Where does beach sand come from?

How it works

Rain, frost and tree roots slowly crack rocks in the hills, and rivers carry the broken pieces down to the coast. There, waves roll the stones back and forth thousands of times a day. They knock and rub against each other, their sharp corners wear off, and they get smaller and smaller until they are sand. Waves breaking up sea cliffs make sand too.

Sand also contains bits of shell, coral and sea urchin skeletons left by sea creatures. Different beaches have different colours. Many sands are mostly quartz, a tough mineral that is pale or golden. Tropical coral beaches are often dazzling white, and sand worn from volcanic rock is black.

Look at sand under a magnifying glass and you will see that the grains come in all sizes, colours and shapes, some glassy, some speckled, some pink or white. Each grain is a tiny piece of a rock or a shell, and it carries clues about where it came from.

Where to see it in New Zealand

Piha and other beaches on Auckland's west coast have black sand. It is rich in iron that comes from volcanic rock, and it gets very hot underfoot on a sunny day. In Abel Tasman National Park the beaches are golden, made from nearby granite rock that has broken down.

Try it together

At a black-sand beach with an adult, put a magnet inside a sealed plastic bag and drag it through the sand. Does a fuzzy layer of dark iron sand cling to it? At any beach, look at sand with a magnifying glass and hunt for bits of shell.