Activity 7: Chocolate Rock Cycle
Email gg-info@lists.utah.edu for the full teacher's guide, student worksheet, and worksheet solutions.
This lab activity simulates the rock cycle with a piece of chocolate instead of actual rock. Students melt, crystallize, erode, lithify and metamorphose a single small block of chocolate. Along the way students complete questions and compare the products of each step with actual rocks.
This lab is intended for high school or undergraduate introductory Physical Geology lab students with little previous exposure to geology. Ideally students will have some previous exposure to the rock cycle, but this lab also serves as a comprehensive introduction and students require little to no background.
The lab is intended to be completed in a single 2-hour lab session (possibly a little longer for the final write up).
The content goals for this activity are based on a first-hand manipulation of the rock cycle.
- melting temperatures composition
- melting and magma mixing
- plutonic volcanic textures
- erosion
- lithification
- metamorphism
- distinguishing between igneous, metamorphic and sedimentary rocks
Students will also gain experience in the following:
- Formulation and testing of hypotheses
- Synthesis of ideas and concepts
- Working in groups
- Setting up experiments
- Evaluating experimental limitations
ROCK CYCLE IN CHOCOLATE LAB
- Materials (for each group):
- Chocolate (dark and white)
- Aluminum foil
- Wax paper
- Hot plate
- Knife (doesn’t need to be sharp)
- Piece of plutonic rock countertop (granite, gabbro, diorite, etc)
- Glass beaker with cold water (ideally sitting in an ice bath)
- Hand lens
- Small glass jar with lid
- Two Plexiglas sheets
- Clamp (for metamorphism)
Divide into groups of 2-5 (depending on how many set-ups for which you have materials). Each group will need materials to work through the following stations:
- melting
- crystallizing
- erosion / weathering / sediment production / lithification
- metamorphism
- Short-circuiting the cycle
- Comprehension
ROCK SAMPLE LIST:
A – Banded pumice or xenolithic rock
B – Aphyric basalt and/or vesicular basalt
C – Coarse-grained granite with obvious quartz crystals and other minerals
D – Medium-grained quartz sandstone
E – Quartzite
F – Folded gneiss or folded metamorphic rock (the fold is important)
G – Conglomerate with many lithologies (ideally all three major rock t