Click image to open full size
Earth Science
Three Kinds of Rocks
Igneous, Sedimentary, and Metamorphic
Related Tools
Related Worksheets
Rocks are hard natural materials found on Earth. They can be big like a cliff or small like a pebble. Scientists sort rocks into three main kinds: igneous, sedimentary, and metamorphic. Learning about rocks helps us understand the ground under our feet.
Key Facts
- There are three main kinds of rocks: igneous, sedimentary, and metamorphic.
- Igneous rock forms when melted rock cools and hardens.
- Sedimentary rock forms from layers of sand, mud, shells, or tiny rock pieces.
- Metamorphic rock forms when heat and pressure change an old rock.
- Rock layers can show what happened long ago on Earth.
- Rocks can change slowly over time in the rock cycle.
Vocabulary
- Igneous Rock
- Igneous rock is rock that forms when hot melted rock cools and becomes hard.
- Sedimentary Rock
- Sedimentary rock is rock made from layers of tiny pieces pressed together.
- Metamorphic Rock
- Metamorphic rock is rock changed by heat and pressure deep in Earth.
- Layer
- A layer is one flat part stacked on top of another part.
- Rock Cycle
- The rock cycle is the slow way rocks can change from one kind to another.
Common Mistakes to Avoid
- Thinking all rocks are the same is wrong because rocks can form in different ways and have different looks.
- Calling every shiny rock igneous is wrong because shiny minerals can be found in more than one kind of rock.
- Thinking sedimentary rocks always look smooth is wrong because many have layers, grains, or bits of shells.
- Thinking rocks change quickly like ice melting is wrong because most rock changes take a very long time.
Practice Questions
- 1 Mia has 3 igneous rocks, 4 sedimentary rocks, and 2 metamorphic rocks. How many rocks does she have in all?
- 2 A class sorts 12 rocks equally into 3 groups: igneous, sedimentary, and metamorphic. How many rocks are in each group?
- 3 A rock has clear flat layers and tiny bits of sand in it. Which kind of rock is it most likely to be, and why?