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Description: This chemical sedimentary rock is dominated by the mineral gypsum, a calcium sulfate mineral (CaSO₄ · 2H₂O). Chemical sedimentary rocks form when mineral sediment precipitates directly from the water column and accumulates in a basin, such as a shallow marine environment. More specifically, this rock is known as an ‘evaporite’. Evaporites form when salty sea water becomes isolated in a setting where the rate of evaporation outpaces freshwater input, causing the salt concentration of the water to steadily increase until dissolved components (like calcium and sulfate ions) reach their saturation point and precipitate minerals from the solution (e.g., think of a boiling pot of salty water on the stove. Once all the water evaporates, only the salt is left at the bottom of the pot!). During the Late Carboniferous, much of the Maritimes was covered by a shallow sea known as the Maritimes Basin. Periodically, parts of this sea must have become isolated from the open ocean allowing the water within these zones to become saltier through evaporation and formed thick accumulations of gypsum (and some other minerals like halite, sylvite, and calcite).