Blackboard ‘chalk’ are produced especially for use with blackboards in white and also in various colours. White chalk sticks are made mainly from calcium carbonate derived from mineral chalk rock or limestone, while colored or pastel chalks are made from calcium sulfate in its dihydrate form, CaSO·2HO, derived from gypsum. Chalk sticks containing calcium carbonate typically contain 40–60% of CaCO (calcite). As compared to whiteboards, blackboards still have a variety of advantages: On the other hand, chalk produces dust, the amount depending on the quality of chalk used. Some people find this uncomfortable or may be allergic to it, and according
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