Tuesday, November 29, 2011

Metamorphic Rocks

Teaching rocks and the rock cycle is rather boring.  I mean, I know I'm not a geologist, but I never enjoyed geology in school, though I was able to study and earn a high A in the class.  My kids think it's boring too, at least the vast majority of the time.  It's hard to grasp rock diversity when they're all, well, rocks.  I was wishing that the baking soda and vinegar volcano could start with "real" magma and then spew lava, rather than a runny, not-so-viscous liquid.  I stumbled across a wonderful activity for making metamorphic rocks and illustrating the change from a sedimentary to a metamorphic rock.  This was probalby the most effective lesson I've had in this unit so far.  The kids GOT IT and were enthusiastic.  Although, with my kids, I only used one hot plate so had to rotate them through in partners to do the physical part of the lab, the lab analysis, and a little bit of bookwork at their seats.  Anyway, we used sugar cubes to make metamorphic rocks.  It was surprisingly easy.  One piece of advice, though-- if using this activity for middle or high schoolers, you need to do some sort of drug comment/ snorting prevention.  Mine were threatened with a large amount of PT and a referral if I saw/ heard/ even thought something inappropriate was going on.  Unfortunately, my camera was dead for most of the day, but I was able to snap a few pictures of the kids crushing their sedimentary rocks (illustrating erosion and weathering), heating their sediment until it melted, then allowing it to harden into metamorphic rocks.

Here's what we did:

I called it something creative (not!) Sugar Cube Lab

Materials Needed: (per groups of 2)                                             

·         Safety glasses (per student)

·         Hand lens - 1

·         Sugar cube - 1

·         Aluminum foil – five inch square

·         Heat source - 1

  1. Examine the sugar cube with a hand lens and capture your observations in your notebook.
  2. What type of rock might this represent?  (Answer – Sedimentary – the crystals are still visible, was put together under pressure)
  3. Crush the sugar cube into a powder.
  4. Re-examine the sugar with a hand lens and capture your observations in your notebook.
  5. How does the sugar look now compared to before it was crushed?
  6. Now what type of rock might this represent?  (Answer – Sedimentary – no real change has occurred - the particles have just been broken into smaller pieces)
  7. Make a “boat” with your foil. Pour the crushed sugar into the foil boat. Predict in your notebook what the sugar might look like once heated.
  8. Carefully put the “boat” over the heat source. Record your observations in your notebook.  How do your observations compare to your predictions?
  9. What type of rock might this represent?  (Answer – Igneous; molten – the rock has had heat added and melted)
  10. Predict what the substance will look like when removed from the heat source; capture your thoughts in your notebook.
  11. Set the foil boat away from the heat and wait 2-3 minutes. Record your observations.  How do your observations compare to your predictions?
  12. What type of rock might this represent?  (Answer – Igneous – the melted materials were cooled and hardened)
  13. Break the hardened sugar into pieces. Record your observations in your notebook.
  14. What do the pieces remind you of? (Answer - They should resemble the original sugar cube that was crushed)
  15. How might you create a metamorphic rock using the materials you have?  (Answer:  once the melted sugar is almost cooled, add crushed sugar and mold it in a new shape with pressure – the ending product will have both materials visible.)
  16. Using your notes and observations, construct a cause-and-effect model about the forming of a each rock type based on the process(es) involved. 

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