The rock cycle is made up of three different rock types: sedimentary, igneous and metamorphic. Throughout the rock cycle, rocks might settle together to become sedimentary rocks, melt and reform to become igneous rocks and join together under intense pressure to become metamorphic rocks, over and over again. In order to help your students understand each step of the rock cycle in a hands-on way, you can use these edible activities.
Sedimentary rocks are surprisingly easy to represent. Most solid, non-cook foods can represent sedimentary rocks, since they entail several edible materials combined together without intense pressure or incredibly high heat. (They will entail some heat or pressure, but very little relative to the other rocks types.) You can make Rice Krispy treats with your students made by mixing the cereal with marshmallow fluff and pressing it into a pan, or you can use peanut butter to stick small cereal pieces together for a similar effect. As a healthy alternative, you can make any healthy no-bake granola bar recipe, using honey to stick together oatmeal, granola, raisins and other basic ingredients.
Igneous rocks form when rocks are heated to the point where they melt and become magma, and then cool and solidify again. You can represent this process by simply melting chocolate and then allowing it to reform. Students may enjoy pouring the molten chocolate into candy moulds to show how the magma takes on the form of the location in which it solidifies. You can also make chocolate chip cookies, which begin as balls but slowly melt and reform as circles.
Metamorphic rocks form when two rocks are subjected to extreme pressure and mould together to form a new rock. To represent this process, you can take two taffies, place them in a stack on top of a piece of waxed paper, cover them with a second piece of waxed paper, and then instruct students to subject them to pressure (through squishing or pounding) in order to join them into one piece of taffy. You can also use two pieces of bread--perhaps whole grain and regular--pressed together with a rolling pin, or two colours of edible play dough.
Putting It All Together
Throughout these activities, discuss with students what they have learnt about rocks through making these edible treats. They may notice that the molten rock can be melted and reformed again and again, that the metamorphic rock has two different colours or layers in it just as some rocks do, or that you can see each of the ingredients in the sedimentary rock easily and that they haven't seemed to change their form. This can lead to a deeper understanding of the differences between these three basic rock types.
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