IOWA 4-9 SCIENCE PROJECT
Teacher's Guide for: EDIBLE CONGLOMERATES
ROCKMIN.471 Grades 4-9
Students will investigate what a conglomerate is and how it is formed.
Students will be using observing, exploring, and inferring skills.
Conglomerates are a type of sedimentary rock made of pebbles, sand, clay, silt, and
gravel cemented together by pressure and chemicals that precipitate out of water
such as calcium carbonate and silica. The size of the rock fragments is determined
by the strength of the current which carried and deposited them.
Conglomerates contain pebbles of different types of rocks in a variety of shapes and
sizes. Popcorn balls can resemble real conglomerates by adding colored marshmallows,
candy (like M&M's) and nuts. In addition, conglomerates are formed under pressure
and cemented together by precipitated chemicals: similarly, popcorn balls are cemented
together by the students' hands and a syrup mixture.
You can use any popcorn ball recipe. The more different colors and kinds of candy
etc. you use the more realistic it will be. It is best if you have adult volunteers
do the actual cooking, but allow the students to grease their hand and form their
own popcorn balls. Students should have chosen a selection of items to add to their ball
before they get the mixture so they can mix them right in as they make their popcorn
It doesn't matter if they examine the conglomerate before or after they make the popcorn
ball. You may want some of the students examining the conglomerates while others
are making their balls.^C
Here is a good popcorn ball recipe.
6 quarts popped popcorn
2 C. white sugar
1 C. dark corn syrup
1/4 C. stick margarine
1/2 tsp. baking soda
1 tsp. vanilla
Cook the sugar, syrup, and margarine and let come to a rolling boil, stirring constantly.
Take off the fire and add the soda and vanilla. Pour over the popcorn and stir.
Grease the pan the popcorn is put in as well as spoon and your hands. This makes
24 popcorn balls.
selection of conglomerate rocks
measuring cups and spoons
hard candy like M & M" A
hot plates, camping stove, or another stove
a baking pan or tin for each group
plenty of margarine or shortening to grease the students' hands
Give the students samples of different conglomerate rocks and have them find
out as much as they can about them. What do they look like? What do they feel like?
What do you think they are made of? This can be done before or after they make
the popcorn balls.
Divide the class into groups and give each group some of the popcorn ball mixture
in their pan and the added items. They will need plenty of grease to put on their
hands. They should mix everything together in their pan and them form the mixture
into popcorn balls. Have pieces of waxed paper available for them to set them on and plastic
wrap to wrap them.
Have the students examine their popcorn balls. Ask these questions:
How are the popcorn balls like the conglomerates? What forces were used to make the
Discuss how the popcorn balls resemble the conglomerate and what forces made the popcorn
balls (pressure, and syrup mixture). Then discuss what forces could have made the
conglomerate that would be like the forces that made the popcorn ball. (see teacher
background) You may want to discuss what other forces in nature make rocks, for example
Have the students bring in other recipes that may be similar to a different kind
of rock or allow them to bring in samples if they can explain how they are like a
rock. There may be cookies or some other kind of food. If you have already discussed
metamorphic rocks you could discuss how baking cookies changes things like baking sedimentary
rocks changes them into metamorphic rocks.
You may want students to do research to find out where some conglomerate rocks
are found and how they were formed.
For more information see "Water, Stones, and Fossil Bones" by Karen K. Lind.