Chapter 4- rocks

The Rock Cycle H.W. pg. 93 ques. 1-4 A rock is a mixture of minerals, rock fragments, volcanic glass, organic matter, and other natural materials. All rocks slowly change through time, and the model that we use to show this slow change is called the rock cycle .

Discovery of the Rock Cycle James Hutton recognized that rocks undergo changes in 1788.

Rock Cycle As you can see the rock cycle shows 3 different types of rock: Sedimentary Metamorphic Igneous Also you see that all 3 types can be formed in a number of ways. This shows that any rock can change into any of the three major rock types.

Rock Cycle Within the rock cycle rocks can be weathered to small rock and mineral grains. These grains could then be carried away by wind, water, or ice. This is what we call erosion . This does not mean that the minerals and chemical elements that make up rock are destroyed. The elements that make up rocks are not destroyed they are just redistributed in other forms.

Igneous Rock Section 4-2 H.W. pg. 97 questions 1-4 Igneous rock forms when magma cools and hardens. At certain within the Earth, the temperature and pressure are just right for rocks to melt and form magma. Magma can be located at depths of 150km below the Earths surface. The temperature of this magma can range between 650- 1,200 o C, depending on their chemical compositions and pressures exerted on them.

Igneous Rock The reason that these rocks melt is because of heat that is formed in the Earth’s interior. The heat comes from the decay of radioactive material inside the Earth. Another source of this heat is actually heat that is left over from the formation of the planet, which was originally molten. Since magma is less dense than the surrounding rocks it is forced upward toward the surface, like in a volcano. When magma reaches the Earths surface and flows from volcanoes it is then called lava

Igneous Rock So magma is melted rock material composed of common elements and fluids. As magma cools atoms and compounds rearrange themselves into new crystals called mineral grains . And rocks form as these mineral grains grow together. So rocks that form from magma below the Earths surface are called intrusive. These intrusive rocks stay underground until the land above them are removed, either by erosion of by physical means, and exposed to the surface.

Igneous Rock Intrusive rocks form at deep depths of the Earth. This causes the rocks to cool very slowly. Slowly cooled magma will then produce very large mineral grains that we can see, within the intrusive rocks.

Igneous Rock Extrusive igneous rocks are formed by the cooling of lava on the surface of the Earth. When lava cools on the surface it could be exposed to water and air. This causes the lava to cool quickly and does not allow large mineral grains to form. Therefore extrusive igneous rock looks fine grained.

Classifying Igneous Rock Besides intrusive and extrusively forming. The type of igneous rock also depends on the magma from which it forms. An igneous rock can form from basaltic, andesitic, or granitic, magma. The type of magma that rocks form from determines important chemical and physical properties of that rock. These include mineral composition, density, color, and melting point.

Basaltic Rock These are dense dark colored igneous rock that form from magma that is rich in magnesium and iron, and lack in silica. The iron and magnesium give these rocks the dark color. This basaltic magma flows, largely from the mountains in Hawaii, which explains the black color of Hawaii’s beaches.

Granitic Rock These are light colored igneous rock that have a lower density than basaltic rocks. Granitic magma has more silica and less iron and magnesium then basaltic magma

Andesitic Rock This type of magma has a chemical composition that is between basaltic and granitic rock, when dealing with silica, magnesium and iron. It has more iron and magnesium than granitic and less silica than granitic. Usually found in volcanoes along the Pacific Coast.

Metamorphic Rock Section 4-3 H.W. pg 102 ques. 1-4 Rocks that have changed because of changes in temperature and pressure or the presence of hot, watery fluids are called Metamorphic Rock. These changes can be in the form of the rock or in its composition or both. Metamorphic rocks can form from igneous, sedimentary or from other metamorphic rocks. Ex: When you add heat and pressure to granite, the mineral grains are flattened and a metamorphic rock called gneiss is formed.

