Edible Igneous Rocks

(10 minutes)

D  Materials

1 12-ounce bag milk chocolate chips

1 12-ounce bag white chocolate chips

1 piece waxed paper (at least 18 x 24 inches/46 x 61 centimeters)

1 cookie sheet with sides

1 stirring spoon

heating device – microwave or double-boiler

microwave-safe bowl or double-boiler depending on heating method

rock samples from Unique Rock


D  What to Do:

1.       Review from Unique Rock that that the main way geologists classify rocks is by how they were formed. 

2.     Explain that igneous rocks are formed when melted rock, called magma, is forced up from the earth’s core through the earth’s surface and cools.  They are going to see a similar process when they make Edible Igneous Rocks.

3.     Place the white and milk chocolate chips in a bowl or pot.  Have the girls notice that there are individual pieces (chips), much like individual minerals in a rock.  Refer to rocks they have looked at in Unique Rock.

4.     Heat the chips until they melt.  Explain that this is similar to rocks melting in the high heat at the earth’s core.

5.     Mix well until all signs of individual chips is gone and the colors are completely blended.

6.     Show the children the bowl again.  Note that you can no longer see the individual chips and it is instead in a liquid mixed form.  This is similar to the liquid rock, called magma, in the earth’s core.

7.     Cover the cookie sheet with a sheet of wax paper.  As you pour the liquid chocolate onto the wax paper, tell the children that when there is a volcano the magma is forced through the earth’s surface and comes out as lava.  It then hardens as it cools and turns into igneous rock in the same way that the chocolate will harden as it cools.

8.     Set the chocolate aside to cool.  Caution everyone against touching the mixture, as it is very hot.

9.     Once the chocolate has cooled, break it up and notice that the new “rock” is made of the same ingredients, but is not like any of the original “rocks” which were melted and that none of these ingredients are visible anymore.  Eat and enjoy.


D  Helpful Hints

1.       Check for food allergies.

2.     Stir chips often and be careful not to burn the mixture.

3.     You can also sprinkle in some other kinds of chips (dark chocolate, butterscotch chips, peanut butter chips, marshmallows) in order to simulate the greater mixture of minerals in the magna and rocks.

4.     You can make a double boiler out of an electric hotpot of boiling water with a smaller saucepan sitting in the water.

5.     To speed the cooling process, put the mixture in the refrigerator for approximately 10 minutes.


D  Whys and Hows

          Igneous rocks are formed from melted rock that has cooled and hardened.  Rocks that are deep in the earth melt because of the high temperatures and the pressure.  The melted rock is called “magma.”  The magma is heated and forced up from the center of the earth through the earth’s crust.  Some of it comes out on the surface through a volcano as lava, and some of it stays underground where some will harden.  As it cools, the lava or magma hardens and turns into rock.  Therefore, The specific type of igneous rock formed depends on three things…how fast it cooled, where it cooled (outside of the earth’s surface, under the water, or under the earth’s surface) and what combination of chemicals was in the magma.  The slower a substance cools, the larger the crystals will be.  Thus, magma that cools more slowly, usually underground, will form larger crystals than those formed from the lava that is spewed out of a volcano and cooled rapidly.  Some examples of igneous rocks are granite (formed underground and cooled slowly, so there are visible crystals), obsidian (formed above the earth’s surface from lava hardened that hardened quickly), and pumice (formed from lava blasted out of a volcano into the air and cooled so fast that the gases were not able to escape, leaving lots of little holes in it).


D  Other Ideas to Explore

1.       Grow crystals to illustrate that slower growth of crystals leads to bigger crystals, as an example of why igneous rocks will be different depending on their cooling time.

2.     For a more involved and integrated geology-cooking project, follow the foolproof fudge recipe on the back of any marshmallow creme container.  This cooking is more involved, but a more dramatic simulation of different ingredients going in and coming out as one new conglomerate.


