Rocks and Minerals, Weathering, and Soil Third Grade

Rocks and Minerals

Rock is a solid material found in nature. A rock is made up of one or more minerals. For example, some rocks contain quartz. Quartz is a kind of mineral. A mineral is a natural material that was never alive.

Getting the Idea Dig down anywhere on Earth. If you dig far enough, you will come to rock. You can also find rock in many places on Earth’s surface. But rocks are not all the same. Rocks are made of different materials. Different kinds of rocks are found in different places.

What’s the Difference? Look closely at the different kinds of rock shown here. What are some ways that these rocks look different? Basalt Granite Sandstone Gneiss

Rocks and Minerals Certain minerals make up each kind of rock. For example, feldspar and quartz make up most of the rock called granite. The chart shows the main minerals in the rocks from the previous slide. Minerals that Make Up Rocks Kind of RockMain Minerals BasaltPlagioclase, pyroxene GraniteFeldspar, quartz SandstoneCalcite, feldspar, pyrite, quartz GneissFeldspar, quartz

Describing Rocks and Minerals You can see that different kinds of rock have different colors. The colors come from the minerals in the rock. Granite can be pink, yellow, or other colors. The colors come from a mineral called feldspar. You also can see sparkles in granite. The sparkles are bits of quartz. Feldspar

Rocks are different from each other in hardness. Granite is very hard. You cannot scratch it with a nail. Sandstone is softer. A nail will scratch it. Different kinds of minerals are also different in hardness. Minerals are easier to test for hardness that rocks are. This is because minerals are made up of only one material. You can use scratch tests to help identify rocks and minerals.

Often you can see or feel the tiny pieces of minerals in rocks. These pieces are called grains. A rock’s texture is the size and shape of its grains. You can feel texture. Basalt has very small grains. Its texture is fine, or smooth. Granite and gneiss have large grains. Their texture is coarse, or rough. A smooth tire and a rough tire

Measuring Rocks and Minerals Rocks and minerals can be measured and compared. Rocks have different shapes and sizes. Measurements help describe sizes and shapes. You can use a ruler to find how long or wide a rock sample is. Many rocks are round, or shaped like a ball. You can use a tape measure to find the distance around these rocks.

A tool called a pan balance measures mass. Mass is how much matter is in an object. The greater the mass, the more the object weighs. To find the mass of a rock,. Place the rock on one pan. Add weights to the other pan until the scale balances. The total mass of the weights is the mass of the rock. Mass is measured in units called grams (g). pan balance

The volume of an object is how much space is takes up. You can use a tool called a graduated cylinder to measure a rock’s volume. Put a little water in a graduated cylinder. Observe and record the level of water. This is the volume of the water. Then, put the rock in the cylinder. Observe and record the new level of the water. This is the volume of the water and rock together. Subtract the volume of the rock. Volume is measured in milliliters (mL).

Example 27 mL mL ________ 7 mL So, the rock has a volume of 7 milliliters

Discussion Question Suppose you find two rocks. You want to describe how they are alike and different. What are three qualities you could use to describe and compare the rocks?

Lesson Review Question 1.What are rocks made of? A.soil B.water C.minerals D.living things

Lesson Review Question 2.Which sentence is true? A.A mineral was once a living thing. B.Metals are used to make minerals. C.Minerals are found in nature. D.Rocks make up minerals.

Lesson Review Question 3.What is the texture of a rock? A.its color B.the kinds of minerals it contains C.its hardness D.the size and shape of its grains

Lesson Review Question 4.What is the volume of the rock? A.0 mL B.10 mL C.20 mL D.30 mL

Answers 1. C. minerals 2. C. Minerals are found in nature. 3. D. the size and shape of its grains 4. B. 10 mL 30 mL – 20 mL = 10 mL

Weathering

Getting the Idea Rocks can be almost any size. They can be as large as the face of Georgia’s Stone Mountain, or smaller than a grain of sand at the beach. Wind, water, and living things break down larger pieces of rock into smaller pieces. This process is called weathering. Weathering usually takes a long time to happen.

Weathering Water weathers rock from the outside and from the inside. Rivers and streams wear away the rock that surrounds them. Waves at the shoreline break down rocks and cliffs. Moving water also carries away sand, soil, and smaller rocks. These pieces wear away more rock and speed up weathering.

The rocks in this river are being weathered by the moving water.

Weathering works more quickly on “soft” rocks such as sandstone. Sometimes, rivers form canyons. Providence Canyon is in western Georgia. It is 150 feet deep. The Grand Canyon in Arizona is a mile deep! In these areas, moving water and wind have worn away a lot of rock.

The Grand Canyon Providence Canyon These canyons were formed by the weathering of wind and water.

Another kind of weathering happens when water fills in cracks in rocks. When it gets cold enough, the water freezes and forms ice. Water expands, or takes up more space, when it freezes. Each time, the crack gets bigger. The rock can split apart if this happen enough times. This kind of weathering can happen rather quickly.

This diagram shows weathering by ice.

