Chalk produce, and thus widely used in the developing world, calcium-based chalk can be made where the crumbling particles are larger and thus produce less dust, and is marketed as "dustless chalk". Colored chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often colored), used to draw on sidewalks, streets, and driveways, are primarily made of gypsum. Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines,
Sidewalk chalk Sidewalk chalk Sidewalk chalk is typically large colored (and sometimes white or cream) sticks of chalk (calcium sulfate rather than rock chalk, calcium carbonate) mostly used for drawing on pavement or concrete sidewalks. It is sometimes used by children to draw a four square court or a hopscotch board. Blackboard chalk is typically shorter. There are several different types of sidewalk chalk, typically coming in solid-colored sticks. 3-D sidewalk chalk sets, in which each stick of chalk is created with two particular colors that appear 3-dimensional when viewed through the 3-D glasses that come with the chalk, also exist. Sidewalk