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 Most people first encounter the word "chalk" in school where it refers to blackboard chalk, which was originally made of mineral chalk, since it readily crumbles and leaves particles that stick loosely to rough surfaces, allowing it to make writing that can be readily erased.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 to the American Academy of Allergy, Asthma and Immunology (AAAAI), there are links between chalk dust and allergy and asthma problems. The dust also precludes the use of chalk in areas shared with dust-sensitive equipment such as computers. The writing on blackboards is difficult to read in the dark. Chalk sticks shrink through use, and are notorious for breaking in half unless inserted in a writing utensil designed for chalk. The scratching of fingernails on a blackboard, as well as other pointed, especially metal objects against blackboards, produces a sound that is well known for being extremely irritating to most