Earth. All three types of rock make up the Earth's lithosphere, the outermost layer. The lithosphere averages about 100 kilometers in thickness.

All igneous rocks began as magma (molten rock) which cooled and crystallized into minerals. Geologists classify igneous rocks based on both their crystal size and composition. Igneous rocks may look different because they may have cooled at different rates and the "mother" magma (original melted rock) was of a different composition. Variations in these two factors have created many different types of igneous rocks. When the magma cools at different rates, it creates different sized minerals. Quick cooling magmas have small minerals (with the exception of obsidian, which is actually composed of silica, but has no crystalline structure). Basalt, for example, has small minerals, most of which can only be seen under a microscope. Quick cooling lavas are called volcanic rocks. Magma that cools slowly creates rocks like granite, which have large minerals that can be seen with the naked eye. These igneous rocks cool inside the lithosphere, and are called plutonic rocks.

Sedimentary rocks form at the Earth's surface in two main ways. Clastic material (pieces of other rocks or fragments of skeletons) may become cemented together and chemical precipitation and evaporation can form sedimentary rocks. Sedimentary rocks are usually associated with liquid water (which facilitates erosion, transportation, deposition, and cementation). However, sedimentary rocks may also form in dry, desert environments or in association with glaciers.

Metamorphic rocks are igneous, sedimentary, or preexisting metamorphic rocks that have been changed by great pressures and temperatures within the crust and upper mantle of the Earth. The temperatures were not enough to melt the rock, otherwise, an igneous rock would have formed. The pressures were much greater than those required to simply break the rocks into pieces. They were high enough to change the chemical make up of the rock by forcing the elements in it to "exchange partners." Different grades of temperature and pressure will cause the same original rock to form very different metamorphic rocks. Slate, which forms from the sedimentary rock shale, is very dense, smooth and does not contain visible minerals. However, if more pressure and temperature are applied to a slate, it could turn into schist, which has visible layers of minerals. If yet higher temperature and pressure are applied, the schist could turn into gneiss, which shows visible bands of minerals.
PROCEDURE:
Review with students where igneous, sedimentary, and metamorphic rocks are formed using the diagram below.

1. Ask students to find words which have ign-, sediment-, and metamorphor- roots. This may wish to use children's dictionaries, encyclopedias or other similar resources. This will help the students remember the meaning of the words igneous, sedimentary, and metamorphic. Here are some examples, along with suggestions for how to explain rocks to the students.
IGNEOUS -Fire or hot rocks, form when melted rock (magma or lava) cools. When magma cools slowly, large minerals are produced. In lava that cools quickly the minerals can only be seen with a microscope. IGN = Latin for fire

ignite
ignescent
ignis fatuus
ignition
ignitron
igniter

SEDIMENTARY - Sedimentary rocks are usually formed under water when grains of broken rocks are glued together. SEDIMENT = Latin meaning to settle

sedimentology
sedimentation

METAMORPHIC - Metamorphic rocks are rocks that once were igneous or sedimentary rocks but have been changed by pressure and temperature. META = from Latin and Greek meaning to transform; MORPH = Greek meaning form

metamorphism
metamorphose

2. Students can also develop nicknames for the rocks, and they can call the individual types of rocks: IGNEOUS - fire or hot; SEDIMENTARY - cool, wet, fossil; METAMORPHIC - flat, squished, changed

3. Using the Mineral and Rock Kit, show the students examples of the different types of rocks.Use the rocks in the kit to see if students remember what formed each of them. The written packet included with the kit should be consulted for more information on each rock.

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Exploring the Etymology of Sedimentary, Igneous, and Metamorphic Rocks

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Rock Cycle - Rocks (3A) Pre Lab OBJECTIVES: Comparing sedimentary, igneous, and metamorphic rocks. Exploring the etymology of sedimentary, igneous, and metamorphic. VOCABULARY: igneous metamorphic sedimentary MATERIALS: Students learn the meaning of the words igneous, sedimentary, and metamorphic. Schist, a metamorphic rock in thin section. BACKGROUND: Minerals make up rocks.

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The Rock Gallery contains pictures and descriptions of common igneous, metamorphic, and sedimentary rocks. The igneous rocks, like the granite that makes up half Dome, in Yosemite National Park, pictured above, are listed at the top of the page followed by metamorphic rocks. The sedimentary rocks are at the bottom of the page.