Sedimentary Sandwiches

(15 minutes)

D  Materials

Loaf of white bread

Loaf of brown bread

graham cracker crumbs

red jam

purple jam


crunchy peanut butter

15 plastic knives

15 paper plates

D  What to Do:

1.       Explain that sedimentary rocks are formed when layers of sand, small bits of rock, clay, plants, bones, and mud are piled on top of each other and eventually get compressed and harden into rock.  Sedimentary rocks are often formed in river bottoms and lakes since the water carries materials from other places that then settle to the bottom in layers.  This process takes a long time (hundreds of thousands of years).  They are going to see a similar model of this process when they make Sedimentary Sandwiches.

2.     Give each child a plate, explaining that it represents the bottom of a river.

3.     Show them the various materials to use as layers in their sedimentary rocks: white bread for white sand, brown bread for dust, peanut butter for mud, raisins for big rocks, red jam for old decaying plants, purple jam for old bones and remains of animals, and graham cracker crumbs for clay.

4.     Encourage the children to make their own sedimentary sandwich, thinking with each addition, what each layer represents.

5.     Explain that these layers get compressed, or smashed together, over time to become rock.  Suggest the girls press down on their sandwich to represent the compression of the layers.

6.     After they have made their sandwiches, have them make rock stories.

7.     Have them look at each other’s sandwiches and notice the variations.

8.     Also point out that when there is an earthquake or a mountain is formed, these layers are bent or broken.  Have the children bend their sandwiches and see what happens to the layers.


D  Helpful Hints

1.       Check for food allergies.  You can substitute cream cheese with fruit bits for the peanut butter if you have girls with peanut allergies.

2.     To make your own graham cracker crumbs put whole graham crackers in a sealed bag and roll with a rolling pin or hit with a hammer.

D  Whys and Hows

Sedimentary rocks are formed from particles or pieces of rocks that have been eroded away by wind, water or ice (see “Going, Going, Gone” for explanation of erosion) and deposited in layers.  These layers often form at the bottom of lakes or seas.  As the layers pile up, they get compressed and eventually form rock.  The presence of these visible layers is often the first indicator that a rock is sedimentary.  If you see layers in a rock it could be either sedimentary or metamorphic.  In addition to more typical rock particles like sand or mud, sedimentary rocks also often contain fragments of animal or plant materials that get compressed along with the rock particles.  Some times you can see these remains that become fossilized.  Some examples of sedimentary rocks are sandstone (layers of mostly sand), limestone (layers of mostly shells) shale (layers of mostly mud), and coal (layers of mostly plant remains).

Allowing each child to determine the order of their layers simulates the diversity of sedimentary layering in rocks.  Sedimentary rocks will have a different composition of layering depending on where they are formed (river bottom, lake), what the surrounding area is like (prairie, woodlands), and the weather conditions that occur over time (floods, droughts, ice age).  Stress to the children that the whole process takes not just a year, or even their lifetime, but often hundreds of thousands of years.

When the children tell or read their Sedimentary Sandwich Stories, they should start at the bottom and read up the page.  This is the way that geologists read rocks as well, from the bottom to the top since the bottom is the oldest part of the rock and therefore the beginning of the story.  Reinforce that the oldest parts of their sedimentary sandwiches are the layers that were put at the bottom and the newest are at the top.

By making Sedimentary Sandwiches, the children are creating a model for the formation of sedimentary rocks.  Models are important in science as a way to see something on a scale and with materials that we can understand and manipulate.  Models though are made to simulate a process in one way and may not be accurate in every detail.  In this example, children are accurately simulating the process of sediments being deposited in layers and they are learning what materials and conditions cause some of these layers.  It is unlikely that in reality all of these forms of sediment would be present in one rock, even though they might all be represented in a Sedimentary Sandwich model.  Most rocks have a concentration of mainly one kind of sediment depending on conditions and location.






WHITE SAND                White Bread

The river washes small pieces off the surrounding rocks.  These pieces of sand are carried along by the water and left on the bottom of the river.






MUD AND ROCKS           Peanut Butter

A flood washes mud and rocks into the river.






CLAY                     Brown Bread

The river is dammed so that the water barely moves.  The water no longer has the power to carry the rocks and dirt so these all fall to the bottom of the river making a layer of clay.






