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Make a Slab of Metamorphic Rock

In this activity we will use a simple model and process to show how a sedimentary rock (the bread) can become a metamorphic rock by undergoing the forces of pressure and heat.
Prep Time15 minutes
Active Time1 hour

Materials

  • 2-4 pieces white bread
  • 2-4 pieces whole wheat bread
  • 1 ruler
  • 1 pencil
  • 1-2 paper plates
  • 2-3 paper towels
  • Several heavy books and some items that weigh between 8 to 10 pounds. We used a 10 pound hand weight
  • Copy of the printable - see request box below
  • 1-2 pieces Optional: You can also use other bread, like rye or pumpernickel and increase the number of total slices used.

Instructions

  • Give each person 2 to 4 slices of white bread and 2 to 4 slices of wheat bread. We mixed and matched and used anywhere from 4 to 7 pieces. You may opt to add a third type of bread. (Rye, sourdough, pumpernickel)
    rock cycle explained
  • Measure width, length, and height of each piece of bread. ("Layer of sediment") Draw a picture and record measurements in box 1 of the lab sheet.
    rock cycle explained measure the heigh of the bread slice
  • Examine each layer of sedimentary (each slice of bread.) Do you see any small pieces of sediment? Record what you see in box 1 of the lab sheet.
  • Stack the bread on a paper plate or paper towel. Line them up neatly. Lining them up uniformly helps make the effects of the heat and pressure more visible. This represents a sedimentary rock.
    rock cycle explained stack the bread to represent sedimentary rock
  • Cover the “rock sandwich” with another paper towel.
    rock cycle explained put heavy books on top to apply pressure
  • Place several heavy books on top of the covered bread. (We used two heavy textbooks.)
  • After 30 minutes remove the books and paper towel.
    rock cycle explained - measure after presure 1
  • Repeat the measurements and fill out box 2 on the observation sheet.
  • Next place the stack of bread carefully on the paper plate and cook in the microwave for 30 seconds.
    rock cycle explained put in microwave to apply heat
  • This will be hot, so use a dish towel or hot pads to remove it from the microwave. Place the dish back in your work area. Record what you see, carefully touch the top of the "rock slab." What does it feel like, record your observations in box 3 on the observation sheet.
  • Cover the bread with a paper towel. Put the books back on top of the bread.
  • Next, place the additional 10 pounds on top. We used a 10-pound hand weight.
    rock cycle explained - put extra weight on the stack
  • Wait another 15-20 minutes. Remove the heavy objects and paper towel. Measure again, record the results, and draw a picture in box 4 of the worksheet.
    rock cycle explained - measure the height of the bread stack after heat and pressure
  • Discuss what was observed. Review the questions below and on the worksheet.
    rock cycle explained the final layers of the metamorphic rock
  • Compare the before and after.
    rock cycle explained the before and after of our project