Download Instructions / Assembly

WHAT’S IN YOUR KIT
Packet of Rocks-Bag of Sand - Magnifying Lens
- Rock Display Card
IMPORTANT: Adult Supervision
In this book, this symbol indicates an activity that
should be performed under the supervision of an
adult. It involves heat, or the use of chemicals, or
extreme messiness.
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INTRODUCTION
What we think of as the surface of the Earth is part of what geologists call the crust. It is made up of the continents and the ocean
floor. Like the skin on a peach, it is just one layer, different from
the layers that lie beneath it.
The Earth is constantly swallowing old rock and bringing new rock
to the surface. But what is rock, anyway? What are rocks made of?
Why are there different kinds of rocks?
In this kit, you’ll find some of the answers. You’ll find out how
rocks are made, how they are destroyed, and how the pieces are
recycled. And in addition, you will- Smash one of the toughest rocks in the world with a few light
taps of a hammer.
- Create a rock of your own out of sand and sugar.
- Make carbon dioxide gas bubble out of a rock.
- Start a rock collection that includes
- a rock that floats on water
- a rock squeezed up from the Earth’s mantle, a layer of the Earth hundreds of miles deep.
- a hard rock made from soft mud
and more!
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1. IGNEOUS ROCKS I - ROCKS MADE FROM MAGMA
All the rocks on earth originated from magma - liquid rock from
deep underground. Either they formed directly from magma, or are
made from rocks that cooled from magma.
Rocks formed directly from magma and lava (what magma becomes
when it comes out from the ground) are called igneous (IG-nee-us)
rocks - meaning “rocks formed by fire”. Igneous rocks form more
than 65% of Earth’s crust. Your packet of rocks contains four
different kinds of igneous rocks.
BASALT
Basalt (ba-SALT) is the most common kind of igneous rock in
Earth’s crust. It is the rock of the ocean floor, formed from lava that
poured out of spreading ridges under the sea. It is also the lava rock
produced by many famous volcanoes and lava flows. The great lava
flows of Iceland and Hawaii are basalt. So are the monster lava flows
that covered much of India 65 million years ago. Much of the eastern
part of the states of Washington and Oregon is covered with layers of
basalt hundreds of feet thick, laid down in other monster lava flows
about 17 million years ago. When Earth scientists add it all up, they
find that basalt and similar rocks make up about 43% of all the rocks
in the Earth’s crust.
Not all basalt comes out of a volcano. Sometimes rising lava forces
its way into cracks in the rocks not very far underground. It cools
there, forming a basalt sandwich called a sill between layers of the
original rock. When the top layer of rock wears over millions of
years, the basalt comes to the surface. The famous Hudson River
Palisades, a line of cliffs up to 800 feet (244 m) high that overlooks
New York City, is an ancient basalt sill formed this way. It was
formed 200 million years ago.
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Basalt is a tough, hard rock, very resistant to weathering. It’s not
used much in buildings, but is often crushed into small stones that
are used to pave roads and to support railroad tracks.
Activity 1 - IDENTIFY BASALT FROM YOUR ROCK COLLECTION
You need from your kit: The Rocks Packet
1. Look at your rocks. Two of them are dark gray, with no speckles, or
streaks, or bands. One dark gray rock is flat and smooth. The other is just an
irregular chunk of rock. The second one is basalt.
GRANITE
Granite (GRAN-it) is the other common kind of igneous rock. It is
the main rock of the continents, just as basalt is the rock of the sea
floor. About 22% of Earth’s crust is made of granite or some similar
rock.
Granite is an igneous rock, but it is not a lava rock. Lava flows on or
near the earth’s surface, but granite never does. It forms deep below
the surface of the continents, when a huge mass of magma rises
into the continental crust and cools there over millions of years. If a
period of mountain building then occurs, the granite may be thrust
upwards. It will appear at the surface millions of years later when all
the rock that once covered it has worn away.
