The energy of sunlight powers our biosphere (air, water, land, and life on the earth’s surface). About 50 percent of the solar energy striking the earth is converted to heat that warms our planet and drives the winds. About 30 percent of the solar energy is reflected directly back into space. The water cycle (evaporation of water followed by rain or snow) is powered by about 20 percent of the solar energy.

Some of the sunlight that reaches the earth is used by plants in photosynthesis. Plants containing chlorophyll use photosynthesis to change sunlight to energy. Since these green plants form the base of the food chain, all plants and animals depend on solar energy for their survival.

When the sun is overhead, about 1,000 watts of solar power strike 1 square meter (10.8 square feet) of the earth’s surface. Using solar cells, this solar energy can be converted to electricity. However, because sunlight cannot be converted completely to electricity, it takes at least a square meter of area to gather enough sunlight to run a 100-watt light bulb.

Solar energy is still more expensive than other methods of generating electricity. However, the cost of solar electricity has greatly decreased since the first solar cells were developed in 1954.

It has been proposed that panels of solar cells on satellites in orbit above the earth could convert solar energy to electricity twenty-four hours a day. These huge solar power satellites could convert electrical energy to microwaves and then beam these microwaves to Earth. At the earth’s surface, tremendous fields covered with antennas could convert the microwave energy back to electricity.

It would take thousands of astronauts many years to build such a complicated system. However, there are many practical uses of solar energy in use today. These uses include heating water, heating and cooling buildings, producing electricity from solar cells, and using rain and snow from the water cycle to power electrical generators at dams.

In the following experiments, you will examine the use of solar energy in heating water, .cooking foods, concentrating sunlight, and producing electricity.
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Materials

• Paint brush
• Thermometer (outdoor type)
• Newspaper
• Aluminum foil
• Water
• Large, plastic glass
• Empty aluminum 12-ounce (355 milliliter) soft drink can
• Black paint or spray paint (flat, not shiny)

Download Student Worksheet & Exercises

Procedure
Go outside and spread a sheet of newspaper on the ground. Place an empty aluminum soft drink can on the newspaper. Have an adult help you paint the outside of the aluminum can. You can use a brush and can of paint or spray paint. Be sure to use paint that is suitable for a metal surface.  The paint should give you a flat (not shiny) surface. Be sure not to get the paint on anything but the can and newspaper. After painting, set the can where the paint can dry overnight.

You will need to do the rest of this experiment on a warm, sunny day. Partially fill a large, plastic glass with cool tap water. Check the temperature of the water with a thermometer. Pour the water from the plastic glass into the painted black can, completely filling the can. Pour out any extra water remaining in the plastic glass. Cover the can’s opening with a small piece of aluminum foil about the size of a quarter.

Set the black can outside in a sunny spot. Pick a place where the sun will shine on the can all day. (You do not want the can to be in the shade.)

After the can of water has been in the sunshine for about four hours, pour the water into the large, plastic glass. Check the temperature of the water with the thermometer. Feel the outside of the can.

Observations

What was the temperature of the cool tap water when it was first placed into the black can? What is the temperature of the water after it was heated in the can for four hours? Does the outside of the can feel hot?

Discussion

You should find a significant increase in the temperature of the water that was left in the black can during the day. The tap water initially may be about 21°C (70°F), but after the water has been heated inside the can, the temperature should rise to more than 38°C (100°F). The exact temperature you achieve in your miniature, solar water heater (black can) will depend on your location and the time of year. However, you should find that the water temperature will go much higher than the temperature of the outside air.

The electromagnetic radiation from the sun includes ultraviolet, visible, and infrared radiation. Ultraviolet radiation is the type of sunlight that causes tanning of skin. Visible radiation is the type of sunlight we see with our eyes. Infrared radiation is the type of sunlight that we feel as heat when the sun is shining on our skin. All these forms of solar radiation have energy associated with them.

When solar energy from the sun’s electromagnetic radiation strikes a black surface, solar energy is converted to heat energy and the surface is warmed. Other colors will absorb solar energy, but lightly colored surfaces tend to reflect the light, while darker colors absorb the solar energy. You may have noticed this difference if you ever walked barefoot on a dark road on a hot summer day.

Direct solar energy is not hot enough for cooking. The higher temperatures required for cooking or for changing water to steam require concentrating the energy of sunlight with mirrors or lenses. However, directly absorbed solar energy is hot enough for heating homes and producing hot water with little or no energy costs.

When we turn on a hot water faucet at a sink, water is taken from a hot water tank. In industrialized countries, we usually heat water using electricity or natural gas and store the hot water in this insulated tank. However, around the world, there are millions of solar heaters used for heating water.

Solar water heaters use a black metal plate covered with insulated glass. These solar heaters are usually placed on rooftops to receive the maximum amount of sunlight. Water flows through tubes beneath the black metal plates. Solar energy heats the black metal plates and the water passing in tubes underneath the plates. The heated water is piped to a storage tank, where it is kept until needed. If the location of the solar heater is not consistently sunny, then an auxiliary heater-using electricity or natural gas-is sometimes used to heat the water.

Other Things to Try

Repeat this experiment covering the black can with a large glass jar. This glass should help trap the heat and make the water get even hotter. What is the maximum temperature you can get with this type of solar heater?

Repeat this experiment and check the temperature of the water each half hour for three hours during the middle of the day. Quickly check the temperature of the water, then return the water to the black metal can. Write down the time that you checked the water, and next to the time, write down the temperature. How long does it take for the water to reach the maximum water temperature?

Repeat this experiment with an unpainted can and a painted can. After one hour, how do the temperatures of the water in each can compare?

Repeat this experiment on a cloudy day. Does the water in the can get as hot without sunshine?

Exercises

1. The solar energy that hits the earth is responsible for what proportion of the energy on our planet?
   1. Nearly all of it
   2. About 50%
   3. 25%
   4. None of these
2. Name one way that the physical earth uses the earth’s energy:
3. True or false: Solar power is generally less expensive than other forms of power.
   1. True
   2. False

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The United States has large reserves of coal, natural gas, and crude oil which is used to make gasoline. However, the United States uses the energy of millions of barrels of crude oil every day, and it must import about half its crude oil from other countries.

Burning fossil fuels (oil, coal, gasoline, and natural gas) produces carbon dioxide gas. Carbon dioxide is one of the main greenhouse gases that may contribute to global warming. In addition, burning coal and gasoline can produce pollution molecules that contribute to smog and acid rain.

