Calcium sulfate an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice: This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an
Chalk outline fairy" is occasionally used to describe an officer that makes the chalk outline, often without authorization and while unwittingly contaminating the scene. While the use of chalk is uncommon, investigators may make smaller marks, or use removable flags, index cards, or even markers, to indicate important positions, particularly if other references are not available. Chalk outlines of bodies are familiar tropes in popular culture. Often they are used in humorous ways depicting awkward positioning or meticulous precision, or portending a character's impending death by having them prematurely fall into a drawn outline. "The Naked Gun" series made extensive use of