No one who has ever tried to lift a large slab of granite will believe
this, but granite is actually a fairly light rock. It’s lighter than basalt, and it “floats” on heavier rocks like the rock that makes up the
mantle. Billions of years ago, when the crust of the earth was forming, granite floated on top of the rock of the mantle in clumps that
gradually grew and stuck to each other. That ancient granite forms
the cores of the continents today. It is much older than basalt. The
oldest basalt on the ocean floor is only about 200 million years old.
But the oldest granite, at the heart of the continents, is nearly 4
billion years old!
Not all granite is that ancient. Rock deep inside the continents can
still melt and cool again to form new granite. You can see granite
formed this way right next to the great basalt flows of Eastern Washington and Oregon, in the mountains of Idaho and western Montana.
About 70 million years ago, melted continental crust formed a
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granite magma, which melted its way up through the solid crust
above it. About 10 miles (16 km) below the surface, the magma became a mass of solid granite and started to cool. But it took millions
of years - and the removal of 10 miles (16 km) of rock on top of it before the granite saw the surface.
Activity 2 - IDENTIFY GRANITE FROM YOUR ROCK COLLECTION
You need from your kit: The Rocks Packet
1. Look at your rocks. Two of them look alike: reddish or pinkish tan, with
large speckles of gray and black, but no streaks or bands. These two rocks are
granite.
Granite, with its speckles of gray, pink, and black, is actually a very
attractive looking rock. Builders often cut it into slabs and columns
and polish it until it becomes as smooth as glass. You’ll often find
polished granite used for the sides and the floors of important buildings like banks or courthouses. Some people use it for kitchen counters, because it is so hard and does not stain.
OLIVINE
Olivine (AH-liv-een) is not a common igneous rock - at least not on
the surface of the Earth. Actually, olivine is not a crustal rock at all.
It is the rock of the mantle, the layer of the Earth below the crust.
Since the mantle extends down for hundreds of miles (km), olivine is
probably Earth’s most common rock.
Activity 3 - IDENTIFY OLIVINE FROM YOUR ROCK COLLECTIONYou need from your kit: The Rocks Packet
1. Look at your rocks. One of them is a light yellow-green color. This rock is
olivine.
PUMICE
Pumice (PUM-iss) is one of the strangest and most interesting of
all igneous rocks. It is a rock foam, formed from a thick and gummy
volcano lava that is chemically similar to granite but that is also rich
in gases. When the volcano erupts, it blasts globs of this lava high
into the air, where they solidify and fall back on earth. The trapped
gas forms tiny bubbles in the lava, so that the lava ends up with more
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gas than rock! The sample in your packet may be as much as 85%
bubbles and only 15% rock.
Pumice is used as a grinding material, like sandpaper. Its big advantages is that it has no sharp, rough edges to damage delicate surfaces.
People sometimes use it in the bath to smooth rough patches on their
skin.
Activity 4 - IDENTIFY PUMICE FROM YOUR ROCK COLLECTIONYou need from your kit: The Rocks Packet
You also need: a glass of water.
1. Empty all the rocks in your packet into the glass of water.
2. Pick out the pumice. It’s the rock that floats!
HOW CAN YOU TELL WHERE A ROCK WAS FORMED?
Rocks differ from each other in two basic ways:
- They differ in what they are made of - in their chemistry.
- And they differ in the way they are formed.
Basalt and granite are good examples of these two kinds of
differences.
- They are chemically different. (However, you have to know some
chemistry or geology to know how they are different.)
- And they were formed in different ways - one above ground and
the other deep underground. You can actually see this difference.
Here’s how:
Like all rocks, basalt and granite are mixtures of several different
minerals. When magma or lava cools and becomes a solid rock, the
individual minerals form distinct grains called crystals.
As you will see in later activity, it takes time to form good crystals.
In general, the longer the cooling period, the larger the crystal.
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When melted rock is thrown out into the air, it cools fast - too fast to
form large crystals. When it sits cooling underground for a million
years or so, it has all the time it needs. So the different way they are
formed makes a difference in crystal size.
In the next activity, you will compare crystal sizes in a rock that
cooled above ground and a rock that cooled deep underground.
