Chalk It is formed in the sea by sub-microscopic plankton, which fall to the sea floor and are then consolidated and compressed during diagenesis into chalk rock. Most people first encounter the word "chalk" in school where it refers to blackboard chalk, which was originally made of mineral chalk, since it readily crumbles and leaves particles that stick loosely to rough surfaces, allowing it to make writing that can be readily erased. Blackboard chalk manufacture now may utilize mineral chalk, other mineral sources of calcium carbonate, or the mineral gypsum (calcium sulfate). While gypsum-based blackboard chalk is the lowest cost to
Blackboard Jungle film was selected for preservation in the United States National Film Registry by the Library of Congress. The film was released on DVD in North America on May 10, 2005 by Warner Home Video. Notes Sources 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