Types of rocks
Use vocabulary for Earth's geological processes and rock types — igneous, sedimentary, metamorphic, erosion, weathering, deposition, fossil, sediment, strata, permeable, impermeable — and apply these when explaining how rocks form and how landscapes change over time
What a learner can do afterwards
- Correctly classify igneous, sedimentary, and metamorphic rocks and explain in one sentence how each type forms
- Use 'erosion', 'weathering', and 'deposition' correctly as three distinct stages in a sequence
- Explain how fossils form using 'sediment' and 'sedimentary rock' correctly
The lesson
Every rock on Earth is one of three types: igneous, sedimentary, or metamorphic. The type tells you the story of how that rock was made. Igneous rock forms when melted rock, called magma, cools and hardens into solid stone. If the magma cools slowly underground, the rock grows big crystals. If lava cools fast on the surface, the crystals stay too small to see.
Sedimentary rock forms differently. Wind and water carry tiny bits of rock and sand, called sediment, and drop them in layers called strata. Over thousands of years, new layers press down on the old ones until the sediment squeezes into solid rock. Some sedimentary rock, like sandstone, is permeable, which means water can soak through it. Other rock is impermeable, which means water cannot pass through.
A fish dies and sinks to the bottom of a lake. Sediment slowly covers its body, and more sediment keeps piling on top for thousands of years. The sediment turns into sedimentary rock, and the shape of the fish stays pressed inside it. That is a fossil.
Metamorphic rock forms when heat and pressure inside the Earth squeeze an existing rock without melting it, changing it into a new kind of rock. Remember: weathering breaks rock apart, erosion moves the pieces away, and deposition drops them somewhere new. Three different jobs, three different words.
Igneous, sedimentary, and metamorphic rocks form in different ways, and weathering, erosion, and deposition are three separate steps, not one blurry process.
Watch it
Where it sits
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