WHAT WILL YOU LEARN 1. What the three types of rocks are. 2. How one type of rock can change into another. 3. How common each rock type is in Earth's crust.
A rock is a naturally formed solid that is usually made up of one or more types of minerals.
A few types of rocks are made up of one kind of mineral, and a few contain no minerals at all. Limestone, for example, can be composed entirely of the mineral calcite. Obsidian (ahb-SIHD-ee-uhn) is a rock that contains no minerals. It consists of natural glass, which is not a mineral because it does not have a crystal structure.
Earth is built almost entirely of rock. These surface features, however, form only a very thin covering on the planet. Between this thin layer and Earth's metallic core, Earth is made of solid and molten rock.
The building of houses and skyscrapers The sources of metals, such as iron, aluminum, and copper The carving of statues and other works of art As a base for pavement for roads and highways
People study rocks to learn how areas have changed through time. Rocks show that North America, as well as most of the rest of the world, has been buried under thick layers of ice many times.
The rock cycle is the set of natural processes that form, change, break down, and re-form rocks. Rocks do change. But the changes usually occur over a huge span of time–thousands to millions of years. A cycle is made up of repeating events that happen one after another. This does not mean that rocks move through the rock cycle in a particular order.
A rock at any point in the cycle can change in two or three different ways. Like all cycles, the rock cycle has no beginning or ending but goes on continually. The next slide explains how the rock cycle works!!!!
The three types of rocks are classified by how they form. 1. IGNEOUS ROCK 2. SEDIMENTARY ROCK 3. METAMORPHIC ROCK
Created when molten rock (magma) inside the Earth pushes through the crust (like in volcanic eruption) and then cools and recrystallizes into a solid. Igneous rock can form within Earth, or it can form on Earth's surface where volcanoes have or do exist. Igneous rocks that originally formed at great depths can reach Earth's surface over time. Deep rocks may be raised closer to the surface when mountains are pushed up.
Loose material is carried by water or wind and then settles out, forming layers. Formed where oceans or bodies of water once existed or do exist. Forms when pieces of older rocks, plants, and other loose material get pressed or cemented together. The lower layers of material can get pressed into rock by the weight of the upper layers.
Forms when heat or pressure causes older rocks to change into new types of rocks. Formed deep within the earth (where pressure and heat have very large affect) Formed during mountain building when igneous or sedimentary rocks are buried deep in the earth. These conditions cause the structure of the rock to change and new minerals to grow in place of the original minerals.
Igneous, sedimentary, and metamorphic rocks are all found in Earth's crust. But these rock types are not evenly distributed. Most of Earth's crust–95 percent of it–consists of igneous rock and metamorphic rock. Sedimentary rock, which forms a thin covering on Earth's surface, makes up only 5 percent of the crust.
The distribution of rock types is a reflection of the rock cycle. Sedimentary rocks are most common at the surface because they are formed by processes that occur at the surface. Most igneous rocks and metamorphic rocks are formed by processes that occur deeper within Earth.
Magma and lava form different types of igneous rocks. Igneous rocks form from molten rock, but where does molten rock come from? Deep within Earth! Molten rock is called magma. Molten rock that reaches Earth's surface is called lava.
An igneous rock is classified on the basis of its mineral composition and the size of its mineral crystals. A rock formed from magma can have the same composition as a rock formed from lava. The rocks, though, will have different names, because the sizes of their crystals will be very different. You will read why later in this section.
Depending on where they form, igneous rocks are classified as intrusive or extrusive. An intrusive igneous rock is one that forms when magma cools within Earth. An extrusive igneous rock is one that forms when lava cools on Earth's surface.
You can see extrusive igneous rocks at Earth's surface. But intrusive igneous rocks form within Earth. So how do they reach the surface?
Forces inside Earth can push rocks up, as when mountains form. Also, water and wind break apart and carry away surface rocks. Then deeper rocks are uncovered at the surface.
The texture of an igneous rock–that is, the size of its mineral crystals– depends on how quickly magma or lava cooled to form it.
The magma that forms intrusive igneous rocks stays below the surface of Earth. Large crystals can form in intrusive rocks because: The interior of Earth is very hot The high temperatures allow magma to cool slowly Slow cooling allows time for large mineral crystals to form
The lava that forms extrusive igneous rocks reaches Earth's surface. Very small crystals form in extrusive rocks because The surface of Earth is cooler than Earth's interior The lower temperatures cause the lava to cool quickly There is no time for large mineral crystals to form
Some igneous rocks contain crystals of very different sizes. These rocks formed from magma that started cooling within Earth and then erupted onto the surface. The large crystals grew as the magma cooled slowly. The small crystals grew as the lava cooled quickly.
