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
Austin Chalk Austin Chalk The Austin Chalk is an upper Cretaceous geologic formation in the Gulf Coast region of the United States. It is named after type section outcrops near Austin, Texas. The formation is made up of chalk and marl. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus. The Austin Chalk consists of recrystallized, fossiliferous, interbedded chalks and marls. Exposures of Austin Chalk are mainly seen in quarries, roadcuts, and stream beds where the water eroded the soil. The Austin Chalk outcrops and can be seen