How heat and Pressure effect rocks. Rocks beneath the Earth’s surface are under great pressure from the rock layers above them. Also, temperature increases as the depth of the Earth increases. In some areas under the Earth’s surface the Temp and pressure is just right to allow rock to melt and magma to form. In other areas, melting doesn’t occur but some mineral grains change by dissolving and recrystallizing, in the presence of liquids.

How heat and Pressure effect rocks. Depending on the amount of pressure and temperature applied, one type of rock can change into several different metamorphic rocks, and every metamorphic rock can come from several different parent rocks. Ex: The sedamentary rock shale will change into slate. As you increase pressure slate turns into phyllite, then schist and then eventually gneiss.

How heat and Pressure effect rocks.

How heat and Pressure effect rocks. Lastly, schist can also form basalt.

How Hot Fluids Effect Rocks Some fluids can move through rock. These fluids are usually hot and mostly water with dissolved elements, CO 2 and compounds. When these fluids pass through rocks they react chemically with the rock to change its composition. This occurs a lot when rock surrounds a hot magma body and the fluids from the magma react with the surrounding rock.

How to Classify Metamorphic Rock Metamorphic rocks can form from igneous, sedimentary, or other metamorphic rocks through their interaction with heat pressure and hot fluids. We classify these rocks by their composition and texture. First is Foliated rocks . A metamorphic rock is said to have foliated texture when mineral grains in the rock line up in parallel layers.

Metamorphic foliated rock Two examples of foliated rocks are slate and gneiss.

Metamorphic foliated rock Slate forms from a Sedimentary rock called shale. The minerals in shale arrange into layers when they are exposed to heat and pressure. This allows slate to separate easily along these foliation layers. The pressure is so great during this change that the minerals in slate get pressed so tightly that water cannot pass through it, making it virtually water tight. This unique property makes slate the optimal rock for the use of patios and paving around pools.

Metamorphic foliated rock Gneiss, another foliated rock, forms when granite is changed. The foliation in gneiss shows up as alternating light and dark bands. This is because during the transformation from granite to gneiss the light atoms of quartz and feldspar are separated from the darker atoms of mica.

Non Foliated metamorphic Rock In non foliated metamorphic rock layering does not occur. The mineral grains grow and rearrange but do not form layers. This produces a non foliated texture. An example is when sandstone, a sedimentary rock composed of mostly quartz grains, is exposed to heat and pressure. The quartz grains here grow in size and become interlocking like a jigsaw puzzle. The resulting rock is called quartzite.

Non Foliated metamorphic Rock Another example of non foliated metamorphic rock is marble. Marble forms from the sedimentary rock limestone, which is rich with the mineral calcite. Marble that is a different color than white is due to the presence of other minerals besides calcite that is present. Hornblende gives marble a black or greenish color And hematite gives marble a reddish color.

Sedimentary Rock Section 4-4 H.W. Pg 109 ques. 1-5 Igneous rocks are the most common rocks on Earth. However we don’t see them a lot because they are mostly beneath the Earths surface. 75% of the rocks that are exposed at the surface are sedimentary rocks . Sediments are loose materials such as rock fragments, mineral grains, and bits and pieces of shell that have been moved by wind, water, or ice These sediments come from already existing rock that were weathered or eroded. Sedimentary rock forms when these sediments are pressed together by great pressure, or when minerals form in solution.

Stacked Rocks Sedimentary rocks often form in layers. The older layers are on the bottom layers because they were deposited first. Sometimes these layers can be disturbed by the forces of nature. This will sometimes overturn the layered sedimentary rock and the oldest will no longer be on the bottom.

Classifying Sedimentary Rocks The sediments that form sedimentary rocks can be almost anything that is found in nature. Sediments can come from weathered or eroded igneous, metamorphic, sedimentary rocks. And the composition of sedimentary rocks depends on the composition of the sediments that formed that rock. Like the other rocks we spoke of, sedimentary rocks are classified by their composition and are classified as: detrital, chemical, or organic.