Activity 5 - COMPARE CRYSTAL SIZE IN GRANITE AND BASALT
You need from your kit: The granite and the basalt-the magnifying lens.
1.Look closely at the basalt in bright light. Can you see individual crystals?
They are usually almost impossible to see without the help of a magnifying
glass or a microscope. Tilt the basalt slowly from side to side. You may be able
to see tiny sparkles from the crystal surfaces. Very tiny crystals are one sign of
a rock that cooled on (or near) the surface of the earth.
2. Now look at the granite. You can easily see many crystals of different sizes
and colors. This is the sign of a rock that cooled deep underground.
2. IGNEOUS ROCKS II - THE MINERALS IN AN IGNEOUS
ROCK
WHAT IS A MINERAL?
In the last activity, you examined the rock granite. And you saw that
a rock is not a single substance. It is a mixture of several different
substances, or minerals. But just what is a mineral?
It’s easier to start with an example than a definition. Salt is a mineral. Ordinary table salt.
Let’s see what makes a salt a mineral.
- First, salt is a naturally occuring substance. People dig for it in salt
mines.
- Second, salt is a single substance. It’s not a mixture of several
things. Salt is salt.
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A mineral like salt may have two names - a mineral name and a
chemical name.
- The mineral name is what an earth scientist calls the mineral. If
you look up salt in a book of minerals, you’ll find it called halite
(HAY-lite). In the winter, hardware stores sell rock salt to melt ice,
and the label on the bag often uses the mineral name halite.
- The chemical name gives a clue as to what kinds of atoms make
up the mineral. Salt, for example, is sodium chloride. It is made of
atoms of sodium and chlorine.
(A bit of chemistry here-sodium is a soft, silvery metal that explodes
and burns when it comes in contact with water. Chlorine is a greenish poison gas. It is one of the miracles of chemistry that these two
substances-either of which would kill you if you ate it or breathed itcombine to form a completely new substance that you must have in
your body to stay alive! This is why salt is called a compound, not a
mixture. When the substances that make a compound combine with
each other, they make something completely different. In a mixture,
like a rock, they don’t. They just sit side by side and don’t react with
each other at all.)
MINERAL CRYSTALS AND ROCKS
The atoms in a mineral usually have a definite, regular arrangement.
The atoms in salt, for example, arrange themselves to form a cube.
This regular arrangement gives a distinctive shape to a mineral
crystal.
Crystals of a mineral grow. They do this by attracting more of the
atoms they are made of. This is easiest when they are surrounded
by a liquid containing the neccesary atoms. So crystals of a mineral
form and grow best in water containing the dissolved mineral-or in
liquid magma.
Crystals tend to grow in a particular regular shape. But in a cooling
magma, the crystals of the different minerals interlock as they grow.
They end up in a mishmash of irregular interlocking crystals- a rock.
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Earth scientists know of about 3000 different minerals, and new
ones are discovered every year. But only a few minerals are common
enough to make rocks.
Activity 6 - IDENTIFY 3 MINERALS IN GRANITE
You need from your kit: The granite and the magnifying lens.
1.Take a close look at one of your pieces of granite. You should be able to see
at least three of the minerals that make up the rock:
- A glassy gray mineral
- A light, pinkish-tan mineral
- Specks of a black mineral
You may be able to pick out other minerals as well, but these three are the
main ones.
QUARTZ-A SILICATE MINERAL
The glassy gray mineral in granite is called quartz (KWORTS).
Quartz is one of the most common materials of the Earth’s crust. In
its pure form, it is clear, hard crystals with pointy ends. Tiny amounts
of other materials may color it a beautiful golden yellow, smoky gray,
purple, or other colors.
Quartz is one of the most useful of all minerals. A tiny quartz crystal
keeps time in modern wristwatches and clocks. Melted and mixed with
other minerlas, quartz is the principal ingredient in glass. Purple quartz
is the gemstone amethyst (AM-a-thist).
Chemically, quartz is a member of an important group of about 500
minerals called silicates. Nearly all rock-forming minerals are silicates. Silicate minerals contain two kinds of atoms-atoms of silicon
and atoms of oxygen. Quartz is the simplest silicate. It contains just the
two kinds of atoms.