Using renewable energy-such as solar, wind, water, biomass, and geothermal-could help reduce pollution, prevent global warming, and decrease acid rain. Nuclear energy also has these advantages, but it requires storing radioactive wastes generated by nuclear power plants. Currently, renewable energy produces only a small part of the energy needs of the

United States. However, as technology improves, renewable energy should become less expensive and more common.

Hydropower (water power) is the least expensive way to produce I electricity. The sun causes water to evaporate. The evaporated water falls to the earth as rain or snow and fills lakes. Hydropower uses water stored in lakes behind dams. As water flows through a dam, the falling water turns turbines that run generators to produce electricity.

Currently, geothermal energy (heat inside the earth), biomass (energy from plants), solar energy (light from concentrated sunlight), and wind are being used to generate electricity. For example, in California there are more than sixteen thousand (16,000) wind turbines that generate enough power to supply a city the size of San Francisco with electricity.

In addition to producing more energy, we can also help meet our energy needs through conservation. Conservation means using less energy and using it more efficiently.

In the following experiments, you will use wind to do work, examine how batteries can store energy, and see how insulation can save energy.
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Materials

• Pinwheel (can be purchased or madefrom construction paper)
• Paper clips
• Tape
• Small shoe box  (children’s size)
• Electric fan
• Lightweight string  (about 4 feet long)
• Plastic straw (longer than the width of the shoe box)
• Hole punch

Download Student Worksheet & Exercises

Procedure

In this activity, you will try to use the energy in the wind to lift a set of six paper clips. You will first need to construct your windmill.

Use a hole punch to punch holes in the opposite sides across the width of a small, cardboard shoe box. Use the narrow sides of the box so the two holes are less than six inches (15 centimeters) apart. Make sure the holes are directly opposite each other. Place a plastic straw through the two holes. You may need to use the hole punch to enlarge the holes so the straw can rotate within the holes. The ends of the straw should extend out either side of the box.

Use the blades from a purchased pinwheel, or cut and fold a square piece of construction paper into the shape of a pinwheel. Next you will need to attach the pinwheel blades to one end of the straw. Partially unfold a small paper clip and insert the larger end into the straw. Push the straightened end of the paper clip through the center of the pinwheel. Bend this end of the paper clip and tape it to the outside of the pinwheel.

Set the electric fan on a table or countertop. Hold the shoe box so that the pinwheel is free to turn. HAVE AN ADULT PLUG IN AND TURN ON THE FAN. Move the windmill box to direct the breeze from the fan toward the blades of the pinwheel. Move the box until you find the best angle of the fan to the pinwheel so that the pinwheel turns freely and rapidly.

Turn off the fan. Now tape one end of the string to the side of the straw with no pinwheel just outside the box, and wrap the string around the straw a few times. Tie the other end of the string to a paper clip. Attach five other paper clips to the paper clip tied to the string. Allow the string to hang down so that the paper clips on the end of the string rest on the floor.

Now, you will test to see if your windmill can convert wind power to do work and lift the paper clips off the ground. Turn on the fan and hold the box where you did before to make the pinwheel turn.

Observations

Does the windmill turn the straw? Does the string wrap around the straw as the straw turns? What happens to the paper clips?

Discussion

You should observe the straw shaft turning as the wind from the fan is directed toward the blades of the pinwheel. As the pinwheel turns, it should wrap the string around the straw and lift the paper clips into the air. Your windmill converts the energy of the wind to work and lifts the weight of the paper clips. If your windmill is not working, then examine all the parts.

Compare your setup to the drawing, and see if any changes need to be made in your construction.

One way to store the energy produced by a windmill is to lift a weight. When the weight is allowed to fall, work can be produced. Weights in a grandfather clock are used to store energy and can run a clock for a week or longer. A windmill’s energy can be used to pump water to a storage area at a higher elevation. Later, this water can be allowed to fall through a turbine which turns a generator and produces electricity.

Electricity can also be produced directly from wind power. The shaft, or rod to which the windmill blades are attached, can be used to turn a generator. A generator or dynamo is used to convert mechanical energy into electrical energy. Power conversion units can change the direct current that wind generates to an alternating current. The alternating current can be fed directly into utility lines and used in our homes.

The sun is the original source of wind power. Without the sun to heat the earth, there would be no wind. The energy of the sun heats the earth, but all parts of the earth are not at the same temperature. These differences in temperature are responsible for global and local patterns of wind. For example, during the day a constant wind blows from the sea toward the land along coastal regions. Air above the hotter land rises and cooler, heavier air above the ocean moves in to take its place.

The power of the wind can be harnessed to do work. For at least 4,000 years, the wind has been used to move sailing ships. The wind has enough power to move ships across oceans and around the world.

For at least 1,000 years, windmills have been used for pumping water and turning

stones to grind grain. Millions of windmills have been used on the plains of America, Africa, and Australia to pump water from deep wells for livestock and humans.

In this century, windmills or wind engines have been used to generate electricity. Over 15,000 wind engines were installed in California in the 1980s. These wind engines have the capability to produce up to 1.5 billion watts of electricity. In California in 1987, wind was used to produce as much electricity as the city of San Francisco uses in an entire year.

Other Things to Try

Repeat this experiment and find the maximum weight you can lift with your windmill. Try more paper clips or try a heavier weight such as a pen.

List some of the problems associated with using windmills. What happens when the wind is blowing too gently? What happens if the wind blows strongly, such as in a storm? Do you think the area where you live is windy enough for wind engines to produce electricity?

Exercises

1. Name three sources of renewable energy:
2. What does the sun have to do with wind?
3. Name three examples of wind power in historical or current usage:

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Temperature is a measure of the average hotness of an object. The hotter an object, the higher its temperature. As the temperature is raised, the atoms and molecules in an object move faster. The molecules in hot water move faster than the molecules in cold water. Remember that the heat energy stored in an object depends on both the temperature and the amount of the substance. A smaller amount of water will have less heat energy than a larger amount of water at the same temperature.

Increasing the temperature of a large body of water is one way to store heat energy for later use. A large container filled with salt water, called brine, may be used to absorb heat energy during the day when it is warm. This energy will be held in the salt water until the night when it is cooler. This stored heat energy can be released at night to warm a house or building. This is one way to store the sun’s heat energy until it is needed.

Solar ponds are used to store energy from the sun. Temperatures close to 100°C (212°F) have been achieved in solar ponds. Solar ponds contain a layer of fresh water above a layer of salt water. Because the salt water is heavier, it remains at the bottom of the pond-even as it gets quite hot. A black plastic bottom helps absorb solar energy from sunlight. The water on top serves to insulate and trap the heat in the pond.

