Dawsonite is a mineral composed of sodium aluminium carbonate hydroxide, chemical formula NaAlCO₃(OH)₂. It crystallizes in the orthorhombic crystal system. It is not mined for ore. It was discovered in 1874 during the construction of the Redpath Museum in a feldspathic dike on the campus of McGill University on the Island of Montreal, Canada. It is named after geologist Sir John William Dawson (1820-1899).