Why are there different colors of chalk?

Chalk is a sedimentary rock composed mainly of calcium carbonates, however other minerals can also be found in it. Different kinds of minerals and impurities cause different colours.

When chalk is mined, it often contains a variety of minerals and impurities, such as iron oxide, manganese oxide, and clay minerals. These minerals and impurities can give chalk a variety of colors, including white, yellow, red, brown, and black.

For commercial use, chalk can be treated with dyes or pigments to produce different colors. This can be done to make chalk more appealing to consumers or to create chalk that is better suited for specific purposes, such as writing on different surfaces or creating artwork.