11What can Break a Boulder? When you think of rocks, words likehard and solid may come to mind.You may think rocks can’t even break,but that’s not true. Rocks can becracked and crushed by merewind and rain.
20Living things can also cause weathering Living things can also cause weathering. A tree’s roots can grow in a small crack in a rock. As the roots grow, it can push the rock apart until the rock breaks.
21Animals may dig up rocks, causing the rocks to be exposed to wind and rain.
22Chemicals in water and rain that flow through and around rocks can also cause weathering. These chemicals can combine with the rock and change it so that it crumbles and wears away.
25Don’t rocks just sit around Rocks on the MoveDon’t rocks just sit aroundin the sun all day?No. Rocks can move!
26Weathering is the beginning of a series of changes that often occurs to rocks on Earth’s surface. The same wind and water that can cause weathering also can carry the broken bits of rock away. The process of moving weathered rock from one place to another is called erosion.
27The erosion of rock can be caused by many different natural processes The erosion of rock can be caused by many different natural processes. Moving water is one of the most common causes of erosion.
28The fast-moving water in this stream can shift or move large rocks near the top of the mountain. Together with gravity, water can cause the rocks to move downhill.
30The water pulls the larger pieces of weathered rock along the river’s bottom. As the water slows down, it has less energy. It cannot move the largest rocks and pebbles anymore. These are left behind as the water moves on. The dropping of weathered rock by wind or moving water is known as deposition.
31As the water in a river continues to slow down, more bits of weathered rock are dropped and left behind. This happens because slow-moving water can only carry very small pieces of rock, such as sand and silt. These bits of rock are called sediment.
32When rivers reach the ocean, they slow down even more When rivers reach the ocean, they slow down even more. As they slow down, much of the remaining sediment in the water is dropped. Over time, the sediment piles up near the mouth of the river. It forms a landform called a delta.
34The wind is just moving air, so what can it do? Wind blows sand and other sediment away.
35Wind can carry away soil and other sediment. Where does all of it go Wind can carry away soil and other sediment. Where does all of it go? Some particles are not carried very far. Others can be carried thousands of miles away. Sand from the Sahara Desert, in Africa, is sometimes carried all the way across the Atlantic Ocean to the United States.
36Wind may deposit a lot of sand in one area Wind may deposit a lot of sand in one area. Over time the sand builds up and forms dunes. Sand dunes are often found near sandy beaches.
38This rock, called a mushroom rock, began as a giant boulder This rock, called a mushroom rock, began as a giant boulder. Wind slowly eroded the rock, leaving the mushroom shape behind.
39Huge sheets of ice are called glaciers. Can you imagine an ice cube the size of a city? Some chunks of ice are even larger than that!Huge sheets of ice are called glaciers.
40Glaciers are found in very cold places Glaciers are found in very cold places. You may think that because a glacier is made of ice, it does not move. But the ice flows like a very slow river. As the glacier flows, it picks up large rocks and boulders.
42Glaciers pick up rocks and the soil under it, causing erosion Glaciers pick up rocks and the soil under it, causing erosion. When the glacier begins to melt, the rocks and sediment drop out of the ice. This sediment forms many different features, including hills called moraines.
46Just as gravity causes a ball to fall back to earth, it causes rocks and sediment to slide down mountains and cliffs. Gravity can even cause huge chunks of rock and soil to slide down a slope all at once. This is called a landslide.
49Landslides happen a lot in mountain ranges Landslides happen a lot in mountain ranges. A hill’s slope affects how gravity will act on it. If the slope is steep, rocks are much more likely to fall than if it is not steep.
50Do the Math Measure Angles The steepness of a slope is measured in degrees. Use a protractor to measure the three slopes. Which has the steepest slope?
51WATERWater carries dirt down the drain when you wash your hands. It also carries rocks and sediment down a river or along a beach.
52Flowing water has energy. That energy can carry sediment down a river Flowing water has energy. That energy can carry sediment down a river. Ocean waves have a lot of energy. Waves crash on rocks along a shore, causing rocks to break apart. The waves cut cliffs and cause caves to form. Waves can also carry away sediment and deposit it in other places. Over time a beach may form or a beach can be washed away.
55desposition erosion glacier gravity landform sediment weathering Check What You KnowWhat process causes rocks to break down into smaller pieces?What process causes eroded sediments to be dropped off in another place?What is a land feature such as a delta or a sand dune called?What are broken-down pieces of rock called?What process carries away weathered rock?What is a large sheet of flowing ice called?What force causes landslides to occur?desposition erosion glacier gravity landform sediment weathering
56What Are Minerals? Mission: Identify the physical properties of common earth-forming minerals,including hardness, color, luster, andstreak color, and recognize the roleof minerals in the formation of rocks.