Did you know? Living things also loosen rocks. The roots of trees and other plants grow into cracks in rocks. As the roots grow, they push on the rock, the same way ice does. These plants are growing in the cracks of these rocks.

Weathering by Wind In many areas, wind blows sand against larger rocks. This happens in places such as deserts and seashores. Over time, the blown sand wears some of the rock away. Wind changes the rocks’ shapes. Some rocks may look like arches. Others may look like tall columns.

A rock that has been weathered by wind.

Discussion Questions 1.How is weathering by wind like weathering by water? 2.How is the wind’s action different from that of water?

Lesson Review Question 1.Which of these does NOT weather rock? A.moving water B.minerals C.blowing sand D.ice

Lesson Review Question 2.Weathering changes rocks’ A.size and color. B.color and texture. C.size and shape. D.size and texture.

Lesson Review Question 3.Which action would probably take the longest to weather a hard rock? A.wind blowing sand against the rock B.a river flowing over the rock C.ice freezing in cracks in the rock D.trees growing in cracks of the rock

Lesson Review Question 4.Which statement about weathering is TRUE? A.All rocks weather at the same rate. B.Harder rocks cannot be weathered at all. C.Harder rock weathers faster than softer rock. D.Softer rock weathers faster than harder rock.

Answers 1. B. minerals 2. C. size and shape. 3. A. wind blowing sand against the rock 4. D. Softer rock weathers faster than harder rock.

Soil

Getting the Idea The top part of Earth’s land is mostly covered with a material called soil. Soil is made up of rocks, minerals, and the remains of living things. Living things need soil. Plants grow in it. Many insects, worms, and other animals live in it. Soil is more than just dirt!

Materials in Soil Look closely at a handful of soil. You will see tiny pieces of rock. In Lesson 2, you learned how weathering breaks rock down into smaller pieces. Very tiny pieces of rock, called particles, are the main material in soil.

Soil also contains the remains of dead plants and animals. Over time, the dead plants and animals break down into small bits. These bits make up a dark-colored material called humus. Humus helps soil hold water. Humus also contains nutrients. A nutrient is something that a plant or animal needs to live and grow. Earthworms and other animals add nutrients to soil, too. The nutrients are in the wastes that come out of the animals’ bodies. Humus

Soil also contains minerals and water. The amount of water soil can hold depends on the kind of soil. Did you know?

Kinds of Soil: Sand Sand has the largest particles. Sand contains the mineral quartz. Sand on beaches may also have tiny pieces of broken shells init. Sand has different colors because it comes from different- colored rocks. If you run your fingers through sand, it feels rough. Sand has large air spaces between the particles. Water flows easily through the spaces, so sand does not hold water well. Sand

Kinds of Soil: Silt The particles of silt are smaller than those in sand. Silt feels more smooth when you touch it. Silt holds water better than sand does. Rivers carry silt from one place to another. When a river floods the land, the water leaves silt behind. Silt

Kinds of Soil: Clay Clay is the kind of soil with the smallest particles. If you squeeze some clay in your hand, it feels sticky and smooth. Clay can be different colors, but most clay looks reddish or brown. The spaces between the particles of clay are tiny. Clay holds water very well. But it is hard for plant roots to frown down into clay to take up the water. Dried, red clay

Did you know? Clay is made up of tiny particles of weathered rock. People can use clay to make lots of different things. First, people have to mine the clay, or get it out of the ground. Georgia mines more clay than any other state.

Kinds of Soil: Loam Many soils are a mixture of sand, silt, and clay. These soils are called loam. Loam feels crumbly. Most kinds of plants grow best in loam. It holds water well. Plant roots grow down easily in loam. Potting soil sold in bags is loam. Loam

Loam The chart shows just one possible mixture of loam. Soils are different from place to place. In one place, the soil may be mostly clay or mostly silt. Different kinds of plants grow in different kinds of soil.

Layers of Soil The soil that covers Earth’s land has different layers. The top layer is called topsoil. This is the layer of soil in which most plants grow. Topsoil has lots of humus in it. Insects, worms, and other animals make their homes in topsoil.

The next layer is subsoil. Subsoil is mostly rock particles, with very little humus. Roots of trees grow down into subsoil. Under the subsoil is a layer of larger pieces of weathered rock. The rock is broken up, but the pieces are bigger than soil particles. Under the weathered rock is solid rock, called bedrock. The picture below shows the layers of soil on top of bedrock.

Diagram of the Layers of Soil

Discussion Questions 1.How are the different kinds of soil alike? 2.How are they different?

Lesson Review Question 1.A student wants to grow a plant in a pot. Which kind of soil will be BEST to use? A.sand B.silt C.clay D.loam

Lesson Review Question 2.What is the main material in soil? A.humus B.rock particles C.nutrients D.living things

Lesson Review Question 3.Where would you find the MOST plant roots and animals? A.in topsoil B.in humus C.in bedrock D.in subsoil

Lesson Review Question 1.Which kind of soil has the largest particles? A.sand B.silt C.clay D.loam

Answers 1. D. loam 2. B. rock particles 3. A. in topsoil 4. A. sand