- By itself, silicon is a grayish substance that is almost but not quite
a metal. You have probably never seen it, but your life would be very
different without it. It is the material that computer chips are made of.
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- Oxygen is the gas that your body uses when you breathe.
Neither substance is the slightest bit like quartz. But combine
silicon and oxygen chemically, and the usual miracle happens. You
get something completely different-a hard, transparent mineral like a
chunk of unbreakable glass.
QUARTZ AND LAVA
The presence of quartz is one of the big differences between granite
and basalt. Basalt contains lots of other silicate minerals, but very
little quartz. Granite, on the other hand, is between 20% and 60%
quartz.
Granite, as you know, forms deep underground. But sometimes a
granite-type magma, containing lots of melted quartz, reaches the
surface of the earth and forms a volcano. The lava rock that it makes
is very different from basalt. It is light-colored rock called rhyolite
(RIE-o-lite). Rhyolite contains the same minerals as granite. But like
basalt, it has only very tiny crystals.
Quartz makes a lava thick, pasty, and gummy. It doesn’t flow
smoothly like a basalt lava. Rhyolite volcanoes can be terribly dangerous, especially if the lava contains large amounts of gas. Then
they are explosive. The yellow rock that gives Yellowstone National
Park its name is rhyolite.
When rhyolite cools very quickly, it doesn’t form crystals at all. It
becomes a glass, usually black, called obsidian (ub-SID-ee-un).
Have you ever cut yourself on broken glass? You can do the same
thing with obsidian. Indian people used it to make sharp spear points
and arrowheads. In Mexico, the Aztec Indians stuck razor-sharp
chunks of obsidian into the edges of a flat wooden club, making a
truly terrible weapon.
One of the samples from your rock packet that you have already
examined is a rhyolite glass foam. It’s pumice.
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FELDSPAR
The pink-tan mineral in granite is one of a group of similar silicate
minerals called feldspars.
Feldspars are among the most common minerals in Earth’s crust. A
little more than half of the crust is composed of different kinds of
feldspars.
Feldspars are widely used. The scouring powder in your kitchen may
contain finely ground feldspar. The porcelain sink or toilet that it
cleans is also made from feldspar, plus quartz and clay.
Chemically, feldspars are cousins of quartz. Like quartz, they contain
atoms of silicon and oxygen. They are therefore silicate minerals,
but they also contain atoms of aluminum.
MICA
The black mineral in granite is called mica (MIKE-a). Mica comes
in flat sheets that easily split off from one another.
Other kinds of mica are golden, and some are even transparent.
Before the invention of heat-resistant glass, clear mica was used in
stoves to make heat-proof oven windows.
Unlike quartz and feldspar, black mica is not used to make anything.
The problem is that it contains iron. Mica without iron is a good
electrical insulator. It is often turned into a kind of mica paper made
from powdered mica held together with plastic. But mica containing
iron, will conduct some electricity. It cannot be used as an insulator.
Chemically, mica is a silicate mineral like feldspar, but a very complicated one. In addition to containing all the kinds of atoms that
feldspar has, it also contain atoms of iron, magnesium, hydrogen,
and flourine.
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3. IGNEOUS ROCKS III - THE BREAKDOWN OF AN
IGNEOUS ROCK
BREAKING DOWN GRANITE
On Earth, nothing lasts forever. Even granite, the symbol of permanence, breaks down with time. Here’s how you can speed up the
process in your kitchen.
Activity 7 - BREAK DOWN GRANITE BY WEATHERING
You need from your kit: One of the two pieces of granite.
You also need: An oven, a sheet of aluminum foil, tongs, a pot holder, some
paper towels, a pan of ice water, and a free two hours. This experiment takes
about two hours to do.
1.Wrap the piece of granite in the paper towel and hit it a few times with the
hammer. Use about the same force you would use to drive an ordinary nail.
The granite will not break. (If it does break, it either had a crack in it or you
are hitting too hard.)