In a fresh water pond, as the water on the bottom is heated from sunlight, the hot water becomes lighter and rises to the top of the pond. This convection or movement of hot water to the top tends to carry away excess heat. However, in a salt water pond, there is no convection so heat is trapped. In Israel a series of salt water, solar ponds were developed around the Dead Sea. The heat stored in these solar ponds has been used to run turbines and generate electricity.
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Materials

• Two paper cups
• Measuring cups
• Hot water
• Watch or clock
• Sink
• Refrigerator (with freezer compartment)

Download Student Worksheet & Exercises

Procedure

Turn on the hot water faucet of a sink and wait several minutes until the water is hot. Be careful not to burn yourself with this hot water. Add one-fourth cup of this hot water to the first paper cup. Add one cup of hot water to the second paper cup. Place both of these cups in the freezer compartment of a refrigerator.

After thirty minutes check the water in each cup.  Return the cups to the freezer compartment and check them again after fifteen minutes. Keep checking the cups each fifteen minutes until the water in one of the cups is frozen.

Observations

Does the water in the cups freeze at the same time? Does the water in one of the cups freeze first? How long does it take for the water to freeze?

Discussion

You will probably observe that the smaller amount of water in the first cup freezes prior to the larger amount of water in the second cup. Both cups were filled with the same hot water. However, even though the water in both cups was at the same temperature, they did not freeze at the same time. The amount of heat energy stored by the water depends on both the temperature and the amount of water.

We expect that the more heat energy stored in the cup, the longer it takes the water in the cup to freeze. Since one cup of water has more heat energy than one-fourth cup of water, it takes the larger amount of water longer to freeze.

Other Things to Try

Place one-half cup of hot tap water in one cup.  Place one-half cup of cool tap water in a second cup. Put both cups in the freezer compartment of a refrigerator and check them every fifteen minutes until the water freezes solid. Which cup of water do you think has more heat energy? Which cup of water do you think will freeze first?

Place one cup of water in one paper cup and one-fourth cup of water in a second paper cup. Put both cups in the freezer of a refrigerator and leave overnight. The next day remove both cups of frozen water. Set the two cups out in the room. Observe the time it takes each piece of ice to melt. Which piece of ice do you think will melt first? Which piece will require more heat energy to cause it to melt?

Exercises

1. What type of heat transfer is at work in a solar pond?
   1. Kinetic
   2. Conduction
   3. Potential
   4. Convection
   5. Radiation
2. What units do we use to measure energy?
   1. Kilowatts
   2. Joules
   3. Newtons
   4. Kilowatt-hours
3. Draw a diagram of a solar pond in the space below:

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Without the sun, there would be no life on Earth. The sun warms the earth, generates wind, and carries water into the air to produce rain and snow. The energy of the sun provides sunlight for all the plant life on our planet, and through plants provides energy for all animals.

The sun is like a giant furnace in which hydrogen nuclei (atoms without electrons) are constantly smashed together to form helium nuclei. This process is called nuclear fusion. In this process, 3.6 billion kilograms (8 billion pounds) of matter are converted to pure energy every second. The temperature in the sun exceeds 15 million degrees.

Nuclear fusion is one kind of energy. Other forms of energy include: mechanical energy, heat, electrical energy, chemical energy, and light. Mechanical energy is the energy of organized motion, such as a turning wheel. Heat is the energy of random motion, such as a cup of hot water. Electrical energy is the energy of moving charged particles or electrons, such as a current in a wire. Chemical energy is the energy stored in bonds that hold atoms together. Light is any form of electromagnetic waves, such as X rays, microwaves, radio waves, ultraviolet light, or visible light.

Energy can be converted from one from to another. For example, the nuclear energy of the sun is converted to light, which goes through space to the earth. Solar collectors of mirrors can be used to focus some of that light to heat water to steam. This steam can be used to turn a turbine, which can power a generator to produce electricity.

Most of our energy needs are met by burning fossil fuels such as coal, oil, gasoline, and natural gas. The chemical energy stored in these substances is released by burning these fuels. When fossil fuels burn, they combine with oxygen in the air and produce heat and light.

Fossil fuels are not renewable. When they are used up, they are gone forever. However, renewable energy sources such as wind, sun, geothermal, biomass and water power are renewable. They can be used over and over to generate the energy to run our society.

Tremendous amounts of renewable energy are available. For example, the solar energy that falls on just the road surfaces in the United States is equal to the entire energy needs of the country. Although there are sufficient amounts of renewable energy, we must improve our methods of collecting, concentrating, and converting renewable energy into useful forms.

In the following experiments, you will learn something about the amount of energy the sun produces at the earth’s surface and how heat energy can be stored.
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Materials

• Water
• Disposable, aluminum pie pan
• Paint brush
• Measuring cups
• Watch or clock
• Newspaper
• Black paint or spray paint (flat, not shiny)

Procedure

Go outside and spread out a sheet of newspaper. Place an aluminum pie pan on the newspaper. Carefully bend one spot on the edge of the pie pan to make a spout shape. This will allow you to more easily pour water out of the pan. Have an adult help you paint the inside of the aluminum pie pan. You can use a brush and a can of paint or spray paint. Be sure not to get the paint on anything except the disposable pie pan and the newspaper. After painting, set the pie pan where the paint can dry overnight.

You will need to do the rest of this experiment on a warm, sunny day. You do not want the pie pan to be in the shade. Set the aluminum pie pan in a warm, sunny spot. The sun will need to constantly shine on the pie pan. The black color of the pie pan allows it to absorb, rather than reflect, solar energy. You will need to begin the experiment about

11:00 A.M., so the solar heating will be done when the sun is high in the sky.

Add exactly one cup of water to the pie pan. Wait four hours while the sun is shining on the pan of water. After exactly four hours of sunshine, carefully pour the remaining water from the pie pan into a one-half or one-fourth measuring cup. Use these measuring cups to estimate the amount of remaining water to the nearest one-eighth of a cup.

Observations

Is the amount of water in the pie pan less than when you began the experiment? How much water is left in the pie pan after four hours of sunlight?

Discussion

You will probably observe that the amount of water in the pie pan is less after four hours of sunlight exposure. Where did the water go? As the sunlight shines on the dark surface of the painted pie pan, solar energy is absorbed and heats the pan and the water. This energy causes a portion of the water to evaporate. As water evaporates, it leaves the liquid form and goes into the air as a gas (water vapor). You will probably find that some, but not all, of the water evaporated.