PLANT PARTS                     Red Jam

As the plants along the river’s edge die, their remains fall into the river and settle at the bottom.






ANIMAL BONES             Purple Jam

There are many kinds of creatures living in and around the river.  When they die, their bones fall to the bottom of the river.






DUST         Graham Cracker Crumbs

There is a drought so the area is dusty and dry. Strong winds pick up bits of dust from nearby mountainside.  These fall in the river.






ROCKS                        Raisins

A part of the riverbank falls into the river, dumping lots of rocks on the bottom of the river.


My Sedimentary Rock Story





















RIVER BOTTOM                        Plate


Metamorphic Cookies

(20 minutes)

D  Materials


2 packages sugar cookie dough (or make your own)

3 colors food coloring

stirring spoon

cookie sheet

15 pieces of waxed paper (8 inches/20 centimeters square)

oven or toaster oven


D  What to Do:

1.       Before you begin, divide the dough into 3 equal sections and add 5 drops of a different color food coloring to each section and mix in the coloring.  Divide each section into 15 balls of dough to make one ball of each color for each girl.

2.     Remind the children of safety concerns when cooking.

3.     Explain that “metamorphosis” means change.  Metamorphic rocks are formed out of other rocks and materials that become changed when they are put in extreme temperature and pressure.

4.     Give each child 3 different colored balls on a piece of waxed paper, explaining that one color represents existing igneous rock, the second color existing sedimentary rock and the third existing metamorphic rock.

5.     Have the children flatten each of their pieces as much as they can and stack them. 

6.     Next ask them to apply pressure to their “rock,” pushing down on the stack, and pushing from the sides to wrinkle the dough.  They can also fold their rock.  This represents the pressure that is involved in metamorphosis. 

7.     Have the children place their rocks on the cookie sheet and mark which one is theirs.

8.     Bake cookies as directed on package or in recipe.  Point out to the children that the baking simulates the heat inside the earth that contributes to the metamorphosis process.

9.     Once the cookies are baked and cooled, ask the children to break their cookie in half and examine it.  Discuss what they see and how the “rocks” have changed.  Ask if they see any evidence of the original rocks and how this differs from the igneous rocks.


D  Helpful Hints

1.       Check for food allergies.

2.     After coloring the dough, test if it is too sticky to handle.  If it is, add flour until dough is no longer sticky.  The children may also want to put flour on their hands.

3.     Mark which cookie belongs to whom.  You might make a grid on paper of where children placed their cookie on the cookie sheet, or have them mark their cookie by lightly cutting in their initial using a toothpick or plastic knife.

4.     If you do not have access to a cooking facility, you can do this activity with colored Play-Doh or modeling clay and just talk about the heating stage of metamorphosis.

5.     This activity is best done as the last one in the rock series so that they are already familiar with igneous and sedimentary rocks.  It does however, require cooking time, so if you are pressed for time you may need to do this one first and do Edible Igneous Rocks and Sedimentary Sandwiches while the cookies are baking.

6.     You may need extra parent help this week in order to oversee baking process.


D  Whys and Hows

Metamorphic rocks are made up of other rocks and minerals that have been heated and compressed to make a new rock.  The process of metamorphosis does not melt the rocks completely, but instead transforms the rocks into denser more compact rocks.  New minerals separate out in the metamorphosis process as the mineral components inside the rock are rearranged.  All rocks can go through a process of change, or metamorphosis…even rocks already changed in the past such as existing metamorphic rocks (one of the three colors at the beginning).  Metamorphic rocks will often still show layers, but those layers will be twisted, wrinkled and compressed due to the pressure and heat.  Some examples of metamorphic rocks are marble (metamorphosed limestone), slate (metamorphosed shale), quartzite (metamorphosed quartz) and gneiss (metamorphosed granite).


D  Other Ideas to Explore

1.       Go on a walk through the your neighborhood looking for different kinds of rocks used in the buildings, or go for a rock hunt in a rocky area.

2.     Have the children start a rock collection making cards for each new rock they add to the collection.  Encourage them to specify where they found the rocks as well as identifying them.