dawsonite, a carbonate mineral, NaAlCO3 (OH)2, that is probably formed by the decomposition of aluminous silicates. Of low-temperature, hydrothermal origin, it occurs in Montreal, where it was first discovered; near Monte Amiata, Tuscany, Italy; and in Algiers. In the oil shale near Green River, Wyo., U.S., it occurs as extensive beds that constitute a source of aluminum. For detailed physical properties, see carbonate mineral (table).