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 Jungle Blackboard Jungle Blackboard Jungle is a 1955 social commentary film about teachers in an interracial inner-city school, based on the novel "The Blackboard Jungle" by Evan Hunter and adapted for the screen and directed by Richard Brooks. It is remembered for its innovative use of rock and roll in its soundtrack and for the unusual breakout role of a black cast member, future Oscar winner and star Sidney Poitier as a rebellious, yet musically talented student. In 2016, the film was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically,