\Tro"na\, n. [Of Egyptian or North African origin.] (Chem.
& Min.)
A native double salt, consisting of a combination of neutral
and acid sodium carbonate, {Na2CO3.2HNaCO3.2H2O}, occurring
as a white crystalline fibrous deposit from certain soda
brine springs and lakes; -- called also {urao}, and by the
ancients {nitrum}.