Rocks school series 16

 Rocks — The Three Great Families of the Earth

We learnt in school that rocks are divided into three types: igneous, sedimentary and metamorphic.

It sounded like something to memorise for an examination. But these three families tell the story of how the Earth itself is constantly changing.

1. Igneous — Born from Fire

When molten rock—magma beneath the Earth or lava at the surface—cools and solidifies, it forms igneous rock.

Granite and basalt are familiar examples.

They are, quite literally, rocks born from Earth's heat.

2. Sedimentary — Built Layer by Layer

Rocks are gradually weathered into tiny particles. These sediments are carried by wind, water or ice and deposited in layers. Over enormous periods, pressure and minerals bind them together.

Sandstone and limestone are examples.

Sedimentary rocks can sometimes preserve fossils, giving us clues about ancient life.

3. Metamorphic — Changed by Heat and Pressure

Existing rocks can be transformed deep inside the Earth by intense heat and pressure, without completely melting.

Limestone can become marble.

Shale can become slate.

The rock changes, but its material remains part of the Earth's continuing story.

And the fascinating part is that these families are not permanent categories. Through the rock cycle, one type of rock can eventually become another.

A rock may be melted, cooled, broken down, buried, compressed and transformed—over and over again.

So the rocks beneath our feet are not lifeless objects frozen in time.

They are part of a slow geological journey that has been continuing for billions of years.

We learnt three names in school.

What we were really learning was the story of a restless Earth.