trona, an evaporite mineral, hydrated sodium bicarbonate [Na3H(CO3)2ยท2H2O], occasionally encountered as a saline lake deposit or evaporation product and as an efflorescence on arid soil. Usually associated with natron, thermonatrite, halite, and gypsum, it occurs near Memphis, in the Lower Nile Valley; widely in the soda lakes of Africa, Armenia, Iran, and the western United States; and in the alkali deserts of Mongolia and Tibet. For detailed physical properties, see carbonate mineral (table).