large pebbles -- small pebbles -- large gravel -- small gravel -- sand
We used our sifting screens last week to sort Earth materials into these 5 categories. Yesterday started to explore our smallest-known rock :: sand.
We looked at sand, we felt sand, we listened to sand. We explored the sand we were each given. Then we put it into a vial.
After that, we added water to our vial. We know that water is a great scientific tool for sorting and changing rocks. Our clean, clear water suddenly turned dark brown! We said it looked like "coffee" and "hot chocolate" and "mud". We predicted what would happen after we left our vials still for a whole day. Most of us thought it would look like it did before we added water - it was our experience that sand seems to absorb water. Some of us predicted the water would become clear again. Others of us thought the sand would dissolve into the water.
We then waited 24 hours to check on our vials. None of our predictions had been quite right! The vial still contained water and it still contained sand. But now it seemed to have another layer of something inside of it! What could it be?
Since it was on top of the sand, we guessed it was something smaller or lighter than sand. And we were right! It's silt! Silt is a rock material that is smaller than sand. We carefully poured out the water and got to touch the silt. It was smoother than the sand. It felt slimier.
Now we know lots of rock types when we sort by size:
Large Pebbles -- Small Pebbles -- Large Gravel -- Small Gravel -- Sand -- Silt
I wonder if there is any thing smaller than silt?