#2 is Granite #5 is Gabbro #8 is Basalt #9 is Rhyolite # 10 is Andesite #12 is Obsidian # 14 is Pumice#15 is Scoria
Texture is not enough to identify an igneous rock. Think about substances that have similar textures, such as sugar and salt. A spoonful of sugar and a spoonful of salt both consist of small white grains. However, sugar and salt are different materials–that is, they have different compositions.
Different igneous rocks might also have similar textures. To identify them, you must also consider their compositions. Most igneous rocks are mainly made up of silicate minerals, which you read about in the last chapter.
The silicate mineral group is the most common group in Earth's crust. Silicate minerals contain varying amounts of silica, a compound of silicon and oxygen. After identifying the texture of an igneous rock, geologists classify the rock on the basis of how rich it is in silica.
Special equipment must be used to determine a rock's exact composition, but you can estimate the level of silica in an igneous rock by looking at its color. Igneous rocks with high levels of silica, such as granite and rhyolite, are typically light in color. Those with low levels of silica, such as gabbro and basalt, are dark in color.
Intrusive Rock Formations In northwestern New Mexico, a great peak rises out of a flat, barren desert. In English, it’s called Ship Rock, because it looks something like a sailing ship. Ship Rock is an example of the kinds of landforms that are made of igneous rocks. A landform is a natural feature on Earth’s land surface.
As magma pushes up toward Earth’s surface, it makes channels and other formations underground. Formations of intrusive igneous rock can be harder and more lasting than other types of rock. Igneous rock tends to be harder than sedimentary rock.
# 5 Explain how sedimentary rocks form and distinguish between the different types of sedimentary rocks based on the makeup of rocks. What are the processes that form sedimentary rocks? How do sedimentary rocks record past conditions?
Sedimentary rock takes its name from the word sediment, which means “something that settles.” Sediments are materials that settle out of water or air. Sedimentary rocks develop from layers of sediments that build up on land or underwater. They are the most common rock type on the surface of the earth.
Weathering-All rocks are subject to weathering. Weathering is anything that breaks the rocks into smaller pieces or sediments. This can happen by the forces like wind, rain, and freezing water. Deposition-The sediments that form from these actions are often carried to other places by the wind, running water, and gravity. As these forces lose energy the sediments settle out of the air or water. THE STARTING POINT
Just as water washes mud off your hands as it runs over them, rainwater washes away rock particles as it flows downhill. The water carries these rock particles to streams and rivers, which eventually empty into lakes or oceans. Strong winds also pick up sand and rock dust and carry them.
As winds or water currents slow down, rock particles settle on the land or at the bottom of rivers, lakes, and oceans. This is called deposition. The sediments form layers as larger particles settle first, followed by smaller ones.
CLASTIC- Formed from rock particles (fragments of preexisting rock ), pressure and dissolved minerals that recrystallize!!!! CHEMICAL- Formed from the recrystallization of dissolved minerals in water!!!! (liquid to solid) ORGANIC- Rock composed mostly of the remains of plants and animals!!!!!!
Sedimentary rock is a type of rock that is formed by sedimentation of material at the Earth's surface and within bodies of water. It also forms from dissolved minerals and the remains of dead plants and animals.
Rocks and mineral pieces are called clasts. When these, clasts build up in layers, and cement together, clastic sedimentary rock is formed. Rock particles settle out of wind and water according to size. The weight of the top puts pressure on the buried sediments. This pressure may be enough to press the loose rock particles together or they may be “glued” together when dissolved minerals recrystalize. Conglomerate is an example of sedimentary rock formed from loose rock particles.
When sand on a beach becomes cemented together, they form a sedimentary rock called sandstone. Most sedimentary rock forms from loose material that gets pressed together or cemented into rock. But their are other ways too.
You will use the following slide to recreate how sedimentary rock forms from particles. As you draw think about why each particle forms where it does. How does sedimentary rock form from particles?
Chemical sedimentary rocks differ from other sedimentary rocks because they are decomposed at the surface of the earth. These sedimentary rocks are formed as dissolved minerals in water become solid again. Water is able to dissolve some minerals. When the water evaporates it leaves the minerals behind. Over time, these minerals build up to form chemical sedimentary rock. Limestone is a chemical sedimentary rock if it contains no sea shells only calcium carbonate (calcite) mixed with clay sand and silt.
The water in oceans, lakes, rivers, and streams contains minerals that came from rocks. Some of these minerals are in solid form. Some of these minerals dissolve and are carried along with it.
