a carbonate mineral, hydrated sodium carbonate (Na₂CO₃·H₂O), found near saline lakes as an evaporation product or on arid soil as an efflorescence. It is usually associated with natron (Na₂CO₃·10H₂O) and trona, which alter to it upon partial dehydration; many reported deposits of natron are probably thermonatrite, because normal temperatures and dry air will cause the alteration. Natron, commonly found in solution, was used by ancient Egyptians (Egyptian religion) as a preservative in mummification. For detailed physical properties, see carbonate mineral (table).