Scientists use the unit of joule as a measure of energy. However, you may find it helpful to think in units of dietary calories instead of joules. One dietary calorie is equal to 4,184 joules of energy. One cup of breakfast cereal with one-half cup of milk would have about 240 dietary calories, or approximately 1,000,000 joules of energy. Although the earth receives only a tiny portion of the total energy output of the sun, the earth has a constant supply of 173 million billion (173,000,000,000,000,000) watts of solar power. A watt is a unit of power equal to a joule of energy used per second. For comparison, a typical light bulb to run a lamp in your home might require 100 watts of power. A million watts could supply the energy needs of about 500 average American homes.

Use the table below to determine the solar energy required to evaporate a certain amount of water. The amount of water remaining in the pan will allow you to determine how much energy was used, how much power was used, and the amount of power per area.

Your results will probably be in the middle range of this table. For example, if one-half of your water evaporated, then the water remaining would be one-half cup. Thus, the energy used to evaporate this water would be 289,000 joules of energy. This energy would give a power of 20 watts, and a power per area of 800 watts per square meter (watts / meter²).

The following procedure was used to generate the numbers in the Table. It is known that it takes 578,000 joules of energy to evaporate one cup of water. This known energy per cup is multiplied by the fraction of a cup that was evaporated. This gives the solar energy used to evaporate the water in the pie pan. The energy is divided by the number of seconds in four hours (14,400 seconds). This gives the power of the solar energy striking the pie pan, since a watt is equal to a joule per second. Finally, the power (in watts) is divided by the surface area of the pie pan (0.025 square meters) to give the power per area.

When the sun is overhead, the intensity of solar energy can be as much as 1,000 watts per square meter. If all of this energy could be converted to electricity, one square meter of sunshine would be enough to run ten 100-watt light bulbs. However, our current solar cells that convert sunlight to electricity are able to change only about 15 percent of the light to electricity.

You can see from this experiment that there is tremendous energy available from our sun. Most of this energy warms our planet or is reflected back into space. Among other things, the remaining portion of energy powers our water cycle, producing rain and snow, or provides plants with the energy they need to live.

Scientists and engineers are learning more about trapping solar energy and converting it to useful power. It has been estimated that all forms of potentially available renewable energy (wind, water, biomass, and direct solar) have an energy equivalent to 80 trillion barrels of oil. In other words, one year of renewable solar energy is 5,000 times greater than the current yearly energy needs of the United States. In comparison, it has been estimated that all the remaining coal, oil, natural gas, and other potential nonrenewable energy reserves of the United States are equal to about 8 trillion barrels of oil.

Since we do not yet know how to use a significant portion of this renewable energy, much work remains to be done. In the remainder of this book you will learn more about our current ability to use renewable energy and the promise it may hold for the future.

Other Things to Try

Repeat this experiment using different amounts of water on different days and compare the solar power you find.

Repeat this experiment in the late afternoon, when the sun is lower in the sky. How do your result compare to this experiment?
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Fossil fuels, which include petroleum, natural gas, and coal, supply nearly 90 percent of the energy needs of the United States and other industrialized nations. Because of their high demand, these nonrenewable energy resources are rapidly being consumed. Coal supplies are expected to last about a thousand years.

We must find other sources of energy to meet the increasing fuel demands of modern society. Important alternate sources of energy include: solar, wind, biomass, hydroelectric, geothermal, nuclear, and tidal energy.

One of the benefits of using alternate sources of energy is that many of them are “clean.” This means that they do not cause pollution. Also, many alternative energy sources are renewable energy sources. They are replaced naturally-such as plant life-or are readily available – such as the sun and wind. In addition, the use of renewable forms of energy will allow us to stretch out our current supply of fossil fuels so they will last longer.

In this chapter you will learn how biomass, or organic matter, can be an important energy source. Plants are the most important biomass energy source. Plant material can be burned directly-as with wood-or it can be converted into a fuel by other means. In the experiments that follow you will explore: how water can be heated by composting grass, how a peanut burns, and how corn syrup can be made into ethyl alcohol.
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Materials

• Freshly cut grass clippings
• Cooking thermometer (optional)
• Empty two-liter plastic drink bottle
• Rake
• Water
• Styrofoam cup

Procedure

Ask an adult to help you collect freshly cut grass clippings. You will need enough grass clippings to fill about two large grocery bags. Rake the grass clippings into a pile on a shady spot in the yard. In some parts of the country you will only be able to do this in the spring and summer months when grass grows.

Fill a two-liter plastic bottle with cold water. Starting at the top of the pile dig a hole down into the grass clippings just large enough for the plastic bottle. Place the plastic bottle in the hole, and then fill around it with grass clippings. The top of the plastic bottle should stick out of the pile of grass clippings slightly.

Check the water in the bottle after it has been in the pile of grass clipping for at least twenty-four hours. If you have a cooking thermometer, place it in the bottle for thirty seconds and then read the temperature on the thermometer. If you do not have a cooking thermometer, carefully remove the bottle of water from the pile of grass clippings. Feel the sides of the plastic bottle. CAUTION-THE BOTTLE MAY BE VERY WARM, SO AVOID BURNING YOURSELF. Pour some of the water into a Styrofoam cup and look for water vapor rising from the cup. Place the bottle back into the pile of grass clippings and check it again each day for several days.

Observations

After twenty-four hours in the grass clippings, is the water in the plastic bottle warm when you check it? If you check the water with a thermometer, what is the temperature of the water?

When you pour some of the water into a Styrofoam cup, do you see water vapor rising from the cup?

How many days does the water remain warm?

Does the pile of grass clippings become smaller after a few days? What does the pile of grass clippings look like when the water is no longer warm?

Discussion

The water in the plastic bottle should be warm after the bottle has been in the pile of grass clippings for twenty-four hours. The heat that warms the water comes from the pile of grass clippings, which is decomposing or composting.

The decomposition of dead plant and animal material is nature’s way of recycling important chemical substances. Complex chemical substances in dead plant and animal material are broken down into simple chemical substances during the process. These simpler chemical substances then become nutrients for living plants and soil animals.

Heat is given off during the decomposition process. The more material that is decomposing, the more heat is produced. In this experiment, a large amount of heat is given off by the decomposing grass clippings. This is because you started with a large pile of grass clippings, and grass clippings decompose quickly.

A pile of decomposing grass clippings can reach a temperature of over 71°C (160°F). The water in the bottle may absorb enough heat from the decomposing grass to reach a temperature as high as 60°C (140°F) after a day or two. For comparison, most household hot water heaters are set to deliver hot water with a temperature between 54°C (130°F) and 71°C (160°F).

Other Things to Try

How much water can you heat with composting grass clippings? To find out, repeat this experiment with a one-gallon plastic milk jug filled with water. Does the water in the jug become warm?