2. Preheat an oven to 400 degrees F (200 degrees C).
3. Place the pan of ice water in the freezer of your refrigerator to keep cold.
4. Place the granite in the oven on the sheet of foil. Remember to remove the
paper towel! Keep it there for 15 minutes.
5. Remove the granite carefully, using tongs and the pot holder, and drop it in
the pan of ice water. Keep it there for 1 minute.
6. Put the granite back in the oven, and repeat Steps 3-5 seven or eight times.
7. Wrap the granite in a paper towel and hit it several times with the hammer
the way you did before. With only a few medium-hard taps, you should now be
able to break it into small pieces of the minerals it is made of.
8. Remember to turn off the oven!
Activity 8 - SORT GRANITE PARTICLES INTO MINERAL GROUPS
You need from your kit: The particles of granite from the previous activity,
the magnifying lens
You also need: A sheet of white paper.
1.Brush the granite particles onto the paper. Set the paper on a clean, flat, dry
surface, like a kitchen counter.
2. Look at the particles carefully. Most of them are grains of single minerals,
showing that the granite broke between the crystals.
3. Try to sort some of the particles into three groups: quartz, feldspar, and
mica. You will probably be able to pick out a few crystals of quartz and feldspar, plus some specks of mica.
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This experiment shows you two of the things that break down granite:
heat and cold. Heat makes the crystals in the rock expand, and cold
shrinks them. Hammers do not occur in nature, but ice does, and it
splits rock just as effectively as a hammer. This is because water expands as it freezes, cracking even granite.
The natural breakdown of rock that you imitated is called weathering.
The grains of rock are eventually transported by water or wind to a
resting place far from the original rock. The combination of weathering and transport, which break down rock and removes the pieces, is
known as erosion.
This is the way all rocks at the surface of Earth come to an end. Over
millions of years, they are broken down into small particles by erosion.
In the next section, however, you will see how these particles can get
another chance at becoming a rock.
4. SEDIMENTARY ROCKS I - NEW ROCKS FROM OLD
BREAKING DOWN GRANITE
The small particles removed from a rock by erosion do not just go
away. On Earth, there is no “away”. Here are some of the things that
happen to particles eroded from granite:
- Medium-sized particles of quartz become sand.
- Small feldspar and mica particles may react chemically with water to
form new minerals. Clay is made out of these minerals.
- Some of the particles may mix with decaying plants to form soil.
- The smallest particles may become dust, and get blown away by the
wind. They may end up as part of the soil hundreds of miles away.
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- A stream may carry some particles into a river, and the river may
carry them out to sea. There they can pile up in layers whose thickness
can be measured in miles or kilometers.
- Some of the particles actually dissolve in water.
SEDIMENT AND SEDIMENTARY ROCK
Earth scientists use a single word to describe particles eroded from
rock: sediment.
Over millions of years, sediment transported from weathered rock piles
up in layers thousands of feet deep. Some of it is on land. Most of the
land between the Mississippi River and the Rocky Mountains is made
up of sediments eroded from the Rockies. At the foot of the Rockies,
the sediments are a mile thick. Parts of the Rio Grande Rift are filled
with sediments to a depth of nearly 6 miles ( 9.6 km). In the ocean near
the shores of the continents, sediments are piling up to similar depths.
As the sediments pile up, the layers are squeezed together. The particles are pressed close to each other. Water with dissolved minerals
like quartz flows through the spaces between the particles, and some of
the minerals come out of the water to form a sort of cement that glues
the particles together. Eventually, all the particles are sqeezed and
cemented together to form a new rock-a rock made from sediments, or
sedimentary rock.
Sedimentary rock makes up only about 6% of the continental crust.
But it forms at the top of the crust, and covers the igneous rock below
it. Most of the surface of the continent is sedimentary rock.
SANDSTONE
One of the best known of all sedimentary rocks is sandstone, made
mostly from small particles of quartz. The famous red rocks of the
U.S. Southwest, featured in so many TV car commercials and Western
movies, are made of sandstone. Its grains eroded from long-vanished
western mountains 200 million years ago. You have a piece of this rock
in your rock packet.
