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,
Blackboard Chalk on a black-Board”. The first attested use of chalk on blackboard in the United States dates to September 21, 1801, in a lecture course in mathematics given by George Baron. James Pillans has been credited with the invention of coloured chalk (1814): he had a recipe with ground chalk, dyes and porridge. The use of blackboard did change methods of education and testing, as found in the Conic Sections Rebellion of 1830 in Yale. Blackboard A blackboard (also known as a chalkboard) is a reusable writing surface on which text or drawings are made with sticks of calcium sulfate