Chalk

rocks · ocean · geology · fossils

Made from plankton. Chalk formed when trillions of microscopic sea creatures called plankton died and their hard shells and skeletons sank to the bottom of ancient oceans. Over millions of years, all these tiny pieces got squashed together and turned into solid rock.

Soft and crumbly. Unlike most rocks that are really hard, chalk is porous and soft, which means it has tiny holes in it and you can scratch or break it easily. That's why it's perfect for writing on blackboards!

Famous cliffs. The white cliffs of Dover in England are made of chalk and look like giant white walls rising out of the sea. These cliffs are some of the most famous chalk deposits in the world.

Calcite mineral. Chalk is made almost entirely of a mineral called calcite, which is the same stuff found in seashells and pearls. When you see chalk dust, you're actually looking at ancient sea creature bits.

Undersea origin. Chalk only forms in deep, quiet ocean environments where plankton shells can pile up without being disturbed by waves or currents. It's a window into what ancient seas looked like.