CHALK. The Remains of Tiny Shells.

 

CHALK. The Remains of Tiny Shells.

       

    Chalk may be a soft, white, porous, sedimentary carbonate rock, a form of sedimentary rock composed of the mineral calcite. Chalk consists of the shells of such minute marine organisms as order foraminifera, coccoliths, and rhabdoliths. The purest varieties contain up to ninety nine percent calcium carbonate in the sort of the mineral calcite.

The material we call 'chalk' was formed during the time when dinosaurs lived on Earth. At that point the oceans were rising higher and bitter till finally they lined most of the land.

Billions of tiny animals lived in those oceans. They were so small you could not have seen them - they were even smaller than the full stop at the end of this sentence. These tiny creatures had shells made from the element calcium. When they died, their shells fell to rock bottom of the ocean. After thousands of years, there have been several layers of shells on the ocean bottom.

As more and more of the little shells ironed down from the highest, those on the bottom became tougher and start to stay together.

Eventually the shells changed into a mineral called 'calcite', the main ingredient of the rock known as 'limestone'.

CHALK. The Remains of Tiny Shells.

Many several of years passed after the primary chalk was formed. The Earth's surface changed its shape, and the land and sea developed new coastlines. This left several chalk layers on land, both in the middle of continents and by the ocean. In the south of England there are chalk cliffs 244 meters high. These are the known White Cliffs of Dover, and they are virtually solid chalk!

If you had a bit of chalk from those cliffs, you may use it to put in writing on a chalkboard. But the chalk that is used in classrooms is not dug from the cliffs or the ground. It is made in factories by mixing several different materials together.