Repeat this experiment, but remove the bottle of water from the pile of grass clippings after twenty-four hours. Fill a second two-liter plastic bottle with cold water from a sink faucet and place it into the pile of grass clippings. Does the water in this bottle become warm after a couple of hours?

Is there a minimum amount of grass clippings that are needed to make enough heat to heat the water in a two-liter plastic bottle? To find out, surround a two-liter plastic bottle filled with water with just enough grass clippings to cover it. Does the water become warm after twenty-four hours?
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A peanut is not a nut, but actually a seed. In addition to containing protein, a peanut is rich in fats and carbohydrates. Fats and carbohydrates are the major sources of energy for plants and animals.

The energy contained in the peanut actually came from the sun. Green plants absorb solar energy and use it in photosynthesis. During photosynthesis, carbon dioxide and water are combined to make glucose. Glucose is a simple sugar that is a type of carbohydrate. Oxygen gas is also made during photosynthesis.

The glucose made during photosynthesis is used by plants to make other important chemical substances needed for living and growing. Some of the chemical substances made from glucose include fats, carbohydrates (such as various sugars, starch, and cellulose), and proteins.

Photosynthesis is the way in which green plants make their food, and ultimately, all the food available on earth. All animals and nongreen plants (such as fungi and bacteria) depend on the stored energy of green plants to live. Photosynthesis is the most important way animals obtain energy from the sun.

Oil squeezed from nuts and seeds is a potential source of fuel. In some parts of the world, oil squeezed from seeds-particularly sunflower seeds-is burned as a motor fuel in some farm equipment. In the United States, some people have modified diesel cars and trucks to run on vegetable oils.

Fuels from vegetable oils are particularly attractive because, unlike fossil fuels, these fuels are renewable. They come from plants that can be grown in a reasonable amount of time.
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Materials

• Shelled peanut
• Small pair of pliers
• Match or lighter
• Sink

Download Student Worksheet & Exercises

Procedure

ASK AN ADULT TO HELP YOU WITH THIS EXPERIMENT. DO NOT DO THIS EXPERIMENT BY YOURSELF. The fuel from the peanut can flare up and burn for a longer time than expected.

Close the drain in the kitchen sink. Fill the sink with water until the bottom of the sink is just covered.

Using a small pair of pliers, hold the peanut over the sink containing water. Ask an adult to hold the flame of a lit match or lighter directly under the peanut. When the peanut starts to burn, the lit match or lighter can be removed.

Allow the peanut to burn for one minute. MAKE SURE AN ADULT REMAINS PRESENT AND MAKE SURE TO HOLD THE PEANUT OVER THE SINK. To extinguish the burning peanut, drop it into the water. After you have extinguished the peanut, allow it to cool and then examine it carefully.

Observations

How long does it take for the peanut to start to burn? Does the peanut burn with a clean flame or a sooty flame? What color is the flame? What color does the peanut turn when it burns? Did the size of the peanut change after it has burned for several minutes?

Discussion

You should find that the peanut ignites and burns after a lit match or lighter is held under it for a few seconds. Although you only let the peanut burn for one minute as a safety measure, the peanut would burn for many minutes.

In this experiment, when the peanut burns, the stored energy in the fats and carbohydrates of the peanut is released as heat and light. When you eat peanuts, the stored energy in the fats and carbohydrates of the peanut is used to fuel your body.

Other Things to Try

Hold one end of a piece of uncooked spaghetti in a pair of pliers. Ask an adult to hold the flame of a lit match or lighter under the other end of the spaghetti. When the spaghetti starts to burn, place it in an aluminum pie pan that is in the sink. Make sure to extinguish the burning spaghetti with water when you are finished with the experiment. How does the burning of the spaghetti compare with the burning of the peanut?

Exercises 

1. What is the process called where plants get food from the sun?
   1. Osteoporosis
   2. Photosynthesis
   3. Chlorophyll
   4. Metamorphosis
2. Where does all life on the planet get its food?
3. List two ways that we could use the energy in a peanut:

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Yeast is a simple living organism that can break down sugars into ethyl alcohol (ethanol) and carbon dioxide. The process by which yeast breaks down sugars into ethyl alcohol and carbon dioxide is called fermentation.

The tiny gas bubbles rising in the liquid mixture in the bottle are carbon dioxide gas bubbles that are made during the fermentation. The balloon on the bottle expands and becomes inflated because it traps the carbon dioxide gas being produced.

The ethyl alcohol that is made during fermentation stays in the liquid mixture. When fermentation is finished, the liquid mixture usually contains about 13 percent ethyl alcohol. The rest of the liquid is mostly water.

The ethyl alcohol can be concentrated by a process called distillation. During distillation, the liquid fermentation mixture is heated to change the ethyl alcohol and some of the water into a vapor. The vapor is then cooled to change it back into a liquid. This distilled liquid contains 95 percent ethyl alcohol and 5 percent water. The remaining water can be removed by special distillation methods to give pure ethyl alcohol.

In some areas of the United States, ethyl alcohol is blended with gasoline to make a motor fuel known as gasohol. About 8 percent of the gasoline sold in the United States is gasohol.

Gasohol burns more cleanly than pure gasoline. This results in fewer pollutants being released into the air. The use of gasohol as a motor fuel is particularly important in cities that have a lot of smog.

Corn syrup is a mixture of simple and complex sugars and water. It is made by breaking down the starch in corn into sugars. The process is called digestion. In this experiment you changed the sugars in corn syrup using yeast. Much of the ethyl alcohol used to prepare gasohol is made by fermenting corn and corn sugar.

Over one billion gallons of ethyl alcohol are made each year by fermentation of sugars from grains such as corn. Ethyl alcohol is a renewable energy source when it is made by fermenting grains such as corn. This is because the grains, such as corn, are easily grown.

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Materials

• One package of yeast
• Balloon
• Water
• Measuring spoons
• Corn syrup
• Measuring cup
• Empty, two-liter plastic drink bottle
•  Funnel (optional)
• Sink or bucket

 Procedure

Remove the paper label from around an empty, two-liter, plastic drink bottle. Add two cups of water and one package of yeast to the bottle. Swirl the bottle to mix the water and yeast.

Next, add one-quarter cup of corn syrup to the bottle. You may want to use a small funnel to help you add the corn syrup to the bottle. Swirl the bottle to mix the contents.

Place a deflated balloon over the neck of the bottle. Make sure the balloon fits securely over the neck. Place the bottle in a sink or bucket. Check the bottle and balloon after two hours, and then again after four hours. Finally, check the bottle and balloon after twenty-four hours.

When you have finished with the experiment, pour the contents of the bottle down the sink. Then rinse the bottle and sink with water.