Detrital Sedimentary Rock Detrital means “to wear away” in Latin, and are made from broken fragments of other rocks. These broken fragments are compacted together by pressure and cemented together to form solid rock. These broken fragments of rocks can form in a number of ways. One way is by weathering and erosion. When rock is exposed to air, water, or ice it is unstable and breaks down chemically and mechanically. This process, which breaks down rocks into smaller pieces, is called weathering and the actual movement of these smaller pieces is called erosion .

Detrital Sedimentary Rock H.W. pg 114 questions 1-10 Compaction is also a part of sedimentary rock formation. Erosion moves sediments to a new location, where they will be deposited. Now layer upon layer of sediment builds up. Pressure from all of the built up layers pushes down on the lower layers causing the small fragments to form solid rock. This process is called compaction.

Detrital Sedimentary Rock If the fragments are large, like the size of pebbles or sand, pressure alone can’t make the solid rock form. When water moves through soil and rock, it picks up materials released from minerals during weathering. This dissolved mineral solution then moves between the large loose rock sediments and cements them together. Cementation , usually occurs when minerals such as quartz, calcite, and hematite are deposited between sediments. These minerals act as natural cement and hold sediments together like glue, and forming detrital sedimentary rock.

Detrital Sedimentary Rock Detrital rocks have a granular texture, kind of like granulated sugar. And they are named according to the shapes and sizes of the sediments that form them. Ex: The Sedimentary rocks, conglomerate and breccia both form from large sediments. If the sediments are rounded, the rock is called conglomerate. If the sediments are sharp then the rock is called breccia. The roundness of sediment particles depends on how far they have been moved by wind or water.

Materials Found in Sedimentary Rocks H.W. pg 114 ques. 11-20 The gravel sized sediments in conglomerate and breccia are often composed of quartz and feldspar. These 2 minerals (quartz, feldspar) can be found in gneiss, granite, and limestone. The natural cement that holds the sediments in sedimentary rock together are usually quartz and calcite. Sandstone if formed from smaller particles than conglomerate and breccia, but they are made from types of quartz and feldspar that are more resistant to weathering.

Chemical Sedimentary Rock This is the second type of sedimentary rock, and it is formed when dissolved minerals come out of solution. Like our saltwater example, mineral deposits can form sediments and rocks when sea or lake water evaporates. An example of chemical sedimentary rock is gypsum. Chemical sedimentary rocks do not form from pieces of preexisting rocks.

Chemical Sedimentary Rock Limestone- this is composed mostly of Calcium Carbonate CaCO 3 . And forms when calcium carbonate comes out of solution as calcite and its many crystals grow together to form limestone. Limestone is 50% calcite and is usually deposited on the bottom of lakes or shallow seas. A lot of the United States bedrock is made of limestone. And that is due to the fact that seas covered much of the country for millions of years.

Chemical Sedimentary Rock Rock Salt- When water is very rich in dissolved salt , it often deposits the mineral halite. Halite deposits can range in thickness from a few meters to more than 400m. Companies mine these deposits because it is used as a very important resource. Its used in the making of glass, paper, soap, and some dairy products. Also, its processed and used as table salt.

Organic Sedimentary Rock Rocks that are made of the remains of once-living things are called organic sedimentary rocks. The most common of this type of this rock would be fossil rich limestone. The difference between regular limestone and fossil rich limestone is that fossil rich limestone contains some remnant of once living ocean organisms, instead of just calcite. Ex: muscles, clams, coral, snails. They have shells made from calcium carbonate. When these shells cement together they form fossil rich limestone.

Fossil rich limestone If a rock is completely made of shell fragments that you can see, the rock is called coquina.

Organic sedimentary rock Chalk- is another organic sedimentary rock that is made of microscopic shells. When you write with naturally occurring chalk you a crushing and smearing the calcite-shells remains of a once living organism. Coal- is another useful organic sedimentary rock. It forms when dead plants are buried under other sediments in swamps. Microorganisms feed off of and change these plant materials, and they are compacted over millions of years to eventually form coal.

H.W. pg 116 questions 1-17 Test on chapter 3 in one week!!!!!!!!!!!!!

Chapter 4- rocks

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