The following is an example of igneous rocks. It is not an all inclusive list but a brief pictorial list of some common igneous rocks.

All pictures of igneous rocks are courtesy of the USGS - United States Geological Survey with the exception of granite. Discriptions are adapted from the USGS. The table below shows examples of common metamorphic rocks. Clicking on the name of the rock will bring up a larger picture and a description of the rock type in a new window.

The table below shows examples of common clastic sedimentary rocks. They are listed by grain size in decending order. Grain size is one factor in classifying sedimentary rocks. Clicking on the name of the rock will bring up a larger picture and a description of the rock type in a new window.

Igneous metamorphic sedimentary rock are the three main types of rock on earth. Read more about Igneous Metamorphic Sedimentary Rock:

Igneous Rocks

Metamorphic Rocks

Sedimentary Rocks

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The Rock Gallery has Igneous Metamorphic Sedimentary Rock Photos and Text

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The Rock Gallery contains pictures and descriptions of common igneous, metamorphic, and sedimentary rocks. The igneous rocks, like the granite that makes up half Dome, in Yosemite National Park, pictured above, are listed at the top of the page followed by metamorphic rocks. The sedimentary rocks are at the bottom of the page.

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As a terrestrial planet, Earth is divided into layers based on their chemical and rheological properties. And whereas its interior region - the inner and outer core - are mostly made up of iron and nickel, the mantle and crust are largely composed of silicate rock. The crust and upper mantle are collectively known as the lithosphere, from which the tectonic plates are composed.

It in the lithosphere that rocks are formed and reformed. And depending on the type of rock, the process through which they are created varies. In all, there are three types of rocks: igneous, sedimentary, and metamorphic. Each type of rock has a different origin. Therefore, the question, "How are rocks formed?" begs three distinct answers.

How Are Igneous Rocks Formed?

Igneous rocks are formed when melted rock cools and solidifies. Melted rock may come in the form of magma, when it is found underneath the Earth's surface. It can also come in the form of lava, when it is released unto the Earth's surface during a volcanic eruption. Some examples of igneous rocks are granite, scoria, pumice, and obsidian.

Pumice, for instance, is formed when lava made up of melted rock, water, and trapped gas is ejected from a volcano during a violent eruption. As the ejected material undergoes very rapid cooling and depressurization, some of the trapped gas escape, leaving holes and gas bubbles on the solidified material.

How Are Sedimentary Rocks Formed?

Sedimentary rocks start forming when soil and other materials on the Earth's surface are eroded and finally settle down, forming one layer of sediments. As time passes, more and more materials get eroded and settle on the older layers. Thus, layer upon layer is formed. The lower layers undergo intense pressure due to the weight of the upper layers, eventually evolving into rocks.

Some examples of sedimentary rocks are sandstone, limestone, shale, conglomerate, and gypsum. Sandstone, for instance, is a result of depositions of sand from beaches and rivers. You can find them mostly in deltas, since this is where the rivers flow into the ocean.

How Are Metamorphic Rocks Formed?

To metamorphose or simply to morph means 'to change in form'. Metamorphic rocks are actually products of rocks that have undergone changes. Thus, a metamorphic rock may have originally been an igneous, sedimentary, or even another metamorphic rock. The changes occur when the original rocks are subjected to extreme heat and pressure beneath the Earth's surface.

They may also occur when the the original rocks are caught in the middle of two colliding tectonic boundaries. Some examples of metamorphic rocks are marble, slate, schist and gneiss. Marble, for instance is the result of the metamorphism of limestone and dolostone. When limestone metamorphoses, its calcite grains grow and interlock with one another. As such, marble is denser and harder compared to limestone.

We've written many articles about rocks here in Universe Today. For example, here's Igneous Rocks: How Are They Formed?, What Are The Earth's Layers?, What is the Earth's Mantle Made Of?, After 40 Years Moon Rocks Still Revealing Secrets, Two New Kinds of Moon Rocks Found, Rocks From Mars.

For more information on Moon Rocks, check out NASA's Earth Observatory.

Astronomy Cast also has some interesting episodes on the subject. Here's Episode 113: The Moon - Part I and Questions Show: Shooting Lasers at the Moon and Losing Contact with Rovers

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As a terrestrial planet, Earth is divided into layers based on their chemical and rheological properties. And whereas its interior region - the inner and outer core - are mostly made up of iron and nickel, the mantle and crust are largely composed of silicate rock.