Observations

What color is the yeast mixture? Does the balloon start to inflate after an hour or two? Can you see gas bubbles rising to the surface of the yeast mixture? Does the balloon grow larger with time?

Discussion

You should find that soon after you mix together the yeast, water, and corn syrup, changes start to take place in the bottle. You should notice that a foam forms on top of the liquid mixture. You should also see tiny gas bubbles rising to the surface of the liquid. Also, you should notice that the balloon begins to inflate and become large.

Other Things to Try

Repeat this experiment using one tablespoon of table sugar instead of corn syrup. You should find that yeast can also ferment table sugar into ethyl alcohol and carbon dioxide. Table sugar is made from sugar cane and sugar beets. Since sugar cane and sugar beets are renewable plants, ethyl alcohol made from fermenting sugar from these plant products is another renewable energy source.

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The atoms in a solid, as we mentioned before, are usually held close to one another and tightly together. Imagine a bunch of folks all stuck to one another with glue. Each person can wiggle and jiggle but they can’t really move anywhere.

Atoms in a solid are the same way. Each atom can wiggle and jiggle but they are stuck together. In science, we say that the molecules have strong bonds between them. Bonds are a way of describing how atoms and molecules are stuck together.

There’s nothing physical that actually holds them together (like a tiny rope or something). Like the Earth and Moon are stuck together by gravity forces, atoms and molecules are held together by nuclear and electromagnetic forces. Since the atoms and molecules come so close together they will often form crystals.

Try this experiment and then we will talk more about this:
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Here’s what you need:

• 50 pennies
• ruler

 
Download worksheet and exercises

Lay about 20-50 pennies on the table so that they are all sitting flat on the table. Now, use the ruler (or your hand) to push the pennies toward one another so that you have one big glob of pennies on the table all touching one another. Don’t push so hard that they pile on top of one another. Just get one nice big flat blob of pennies.

Pretty simple huh? However, take a look at the pennies, do you notice anything? You may notice that the pennies form patterns. How could that happen? You just shoved them together you didn’t lay them out in any order. Taa daa! That’s what often happens when solids form.

The molecules are pulled so close to one another that they will form patterns, also known as matrices. These patterns are very dependent on the shape of the molecule so different molecules have a tendency to form different shaped crystals. Salt has a tendency to be “cubey”. Go take a look… and you’ll find that they are like little blocks!

Water has a tendency to from triangle or hexagon shapes which is why snowflakes have six sides. Your pennies also form a hexagon shape. Solids don’t always form crystals but they are more common than you might think. A solid that’s not in a crystalline form is called amorphous. Before you put your pennies away I want you to notice one more thing.

Here’s what you do:

1. Take your pennies and lay them flat on the table.

2. Push them together so they all touch without overlapping.

3. Place your ruler on the right hand side of your penny blob so that it’s touching the bottom half of your pennies.

4. Slowly push the ruler to the left and watch the pennies.

You may have noticed that the penny “crystal” split in quite a straight line. This is called cleavage. Since crystals form patterns the way they do they will tend to break in pretty much the same way you saw your pennies break.

Break an ice cube and take a look. You may see many straight sections. This is because the ice molecules “cleave” according to how they formed. The reason you can write with a pencil is due to this concept. The pencil is formed of graphite crystal. The graphite crystal cleaves fairly easily and allows you to write down your amazing physics discoveries!

(The image here is a graphite crystal.) [/am4show]

Crystals are formed when atoms line up in patterns and solidify.  There are crystals everywhere — in the form of salt, sugar, sand, diamonds, quartz, and many more!

To make crystals, you need to make a very special kind of solution called a supersaturated solid solution.  Here’s what that means: if you add salt by the spoonful to a cup of water, you’ll reach a point where the salt doesn’t disappear (dissolve) anymore and forms a lump at the bottom of the glass.

The point at which it begins to form a lump is just past the point of saturation. If you heat up the saltwater, the lump disappears.  You can now add more and more salt, until it can’t take any more (you’ll see another lump starting to form at the bottom).  This is now a supersaturated solid solution.  Mix in a bit of water to make the lump disappear.  Your solution is ready for making crystals.  But how?

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Here’s what you need:

• pencil or wooden skewer
• string
• glass jar (cleaned out pickle, jam or may jars work great)
• 8 cups of sugar
• 3 cups water
• paper clip
• adult help and a stove
• food coloring  is optional but fun!

If you add something for the crystals to cling to, like a rock or a stick, crystals can grow.  If you “seed” the object (coat it with the stuff you formed the solution with, such as salt or sugar), they will start forming faster. If you have too much salt (or other solid) mixed in, your solution will crystallize all at the same time and you’ll get a huge rock that you can’t pull out of the jar.  If you have too little salt, then you’ll wait forever for crystals to grow. Finding the right amount takes time and patience.

 
Download Student Worksheet & Exercises

1. If you plan on eating the sugar crystal when you’re done you probably want to boil water with the jar and the paper clip in it to get rid of any nasties. Be careful, and don’t touch them while they are hot.

2. Tie one end of the string to the pencil and the opposite end to the paper clip.  (You can alternatively use a skewer instead of a piece of string to make it look more like the picture above, but you’ll need to figure out a way to suspend the skewer in the jar without touching the sides or bottom of the jar.)

3. Wet the string a bit and roll it in some sugar. This will help give the sugar crystals a place to start.

4. Place the pencil across the top of the jar. Make sure the clip is at the bottom of the jar and that the string hangs straight down into the jar. Try not to let the sting touch the side of the jar.

5. Heat 3 cups of water to a boil

6. Dissolve 8 cups of sugar in the boiling water (again be careful!). Stir as you add. You should be able to get all the sugar to dissolve. You can add more sugar until you start to see undissolved bits at the bottom of the pan.  If this happens, just add a bit of water until they disappear.

7. Feel free to add some food coloring to the water.

8. Pour the sugar water into the jar. Put the whole thing aside in a quiet place for 2 days to a week. You may want to cover the jar with a paper towel to keep dust from getting in.

You should see crystals start to grow in about 2 days. They should get bigger and bigger over the few days. Once you’re happy with how big your crystals get, you can eat them! It’s nothing but sugar! (Be sure to brush your teeth!)  This one (left) us about 6 months old.

There you go! Next time you hold a pencil, throw a ball, or put on a shoe try to keep in mind that what you’re doing is using an object that is made of tiny strange atoms all held tightly together by their bonds.

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Popcorn rocks are different than regular dolomite samples because they have a lot more magnesium inside. This was first discovered by a geology professor in the 1980s who was dissolving the limestone around fossils he was studying in his rock samples. When he placed samples of this type in the acid to dissolve, it didn’t dissolve but instead grew new crystals!