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Activity 9 - IDENTIFY SANDSTONE FROM YOUR ROCK
COLLECTION
You need from your kit: The Rocks Packet
1.Look at your rocks. One of them is an even reddish-brown color. This is
sandstone.
2. Rub your fingertip across it. It should feel like a kind of rock sandpaper.
3. Scratch it with a coin or a key. You should be able to scratch some of the
sand grains off it.
Here are some things to notice:
-The red color of your sandstone comes from tiny amounts of a reddish
mineral called hematite (HEE-ma-tite).
- This particular rock didn’t form underwater. It is made from ancient
desert sands.
-The sandstone in your kit is from the state of Colorado. In Spanish,
the word colorado is one of the words for “red”. Now you know what
gave the state its name.
- Incidentally, the word sandstone is one of the few places where you
will find an earth scientist using the word stone. For some reason,
they generally use only the word rock. Builders and masons say stone;
scientists say rock. Then they forget their own rule and come up with
names like sandstone, mudstone, soapstone, and gritstone.
Nature made the sandstone in your kit, and took millions of years to do
it. But you can make a chunk of sandstone in a few minutes. The next
activity will show you how.
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Activity 10 - MAKE SANDSTONE FROM SAND AND
SUGAR
You need from your kit: The packet of reddish-brown sand.
You also need: Sugar, water, measuring spoons, a microwave
oven, a small dish that can be used in a microwave oven, a pot
holder and the freezing compartment of your refrigerator.
1. Pour out the sand into the dish. Add 1 tablespoon of sugar
and 1 tablespoon of water and mix.
2. Microwave on high for 1 1/2 minutes.
3. Take the dish out of the oven. Stir the mixture with a spoon
until it starts to get sticky and hard. Then, when it is cooled,
mold it with your fingers into the shape of a rock.
4. Place it in the freezer for about 5 minutes. Then take it out.
5. Use hot water to clean everything up.
- The sand in your sandstone is being held together by a cement made
of crystals of heated sugar. It may be sticky, so don’t put it on cloth or
wood furniture.
- Of course, your sandstone will fall apart in a couple of minutes if
placed in water.
5. SEDIMENTARY ROCKS II - A NEW KIND OF ROCK, A
NEW KIND OF MINERAL
LIMESTONE-A DIFFERENT KIND OF SEDIMENTARY ROCK
Even more common than sandstone is the sedimentary rock known as
limestone. Limestone forms underwater, like most sedimentary rock,
but it is also found nearly everywhere on land. Most of Earth’s land
surface has been underwater at one time or another, and limestone
formed on it at that time. Continental collisions can also lift up layers
of ocean limestone and make them the tops of mountains. The peak of
Mount Everest, the highest mountain in the world, is limestone. As a
result, although limestone and similar rocks make up only about 4% by
weight of Earth’s crust, they cover 40% of its surface.
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Unlike the rocks you have identified so far, limestone is not made of
silicate minerals. Much of it consists of broken-up and packed-down
sea shells-not just snail and clam shells, but also the “skeletons” of
corals and the tiny shells that wrap around certain one-celled ocean
creatures. It is amazing that a rock that covers nearly half the Earth
was largely created by living things.
Seashells are made of a chemical named calcium carbonate, so limestone is considered a carbonate rock.
Activity 11 - IDENTIFY LIMESTONE FROM YOUR ROCK
COLLECTION
You need from your kit: The Rocks Packet
1.Look at your rocks. Two of them are light gray. This is limestone. The following tests as well as the test in Activity 12 will show you how to be sure.
2. Scratch the limestone with a coin or a key. You should be able to make a
whitish scratch on it, even though the rock isn’t white.
3. Bring your limestone near a bright light, or hold it in the sunlight. Tilt it and
turn it, very slowly. You should be able to see, here and there, little pinpoint
sparkles of light from the mineral crystals in the rock.
4. Wet the piece of limestone and rub it against a piece of granite. Then smell
it. The smell is the smell of limestone. (If you’ve ever smelled wet chalk, you
are already familiar with the smell. Chalk is a kind of very soft limestone.)
