Teacher's Guide for: EDIBLE CONGLOMERATES Luann Byerly
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 ball.

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
large bowl
mixing spoons
measuring cups and spoons
recipe ingredients
colored marshmallows
hard candy like M & M" A
pot holders
wax paper
plastic wrap
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 popcorn balls?

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 heat.

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.