Grade 4 (age 9-10)

Types of Rocks

Rocks fall into three families based on how they form. Magma that cools and hardens becomes igneous rock, and piled, pressed grains become sedimentary rock. Rock reshaped by heat and pressure becomes metamorphic rock, each with its own grain size and pattern. Pick a rock here to compare how it formed and what makes it special.

Three Types of Rocks

🪨 Types of Rocks

①Igneous: cooled and hardened magma

②Sedimentary: piled-up sand/soil compressed

③Metamorphic: changed by heat and pressure

④The three can transform into each other

Closer Look at Rocks

🔬 Rock Features

①Igneous: granite (large grains), basalt (small grains)

②Sedimentary: layered, may contain fossils

③Metamorphic: striped, harder than the original

④Rocks form over very long times

Summary

Igneous Rock

Magma → cools and hardens = Igneous

Granite (slow), basalt (fast) — different grain sizes

Sedimentary Rock

Piled sediment + long-term pressure = Sedimentary

Sandstone, limestone, mudstone — layered, may have fossils

Metamorphic Rock

Rock + heat + high pressure = Metamorphic

Marble, gneiss — harder than the original

🎯 Key Points

①3 types: igneous, sedimentary, metamorphic

②Igneous: magma cooling (granite, basalt)

③Sedimentary: piling and pressing (sandstone, limestone)

④Metamorphic: heat+pressure changes (marble, gneiss)

⑤The three transform over long time scales

Examples and Unit Test

Example 1

Between granite, which cooled slowly underground, and basalt, which cooled quickly, which has larger grains?

Igneous rock forms as magma cools, and the more slowly it cools, the larger the grains grow.

Granite cooled slowly so its grains are large; basalt cooled quickly so its grains are small.

▸ Granite (cooled slowly, so larger grains)

Slow-cooling magma gives large grains; fast-cooling gives small grains.

Example 2

What is the rock made by sand and soil piling up and being pressed, and the rock whose nature changed under heat and pressure?

When sand and soil pile up and harden under long-lasting pressure, they become sedimentary rock.

When an existing rock changes its nature under high heat and pressure, it becomes metamorphic rock.

▸ Piled and hardened = sedimentary / changed by heat and pressure = metamorphic

Sedimentary rock forms by piling up; metamorphic rock forms by heat and pressure.

Unit-test style

Which statement about types of rock is correct?

①Igneous rock forms from piled-up sand

②Metamorphic rock is rock whose nature changed under heat and pressure

③Basalt cooled slowly so it has large grains

④Sedimentary rock forms from cooled magma

⑤The three types of rock never change into one another

▸ ② Metamorphic rock is rock whose nature changed under heat and pressure

Metamorphic rock forms when an existing rock changes its nature under high heat and pressure.

Igneous rock forms from cooled magma and sedimentary rock from piled sand (① and ④), basalt cooled quickly so its grains are small (③), and the three rocks change into one another over a long time (⑤).

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