57What do copper, table salt, and diamonds have in common? They are all minerals!
58A mineral is any nonliving solid that has a crystal form. All minerals form in nature –under the ground, in caves,and even in the air.There are over 4,700 differentminerals found on Earth.
59When you think of crystals, you may think of ones like those in caves. Butnot all crystals look like those. Mineralcrystals come in different shapes, butthere is something that is the same.The particles in a crystal combine toform a shape that is repeated over andover again. It is this repeated structurethat defines a crystal.
60Minerals are the same in another way, too Minerals are the same in another way, too. Each mineral is made up of the same set of nonliving things called elements. For example, the mineral calcite is always made of the elements calcium, carbon, and oxygen.
61Rubies are always made of aluminum and oxygen. Diamonds are always made of carbon.
62One characteristic that can help you identify minerals is crystal shape. SQUARE SQUARE HEXAGONALPYRAMID PRISM PRISMBERYLPYRITEFLUORITE
63Which Mineral Is Which?With more than 4,700 minerals in the world, how can you tell one mineral from another?
64HARDNESS is one property used to identify minerals HARDNESS is one property used to identify minerals. Hardness is a mineral’s ability to scratch another mineral. In a scientist named Friedrich Mohs developed a scale to compare the hardness of different minerals.
65The softest minerals score a 1. On the Moh’s scale, a mineral with a higher number can scratch a mineral with a lower or equal number.The softest minerals score a 1.Every other mineral can scratch minerals with a hardness of 1.The hardest mineral is a diamond. It scores a 10 on the Moh’s scale.Only another diamond can scratch a diamond.
67Another property used to tell one mineral from another is LUSTER. Luster describes how minerals reflect light. The minerals copper, gold, and silver each have a metallic luster.Talc and gypsum each have an earthy luster.
68Suppose you found this bright purple mineral Suppose you found this bright purple mineral. How would you describe its luster?
69This mineral can be scratched by diamond but not by feldspar This mineral can be scratched by diamond but not by feldspar. What would the mineral’s hardness be?
74You can use all sorts of properties to identify minerals You can use all sorts of properties to identify minerals. Some are more useful than others. But if you use all of them, you’ll probably be able to identify the mineral every time!
75The color of a mineral may vary, but its streak is always the same. To identify a mineral you can rub the mineral against a white tile called a streak plate. The color left behind is called the mineral’s streak.
76Pyrite has a gold color, but its streak is greenish-black. Sometimes a streak is the same color as the mineral itself. But this is not true for all minerals.Pyrite has a gold color, but its streak is greenish-black.
77Magnetite attracts things that have iron in them. Magnetism is another propertyyou can test for.
78You have learned that mineral crystals come in different shapes You have learned that mineral crystals come in different shapes. Mineral crystals also break in a certain way. The way a mineral breaks is another way you can use to identify it. When some minerals break, the broken sides are smooth and straight. Minerals that break this way have cleavage. Minerals that do not break along smooth lines have fracture.
79This piece of mica has cleavage. It breaks into thin, flat sheets.
80A mineral can come in different colors A mineral can come in different colors. Corundum crystals can be red, blue, green, yellow, purple, or brown. Yet no matter what color the corundum crystal is, its streak is always white. Because of this streak color is useful when identifying a mineral.
81Some minerals have other properties. Calcite and fluorite glow under a black light. Calcite also fizzes when you put a drop of vinegar on it.Quartz can conduct electricity.calcitefluorite
82What tests could you use? Look at the minerals shown here. They are all quartz. How could you show that they are all quartz?What tests could you use?
83cleavage crystal hardness luster minerals streak Show What You Knowcleavage crystal hardness luster minerals streak1. You can find out a minerals’ _______ by seeing what other minerals it can scratch.2. A nonliving solid that has a _______ form is called a mineral.3. Gold, silver, copper, and pyrite each have a metallic _______.4. Fluorite, talc, diamond, gold, and quartz are all examples of _______.5. The color left behind when a mineral is rubbed across a white tile is its _______.6. A mineral that breaks along straight, smooth lines is said to have _______.
84Think! This mineral can scratch talc, but not calcite. ____ This mineral can scratch apatite, but not quartz. ____12345678910talcgypsumcalciteFluoriteapatitefeldsparquartztopazcorundumdiamond
85How Can Rocks Be Classified? Identify the three categories of rocks:igneous, sedimentary, and metamorphic.