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Materials:

• “Flowering Rock” dolomite samples
• Distilled white vinegar (acetic acid)
• Disposable cup or glass jar
• Penny
• Nail
• Streak plate
• Water in a graduated container
• Scale that measures in grams
• Longwave UV light source
• Sunlight

Download worksheet and exercises

Dolomite is made of calcium magnesium carbonate (CaMg(CO3)2 and is both a mineral and a rock. Dolomite comes in all kinds of colors, including white, gray, pink, peach, yellow and orange … even colorless. Dolomite gives a white streak, which is hard to see on a white streak plate, and the hardness ranges from 3.4 to 4 on the Moh’s hardness scale. Specific gravity for dolomite is 2.8 to 3, with a vitreous (glassy), pearly luster and rhombohedra cleavage on two planes and conchoidal fracture on the third. It’s brittle (think tenacity), and is usually found around limestone. Dolomite is a chemical rock, since it reacts to acid. Dolomite fluoresces bluish-white when placed under a longwave UV light, and pink when exposed to a shortwave UV light.

1. You’re first going to classify dolomite and test it for certain properties, and then you’ll grow crystals all over it. If you don’t have a UV light, skip it and perform the rest of the tests.
2. Complete the first data table for the sample before following the instructions on the video. You are looking for the color, streak, hardness, density, luster, cleavage, fracture, tenacity, acid reaction, and fluorescence.
3. Don’t wash your dolomite sample. You want the dust layer on top so the crystals start growing more quickly.
4. Place the sample in your glass jar.
5. Pour the vinegar into the cup (not directly on your sample) until it’s nearly submerged.
6. Move your experiment to a warm location.
7. Observe your rock formation over the next week and record your observations in the second data table. You can opt to take pictures and paste them into the data table.
8. When all the vinegar has evaporated, remove the sample and put on display (after recording your last observation).

Exercises

1. What would happen if you warmed the vinegar first, and placed it on a heating pad during your experiment?
2. What is it in the dolomite samples that make the aragonite crystals grow?
3. What else can you try instead of vinegar?

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Luster is the way a mineral reflects light, and it depends on the surface reflectivity.

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Materials

• Sunlight
• Rock samples (in the video: pyrite, fluorite, and serpentine)

Download worksheet and exercises

Every mineral has a particular luster, but some have different luster on different samples. Since it’s gauged by eye and not a scientific instrument, there’s quite a lot to be left to the observer when describing it. Luster is not usually used to identify minerals, since it’s so subjective.

That said, it is useful when describing a sample’s surface, so hold up yours to the light and use the descriptions below to find the one that best describes what you see.

• Metallic or splendent luster are found in highly reflective minerals, like gold.
• Submetallic luster is found in minerals that have a similar luster to metal, but it’s a bit duller and less reflective. These minerals are opaque and reflect light well. You’ll find submetallic luster in the thin splinter sections of minerals, such as sphalerite, cinnabar, and cuprite.
• Vitreous or glassy luster describes 70% of all minerals, and they have the luster of glass. Quartz, calcite, topaz, beryl, tourmaline, and fluorite are examples of glassy luster.
• Adamantine lusters (brilliant, like a cut diamond) are for transparent materials that show a very bright shine because they have a high refractive index.
• Resinous lusters are usually yellow, orange, or brown minerals that have high refractive indices (like the way sunlight goes through honey).
• Silky lusters have very fine fibers aligned in parallel, so it looks like a cloth of silk. Minerals like asbestos, ulexite, and a variety of gypsum called satin spar all have silky luster. If a sample has fibrous luster, it is coarser than a silky luster.
• Pearly luster minerals look like the way light reflects off pearls, like the inside an oyster shell. These types of minerals have perfect cleavage, like muscovite and stilbite. Mica also has a pearly luster. Some pearly luster minerals also have an iridescent hue.
• Greasy or oily luster looks like fat, and is found in minerals that have a lot of microscopic inclusions, like opal and cordierite. Most greasy luster minerals also feel oily.
• Pitchy luster looks a lot like tar, and is found in radioactive minerals.
• Waxy luster resembles wax, the way jade and chalcedony look on their surface.
• Dull or earthy luster minerals have very little or no luster at all, because they have a surface that scatters the light in all directions, like with Kaolinite. Some geologists say that earthy luster means less luster than dull, but it’s really a close call between the two.

When light strikes a surface, it can be reflected off the surface, like a mirror, or it can pass through, like a window, or both. Metallic luster has most of the light bouncing off the surface, whereas calcite has most passing through the mineral. When light travels through a mineral, it refracts, or changes speed, as it crosses the new material boundary. This is what makes the luster appear different for different materials.

Refraction is how light bends when it travels from one substance to another. When light moves through a prism, it bends, and the amount that it bends is seen as color that comes out the other side. Each color represents a different amount of bending that it went through as it traveled through the prism.

1. Label and number each of your samples and record this on your data table.
2. Hold your mineral in the sunlight.
3. Use the list to find the word that best describes what you see. Look particularly on your sample for a surface that is clean and not tarnished, discolored, or coated. Look at cleaved surfaces and on uneven parts.

• Metallic
• Submetallic (duller than metallic)
• Vitreous or glassy
• Adamantine (like a cut diamond)
• Resinous (like honey)
• Silky (like a silk cloth)

• Pearly
• Greasy or oily
• Pitchy (like tar)
• Waxy (like a candle)
• Dull or earthy

4. Record your observations in the data table.

Exercises

1. What is refraction?
2. Feldspar has perfect cleavage on two surfaces but fractured on a third. What kind of luster would you say it has?
3. What type of luster is found on mica?

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Tenacity is a measure of how resistive a mineral is to breaking, bending, or being crushed. When you exceed that limit, fracture is how the mineral breaks once the tenacity (or tenacious) limit has been exceeded.

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Materials

• Hammer (if your piece of coal is large)
• Rock samples (in the video: copper, mica, selenite, sulfur)

Download worksheet and exercises

Tenacity is a measure of how a mineral behaves when under stress, like being crushed, bent, torn, or hammered. Minerals will react differently to each type of stress. Minerals can have more than one type of tenacity, since it’s possible for a mineral to have different (or several at the same time) reactions to the stress. Here’s a way to classify their response to stress:

• Brittle: The sample crumbles or turns into a powder. Most minerals are brittle, like quartz.
• Sectile: These minerals can be separated with a knife, like wax, like gypsum.
• Malleable: When you hammer the mineral and it flattens instead of breaks, it’s malleable like silver and copper.
• Ductile: A mineral that can be stretched into a wire is called ductile. All true metals are ductile, like copper and gold.
• Flexible-Inelastic: When you bend a mineral and release it, it stays in the new shape. It was flexible enough to bend, but it didn’t snap back into its original shape when released, like copper.
• Flexible-Elastic: When you bend a mineral and release it, it springs back into its original shape. Minerals that are flexible-elastic are fibrous, like chrysotile serpentine.

