Science / Grades 3-5
Rock detectives
Follow the clues that show how rocks form and change.
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Three rock families
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Meet the rock detectives
A rock cannot fill out a form explaining where it came from. Very unhelpful. We can still investigate. Grains, layers, and textures give us clues. Today we will compare three rock families and follow a few paths between them.
Cooling makes a solid
When molten rock cools and becomes solid, igneous rock forms. Molten material below the surface is called magma. At the surface it is called lava. Remember the process: melted material, then cooling. Do not go near hot lava to test this.
Small pieces join up
Water and wind can move small particles. Particles may settle in layers. Over time, compaction and cementation can turn sediment into rock. Sandstone is an example. Not every sedimentary rock forms exactly this way, but this is an important path.
Change without melting
Heat and pressure can change an existing rock while it stays solid. The result is metamorphic rock. If the rock melts, that is a different step. Our rock detective must not confuse a change in solid rock with a puddle of molten material.
Pause and solve
A rock melts and later cools into a solid. Pause the video and choose its new family. Is it igneous, sedimentary, or metamorphic? The important clue is the process, not whether the rock looks pretty on a shelf.
Follow the process
It is igneous because it formed from cooling molten material. The rock cycle is not a board game with one starting square. Rocks can take different paths. Some skip steps, and some remain in one form for a very long time.
The floating rock
Here is a surprising fact. Some pumice can float on water. Gas bubbles leave spaces in this volcanic rock, lowering its overall density. It is not wearing a life jacket. Water can enter some spaces over time, so floating need not last forever.
Investigate safely
Observe a cool, safe rock with an adult. Look for grains, layers, and holes. Never taste rocks or smash them near your eyes. Write what you observe separately from what you think it means. Then continue to the worksheet for more detective work.