seegongsik
Grade 4 (age 9-10)

grade 4 Types of Rocks

The black, hole-riddled stones of island stone walls, the speckled sparkling stone of a school's front steps, and the smooth white stone of a museum statue were all made in different ways. By how they formed, rocks are split into igneous rock, cooled and hardened magma; sedimentary rock, grains that piled up and were pressed hard; and metamorphic rock, existing rock changed by great heat and pressure. So looking at a rock's grain size, whether it has layers, and whether it has stripes lets you work out how it was made. Pick each rock with the buttons to see where it sits in the cycle, then compare how it forms and what it looks like in the lower picture.

Three kinds of rock

🪨 Three kinds of rock
①Igneous rock: magma that cooled and hardened underground or on the surface
②Sedimentary rock: gravel, sand, and mud that piled up and were pressed hard over a long time
③Metamorphic rock: existing rock changed by great heat and pressure deep underground
④The three kinds of rock change into one another over a very long time as they wear away, pile up, and melt

A closer look at rocks

🔬 Telling rocks apart by their look
①Granite cooled slowly underground, so its grains are big enough to see with the naked eye
②Basalt cooled quickly on the surface, so its grains are small and it has many holes left by escaping gas
③Sedimentary rock shows layers lying side by side and sometimes contains fossils
④Metamorphic rock gets stripes or regrown grains, so it looks different from the rock it came from

Summary

Igneous rock
Magma → cools and hardens = igneous rock
Granite (cooled slowly) and basalt (cooled quickly) have different grain sizes
Sedimentary rock
Gravel · sand · mud pile up + pressed for a long time = sedimentary rock
Conglomerate, sandstone, mudstone, limestone: they have layers and sometimes fossils
Metamorphic rock
Rock + great heat + great pressure = metamorphic rock
Its look changes, as limestone becomes marble and granite becomes gneiss
🎯 Key points
①By how they formed, rocks are split into igneous, sedimentary, and metamorphic
②Igneous rock is cooled, hardened magma (granite, basalt)
③Sedimentary rock is grains piled up and pressed hard (sandstone, limestone)
④Metamorphic rock is rock changed by heat and pressure (marble, gneiss)
⑤The three kinds change into one another over a very long time

Examples and Unit Test

Example 1
Granite cooled slowly underground and basalt cooled quickly on the surface. Which has bigger grains?
1
As magma cools in igneous rock, grains grow, and the slower it cools, the more time they have to grow.
2
So granite, which cooled slowly underground, has big grains, and basalt, which cooled quickly on the surface, has small grains.
▸ Granite (it cooled slowly, so its grains are big)
The white, black, and pink grains in granite can each be seen with the naked eye.
Example 2
What is a rock made of piled-up, pressed sand and mud called, and what is a rock changed by heat and pressure called?
1
When sand and mud pile up and are pressed hard over a long time, they become sedimentary rock.
2
When existing rock is changed by great heat and pressure deep underground, it becomes metamorphic rock.
▸ Piled up and pressed = sedimentary rock / changed by heat and pressure = metamorphic rock
Limestone changed by heat and pressure becomes smooth marble, which is often used for statues.
Unit-test style
Which statement about kinds of rock is correct?
①Igneous rock forms when sand piles up
②Metamorphic rock is rock changed by heat and pressure
③Basalt cooled slowly, so its grains are big
④Sedimentary rock forms when magma cools
⑤The three kinds of rock never change into one another
▸ ② Metamorphic rock is rock changed by heat and pressure
1
Metamorphic rock forms when existing rock is changed by great heat and pressure.
2
Igneous rock forms from cooling magma and sedimentary rock from piled-up grains (①·④), basalt cooled quickly so its grains are small (③), and the three kinds change into one another over a long time (⑤).
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