Water often flows through cracks in rock that is near Earth's surface. As water moves through limestone, some of the rock dissolves. A large open space, or cave, can be left in the rock. As the water flows and drips through the cave, some of it evaporates. The new limestone that forms can take many odd and beautiful shapes.
Sometimes minerals crystallize along the edges of lakes and oceans where the climate is dry and a lot of water evaporates quickly. Over time, the minerals build up and form layers of sedimentary rock. Rock salt and gypsum form in this way.
Some rocks form from plants or shells. These remains are fossils. A fossil is the remains or trace of an organism from long ago. Coal is an unusual sedimentary rock because it forms from plants instead of earlier rocks. Coal is a fossil fuel because it is made from the remains of ancient plants. The coal people use today started forming millions of years ago in swamps. As plants died, their remains fell upon the remains of earlier plants.
Processes similar to the ones that produce sedimentary rocks from rock particles also produce rocks from shells or plant remains. These remains are fossils. A fossil is the remains or trace of an organism from long ago.
Limestone is made up of carbonate minerals, such as calcite. The shells and skeletons of ocean organisms are formed of these minerals. When the organisms die, the shells and skeletons settle on the ocean floor as layers of sediment.
Over time, the layers become buried, pressed together, and cemented to form Organic limestone. The photographs on the next slide show how loose shells can become limestone.
Coral reefs also consist of limestone that comes from organisms. However, in the case of reefs, the limestone is produced directly as coral organisms build their skeletons one on top of another. In the formation of coral, the rock does not go through a loose-sediment stage.
#6 I can explain how metamorphic rocks form from other rocks and distinguish between foliated and non- foliated metamorphic rocks.
How does a rock change into another kind of rock? Examine a sample of shale and a sample of schist (shihst). Shale, a sedimentary rock, can change into schist. Think about how this change could occur without the shale's melting or breaking apart. Make a prediction about what process changes shale into schist.
Metamorphic rocks form as existing rocks change. Heat and pressure change existing rocks into metamorphic rock. The process in which an existing rock is changed by heat or pressure—or both—is called metamorphism. The original sedimentary or igneous rock is called the parent rock. So any type of rock can be a metamorphic rocks parent rock!
During metamorphism, rocks undergo many changes. One type of change occurs when pressure causes a rock's minerals to flatten out in one direction. Other changes can occur in a rock's minerals, but the rock remains solid. Rocks do not melt when they undergo metamorphism.
Heat and pressure can break the bonds that join atoms in minerals. Then the atoms can join together differently as new bonds form. This process is called recrystallization. It has two main results. First, individual mineral crystals can grow larger as more atoms join their crystal structures. Second, atoms can combine in different ways, and new minerals can form in place of older ones.
Most metamorphic rocks develop bands of minerals. Foliation is an arrangement of minerals in flat or wavy parallel bands. Foliated rocks either split easily into leaf like sheets or have bands of minerals that are lined up and easy to see.
Foliation develops when rocks are under pressure. Foliation is common in rocks produced by metamorphic changes that affect large areas. Metamorphic rocks that do not show foliation are called nonfoliated rocks.
One common nonfoliated metamorphic rock is marble, which develops from limestone. Marble is used as a decorative stone. It is good for carving and sculpting. Because marble is nonfoliated, it does not split into layers as an artist is working with it.
The types of metamorphic changes that occur depend on the types of parent rocks and the conditions of temperature and pressure. When both high temperature and high pressure are present, metamorphic changes can occur over very large areas.
When only one of these conditions is present, changes tend to occur over smaller areas.
Most metamorphic changes occur over large areas in which both temperature and pressure are high. An example is a region where large blocks of rock are pressing together and pushing up mountain ranges.
In such an area, rocks are buried, pressed together, bent, and heated. The pressure and heat cause the rocks to undergo metamorphism. Generally, the deeper below the surface the rocks are, the greater the metamorphic changes that occur in them.
Some metamorphic changes occur over small areas. For example, magma can push into rocks underground, or surface rock can be covered by a lava flow. The magma or lava heats the rock it is in contact with, causing recrystallization.
These changes are mainly due to high temperature, not pressure. The rocks get roasted but not squeezed.
The rock cycle is the set of natural processes that form, change, break down, and re-form rocks. Rocks do not move through the rock cycle in a particular order.
Rocks can change in many ways. Using sedimentary, metamorphic, and igneous rocks as examples, explain how igneous rock might change into sedimentary rock. Then explain how metamorphic rock might change into igneous rock.