Made from the remains of tiny sea creatures, chalk is a soft, whitish rock. It is a type of limestone. Chalk has many uses, from manufacturing to medicine.

Where chalk is found

Chalk is found throughout much of northwestern Europe. England's famous white cliffs of Dover are made of chalk. Major chalk deposits in the United States occur in Arkansas, Louisiana, Texas, and Wyoming.

How chalk is formed

Chalk is made up mostly of the shells of tiny sea creatures. When these animals die, their shells sink to the sea floor. Mud covers and mixes with the shells. After many years layers of shells and mud build up. Eventually this material hardens into chalk deposits. If the water level drops, the rock is raised above sea level. Chalk cliffs are formed in this way. The largest chalk deposits were formed during the Cretaceous period, which lasted from about 144 million to about 65 million years ago.

Physical features

Chalk is white or gray, soft, and porous, meaning that water can seep through it. Rainwater easily soaks into chalk. After many years lots of rainwater can collect in a layer of chalk. Such layers of water-soaked rock are called aquifers. (Aquifers often supply drinking water to cities and towns.) Oil and natural gas can also collect in chalk. Large reserves of oil and gas are located in chalk layers of the North Sea and the Gulf of Mexico.

Uses

Chalk is a useful material. Powdered chalk is an ingredient in toothpaste and stomach medicines. It is also used to make putty, paint, rubber, cement, and fertilizer. Factories use chalk when manufacturing iron and steel. Carpenters use string coated with powdered chalk to make straight lines on boards. Gymnasts and rock climbers rub powdered chalk on their hands to give them a better grip.

Artists have drawn with chalk for thousands of years. Teachers and students have long used chalk to write on blackboards. However, the sticks of chalk that artists and teachers use sometimes do not contain true chalk. They often are made of a mineral called gypsum and colored substances called pigments.