- Limestone is not always gray. It can be white, or black, or even
reddish.
Activity 12 - TEST THE LIMESTONE WITH VINEGAR
You need from your kit: The limestone you identified in Activity 11.
You also need: Vinegar and a small dish.
1.Place your piece of limestone into a dish and cover it with vinegar. Watch it
carefully. You should soon see tiny bubbles covering it, and bubbling up to the
surface of the vinegar.
2. If you leave the limestone in the vinegar for a long time, bits of the stone
will fall off. The acid in the vinegar is slowly eating the limestone away.
Here are some things you should know about this test for limestone.
- This test with vinegar is a standard test for limestone. A chunk of
gray limestone can look like a lot of other rocks, but if it bubbles in
vinegar, it’s almost certainly limestone.
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- the bubbles that come off the limestone are carbon dioxide gas.
That’s the same gas that makes bubbles in soda pop.
- Earth scientists use a stronger acid for this test, so the limestone will
bubble faster. Vinegar is a weak acid. But even a weak acid eats away
at limestone.
- Some of the world’s most famous buildings and statues are made of
limestone. And a lot of the world’s raindrops are weak acid. What do
you think acid rain is doing to limestone buildings and statues?
CALCITE-THE CARBONATE MINERAL OF LIMESTONE
Unlike most rocks, limestone is composed mostly of a single mineral,
calcite (KAL-site). Calcite is a whitish or clear mineral like quartz,
but it is much softer. It is calcium carbonate, the material of which
seashells are made. Pure crystal calcite can have many different colors
and shapes.
6. SEDIMENTARY ROCKS III - MINERALS AND CRYSTALS
FROM WATER
GROWING MINERAL CRYSTALS
Water dissolves salt. It also dissolves sugar. Give it enough time, and it
will dissolve quartz, feldspar, mica, and other minerals as well.
Hot water dissolves things much better than cold water does. When
water moves through the cracks of cooling magma and lava, it gets
very hot, and it dissolves many minerals. When the water flows to a
cooler crack in the rocks, it cools and lets go of the dissolved minerals.
Mineral crystals and mineral deposits build up in the crack. (A crack in
a rock with a mineral deposit is called a vein.)
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Activity 13 - MAKE CRYSTAL CANDY
You need: Sugar, 1 cup, water, 1/2 cup, a saucepan, a drinking
glass, a pencil, wax paper, a piece of thread and a paper clip
1. Pour the water in the saucepan and bring it to a boil. Then turn
down the flame.
2. Add sugar and stir. Keep adding sugar and stirring until no more
sugar will dissolve.
3. Pour the solution into a glass.
4. Tie a small paper clip to the end of a thread. Tie the other end of
the thread around the middle of a pencil.
5. Dip thread in solution, lay on wax paper straight and let dry
overnight. Tiny crystals will form overnight that larger crystals
will grow on.
6. Rest the pencil like a bridge across the glass, so that the thread
and the paper clip hang down in the solution without touching the
bottom or the sides.
6. Leave uncovered in a safe place. Do not disturb! In about a
week, your sugar crystals will be ready to eat. This kind of candy
is sometimes called rock candy.
7. METAMORPHIC ROCKS - ROCKS CHANGED BY
HEAT AND PRESSURE
The crust is really a giant, slow-acting chemistry set. Minerals are the
chemicals, and they are mixed together to form rocks. Under great
heat, great pressure, and great amounts of time, the minerals react
chemically with each other. They change into other minerals and the
rocks change into other kinds of rocks.
Rock change from pressure and heat is called metamorphism (METa-MOR-fism), and it makes a kind of rock called metamorphic
(MET-a-MOR-fic) rock. The word metamorphic means something like
“changed all through”-a good description of what has happened to the
original rock.
Metamorphic rocks can form out of igneous rocks, sedimentary rocks,
and even other metamorphic rocks. All it takes is enough heat, and
enough pressure, and enough time.
