By Elizabeth Watt

Grade level: Middle School (5 - 8)


In this activity the students will make a model of a sedimentary rock and an igneous rock in the form of two types of candy The students will be asked to use their skills in following directions to make the candy. The skills of observation will be used to compare the differences in the end products. This will include the sense of taste, as the candies will be eaten as part of the observation process. Writing skills will be used to describe how the making of each type of candy is similar to the making of a sedimentary and an igneous rock.

Teacher Background Information

This activity will require some cooperation with the Family and Consumer Science teacher(s) of your school. It would easier, perhaps, to make the fudge in a classroom with stoves. There are many ways to solve this problem and you could involve your students in the problem solving process

Student Background Information

Rocks are classified into three basic groups- sedimentary, igneous and metamorphic. In general sedimentary rocks are made from small pieces of things that are pushed and glued together. There is no heat involved in this process. Igneous rocks are made when molten material cools and hardens.


  1. Make a model of a sediments and igneous rock.
  2. Compare characteristics of the model sedimentary and igneous rocks.
  3. Suggest other candies or foods that would represent metamorphic rocks or other examples of sedimentary and igneous rocks.

Materials (per lab group)

No Bake Fruit Squares

  • 1 cup raisins
  • 1/2 cup dried apricots
  • 1/3 cup dried figs
  • 1 cup pitted dates
  • 1/2 cup candied orange peel
  • 1/4 cup candied cherries
  • 1 cup chopped walnuts
  • 2 - 3 tablespoons orange juice
  • Confectioners' sugar (powdered sugar)
  • Large mixing bowl
  • 8x8x2 inch pan
  • Sifter
  • Measuring cups
  • Grinder or bender
  • Margarine

Grind or blend together the fruits and nuts. Mix in enough juice to hold together. Press into greased pan. Chill overnight, Cut and sift sugar on top.

Bavarian Mint Fudge

  • 4 cups sugar
  • 1 3/4 cups evaporated milk 1/12 cup butter
  • 1 (12 oz) package chocolate mint wafers
  • 1/2 lb. marshmallows (approximately 32)
  • stove
  • candy thermometer
  • heavy, high-sided saucepan measuring cups 13x9x2-inch pan butter for greasing pans

Butter sides of heavy, high-sided saucepan, top to bottom. Then when fudge bubbles up, grains of sugar can't cling and unwanted crystals won't be able to form. Combine sugar, milk and butter in saucepan. Stir till it comes to boiling and all the sugar is dissolved. One sugar crystal can start a chain reaction. Wait to clip on candy thermometer till mixture boils. Cook to soft ball stage (243 to 236 OF) Remove from heat, Add mint wafers and marshmallows, Stir until blended. Pour immediately into buttered 13x9x2-inch pan. Score fudge while warm using tip of knife. (This means to make a shallow cut in the top of the fudge to mark where the squares will be.) Cut when candy is cool and firm.


  1. Obtain a piece of each type of candy for your group.
  2. Observe each piece of candy without touching it. Record your observations
  3. Cut each piece of candy into enough pieces that each lab member can taste each type of candy.
  4. Record observations about taste and texture of each candy.
    5. Briefly describe how each candy was made. Denitrify which candy is a model of a sedimentary rock and which type is a model of an igneous rock and tell why you think this.

Teaching notes

Each lab group will need a small, plastic knife to cut the candy. It might be necessary for you to make the candies at home and let the students view the finished product.

Activity Extension

Have each lab group or student suggest other possible foods that would be models of sedimentary, igneous or metamorphic rocks.