1. Label and number each of your samples with your data table.
2. Use a hammer and try to break the copper sample. Make sure you do this on a hard surface (like the concrete) so you don’t damage your floor or table!
3. To test for brittleness, like for sulfur, do a scratch test to see if it leaves a fine powder. Use your streak plate if you think your specimen has a hardness of less than 7.
4. For sectile tenacity, like with mica, carefully insert a knife into the mineral to see if it goes through. If the knife can penetrate through the sample (be careful with this!), then it’s sectile.
5. To check for flexibility, like mica and selenite, use only slight pressure so you don’t break your sample. Notice if the sample springs back or retains its new shape when released.
6. Complete the data table with your observations.

Exercises

1. What are four different types of tenacity?
2. How is elastic different from inelastic tenacity?
3. How many types of tenacity can a mineral have?

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By the end of this lab, you will be able to line up rocks according to how hard they are by using a specific scale. The scale goes from 1 to 10, with 10 being the hardest minerals.
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Materials

• Steel nail
• Penny
• Small plate of glass (optional)
• Rock samples (minerals in the video: talc, selenite, calcite, fluorite, apatite, feldspar, quartz)

Download worksheet and exercises

The sample’s hardness is determined by trying to scratch and be scratched by known materials, like pennies, steel, glass, and so forth. If the material leaves a mark on the mineral, then we know that the material is harder than the mineral is. We first start with a fingernail since it’s easy to use and very accessible. If it leaves a mark, that means that your fingernail is harder than the mineral and you know it’s pretty soft. Talc is one of the softest minerals, making it easy to scratch with your fingernail.

However, most minerals can’t be scratched with a fingernail, so we can try other objects, like copper pennies (which have a hardness of 2.5-3.5), steel nail (3.5-5.5), steel knife (5.5), and even quartz (7). The most difficult part of this experiment is keeping track of everything, so it’s a great opportunity to practice going slowly and recording your observations for each sample as you go along.

1. Number your samples on the data table and place each rock on the table. If you have the same samples listed above, you can scratch each rock with every other rock to find where they are on the Mohs’ Hardness Scale, where 1 is the softest and 10 is the hardest:
   Mohs’ Scale of Hardness Talc
   
   
   1. Selenite
   2. Calcite
   3. Fluorite
   4. Apatite
   5. Feldspar
   6. Quartz
   7. Topaz
   8. Corundum
   9. Diamond
2. If you don’t have one of each from the following scale (at least up to quartz), then you’ll need to do this experiment a different way – the way most geologists do it in the field. Here’s how:
3. Scratch one of the rocks with your fingernail. If you can leave a mark, then write “Y” in the second column of the data table. Now skip over to the last column and estimate the hardness to be less than 2.5.
4. If you can’t scratch it with your fingernail, try using the mineral to scratch a copper penny. If it doesn’t leave a mark on the penny, skip over to the last column and estimate the hardness to be between 2.5-3.5.
5. If it does leave a scratch on the penny, then try scratching the mineral with a steel nail. If the nail leaves a scratch, skip over to the last column and estimate the hardness between 3.5-5.5.
6. If you can’t scratch the sample with the nail, see if the mineral can make a scratch on the plate glass. Glass has a hardness of 6-7. If it doesn’t make a scratch on the glass, then it’s between 5.5-6.5. If it does, it’s higher than 6.5. For example quartz will make a scratch on the plate, and its hardness has been recorded at 7.

Exercises

1. If a mineral scratches a penny but doesn’t get scratched by a nail, can you approximate its hardness?
2. Give examples of the hardest and softest minerals on the Mohs’ Scale.
3. Is feldspar harder or softer than quartz?

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You will be able to identify minerals by their colors and streaks, and be able to tell a sample of real gold from the fake look-alike called pyrite.

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Materials

• 1 handheld magnifying lens
• Unglazed porcelain tile
• Rock samples (the ones in the video are: graphite, pyrite, talc, iron, and jasper)

Download worksheet and exercises

Every mineral has a set of unique characteristics that geologists use to test and identify them. Some of those tests include looking at the color of the surface, seeing if the mineral is attracted to a magnet, dripping weak acids on the rock to see if they chemically react, exposing them to different wavelengths of light to see how they respond, scratching the rocks with different kinds of materials to see which is harder, and many more. There are more than 2,000 different types of minerals and each is unique. Some are very hard like diamonds, others come in every color of the rainbow, like quartz and calcite, and others are very brittle like sulfur.

The color test is as simple as it sounds: Geologists look at the color and record it along with the identification number they’ve assigned to their mineral or rock. They also note if the color comes off in their hands (like hematite). This works well for minerals that are all one color, but it’s tricky for multi-colored minerals. For example, azurite is always blue no matter where you look. But quartz can be colorless, purple, rose, smoky, milky, and citrine (yellow).

Also, some minerals look different on the surface, but are really the same chemical composition. For example, calcite comes in many different colors, so surface color isn’t always the best way to tell which mineral is which. So geologists also use a “streak test”.

For a streak test, a mineral is used like a pencil and scratched across the surface of a ceramic tile (called a streak plate). The mineral makes a color that is unique for that mineral. For example, pink calcite and white calcite both leave the same color streak, as does hematite that comes in metallic silvery gray color and also deep red. This works because when the mineral, when scratched, is ground into a powder. All varieties of a given mineral have the same color streak, even if their surface colors vary. For example, hematite exists in two very different colors when dug up, but both varieties will leave a red streak. Pyrite, which looks a lot like real gold, leaves a black streak, while gold will leave a golden streak.

The tile is rough, hard, and white so it shows colors well. However, some minerals are harder than the mineral plate, like quartz and topaz, and you’ll just get a scratch on the plate, not a streak.

1. Number your rock samples by placing them on your data table.
2. Using your data table, record the color of each sample.
3. Now use your streak plate. Take a rock and draw a short line across your streak plate (unglazed porcelain tile).
4. Record the color of the streak in your data table. Are there any surprises?

Exercises

1. What does it mean if there’s no streak left?
2. Give an example of a kind of rock that leaves a streak a different color than its surface color.
3. What is a mineral that appears in two different colors, yet leaves the same color streak?

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