Why Do Some Stones Float?

Most stones sink in water. You drop a rock in a lake. It goes down. It hits the bottom. This is normal. Heavy things sink.

But some stones float. They stay on top of the water. How?

These stones are special. They are volcanic rocks. Scientists call them pumice.

Pumice comes from volcanoes. A volcano is a hot mountain. It throws out melted rock. This rock is called lava. Sometimes, the lava has many air bubbles inside. It looks like a hard sponge.

The air bubbles make the stone light. Water is heavier than the stone with air. So, the water holds the stone up. The stone floats like a boat.

Pumice is very useful. People use it to scrub skin. It is rough. It cleans dirt away.

Nature is full of surprises. Not all rocks are solid and heavy. Some rocks are full of air.

Do you have a favorite stone?