Chalk

Chalk was once thought to derive from the remains of microscopic animals or foraminifera. In 1953, however, it was seen under the electron microscope to be composed chiefly of  unicellular lime-secreting algae, and hence primarily of plant origin.

Chalk Flickr

In prehistoric times lumps of colored earth or chalk were used as markers. The lead pencil first came into use in the 16th century.

Greek and Roman women used various white powders (white lead and chalk) as make up for a fair complexion.

The Chinese used baking soda or chalk as toothpastes in medieval times.

Alfred the Great commemorated his Victory at the Battle of Edington with a chalk white horse on the downs near Westbury, which still can be seen today.

Crayola means “oily chalk.” The name combines “craie” (French for “chalk”) and “ola” (short for “oleaginous,” or “oily”).

Thomas Edison invented a receiver that contained a button-sized chalk diaphragm. This chalk receiver was widely used for many years, particularly in England.

Blackboard chalk is not real chalk. It is really plaster of Paris, but often people call it "chalk".

Tailors' chalk is not real chalk either. It is really talc. Tailors use it to draw on material when they are making clothes.

Ants will not cross a line drawn with chalk.