ROCKS CHANGED BY BEING NEAR MAGMA
Liquid rock, heated to more than a thousand degrees, pushes up from
20 the depths of the Earth. It squeezes the surrounding rock and heats it
hundreds and even thousands of degrees. The minerals in the surrounding rock react with each other, and a metamorphic rock is born. What
kind it is depends on what kind of rock it changed from.
If the surrounding rock is limestone, not much chemical change is possible. Most of limestone is plain calcite. But the calcite crystals grow
larger, and any other minerals that happen to be in the rock react with
them. The new rock is harder than limestone, and it may be beautifully
colored and streaked with unusual patterns. It is called marble, and it is
widely used in buildings and for making statues. When you see polished stone with a pattern of streaks in it in a bank or a public building,
it is probably marble.
If the rock surrounding the magma is a sedimentary rock made from
mud or clay, a different metamorphic rock results. The heat from the
magma may change it into a tough, hard metamorphic rock called
slate. It doesn’t take as much heat to change mudstone or claystone
into slate as it does to change limestone into marble.
Activity 14 - IDENTIFY SLATE FROM YOUR ROCK COLLECTION
You need from your kit: The Rocks packet.
1.Look at your gray rocks. One of them is flat, an even dark gray, and looks
like it was formed in layers. This is slate.
Slate splits fairly easily into flat sheets. For this reason, it is widely
used to cover roofs. In older schools it used to be used for chalkboards,
and it is still sometimes used for kid’s slates you can buy in a toy store.
ROCKS CHANGED BY BEING SQUEEZED
When a region of rock is being squeezed into a mountain, or when it
has 30 or 40 miles of other rock sitting on top of it, tremendous pressures and heat result. These pressures can cause metamorphism, just as
contact with magma does.
Granite and sandstone are examples of rocks that can be changed this
way. Under tremendous pressure, their crystals re-form in streaks and
bands, and a metamorphic rock called gneiss (pronounced NICE) is
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formed. Gneiss is found at the heart of mountains like the Alps and the
Rockies, as well as in very ancient parts of continents.
Activity 15 - IDENTIFY GNEISS FROM YOUR ROCK COLLECTION
You need from your kit: The Rocks packet.
1.Look at your rocks. Find the one you have not identified yet. It has short, flat
streaks, bands, or lines through it. This is gneiss.
BACK TO IGNEOUS ROCKS
It takes very high pressure and temperature to make gneiss. What happens if a rock is squeezed and heated even more? It melts. It turns into
magma. And when it cools again, perhaps millions of years later, it is
no longer a metamorphic rock. It is an igneous rock, just like the rocks
we started with.
Activity 16 - MAKE A DISPLAY FOR YOUR ROCK COLLECTION
You need from your kit: The Rocks packet and display card.
You also need: Glue. Use rubber cement if you want to be able to remove your
rocks now and then. Use epoxy if you want your display to be permanent.
1 Glue each rock onto its proper square on the display.
ROCKS THAT PEOPLE MAKE
People make rocks the same way nature does. And the rocks they make
can be classed as igneous, sedimentary, or metamorphic, just like
natural rocks.
- Igneous Rocks. The commonest human-made igneous rock is ordinary glass. Glass is made by mixing quartz sand with other minerals
(washing soda, for example) and heating them until they melt. When
the mixture cools, it forms the human- made igneous rock we call glass.
- Sedimentary Rocks. If you completed Activity 10, you made sandstone, a sedimentary rock. Other, more useful human-made sedimentary rocks include concrete, plaster, and items like flowerpots that are
made of clay baked at low temperatures.
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- Metamorphic Rocks. When clay is heated to a very high temperature, it turns into a hard, rock-like substance made of interlocking mineral crystals-in effect, a metamorphic rock. Porcelain sinks and toilets
are made this way. So are china plates and dishes.
Activity 17 - IDENTIFY HUMAN-MADE IGNEOUS, SEDIMENTARY
AND METAMORPHIC ROCKS
You need: Stuff in your house and all around you.
1 Look around your home, or school, or neighborhood. How many humanmade “rocks” can you find? What class of rock does each one belong to?
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