The term 'chalk', when applied to an instrument for drawing, is used loosely to describe various natural substances formed into sticks for the purpose of drawing or writing.

White chalk is limestone-based. In contrast, black chalk is made from carbonaceous shale found in northern Italy and France. A further variety, red chalk, is a rare form of clay. This last form, introduced in the late 15th century, was favoured by the artists of the High Renaissance, and later especially in the 18th century.

Leonardo da Vinci
about 1499-1500
Leonardo da Vinci: 'The Leonardo Cartoon'
Agostino Carracci
about 1599
Agostino Carracci: 'A Woman borne off by a Sea God (?)'