You can pinch the bits of crayon together to form a crumbly sedimentary rock.
You can hammer the bits together (in foil) to form a stronger metamorphic rock.
And you can melt them (in foil, over a candle) to form an igneous rock.
We spent some time looking at these kinds of rock from our rock collection. Pretty fascinating, especially the crystals!
We did a several crystal growing experiments.
We did slow growing rock candy (sugar crystals) which I had shown them but not explained last week.
Super fast, heat generating sodium acetate crystals in reusable hand warmers.
Seeing the three kinds showed how the speed of formation affects crystal size: slow crystals grow very large, fast crystals are tiny!
Then we looked at fossils.
At this point, we own a lot of fossils that we have found, been given, or bought!
To show the fossilization process, I had cut two "bones" out of spponges. One I let dry, the other I soaked in brine, then let dry. The dry sponge was still flexible, but the brined sponge was hard and filled with salt crystals, much like the soil minerals fill the microscopic spaces in bones and shells.
I pointed out the difference between direct fossils (like the whale vertebrae, petrified wood,and shark teeth), and impressions and casts, (like the shells and crinoids you can see in the light rock on the right and the dark rock on the left).
I allowed the kids to make casts of their favorite fossil by making an impression with sculpey (polymer clay) and then filling the impression with plaster.
It was a nice "last class" thing to let them take home their favorite fossil!
I collect bones from chickens, ribs, hams, and roasts. I actuallyput them through the dishwasher to clean them up, then let them air dry. I suppose you could also bleach them (something I do when I add wild found bones to our museum).
I mix up a big batch of plaster of paris, and hide the bones in bundles of plaster - about three bones per bundle. I try to give each one a variety of bones, but the kids will love it even if all you have are drumstick bones!
After a few days, the plaster is dry and hard, and I let the kids chip out the bones with hammers.
Older kids like to use hammers with screwdrivers and paintbrushes to get the whole paleontologist experience!