"Salt Cake" sounds edible but....wait:

salt cake
n.
Impure sodium sulfate used in making paper pulp, soaps and detergents, glass, ceramic glazes, and dyes.

or

Salt cake (Chem.), the white caked mass, consisting of
sodium sulphate, which is obtained as the product of the
first stage in the manufacture of soda, according to
Leblanc's process.
or

Early trade routes and many of the first roads were established for transporting salt. Many ancient civilizations levied taxes on salt. Salt was considered so precious that it was traded ounce for ounce for gold. In ancient China, coins were made of salt. In the Mediterranean regions, salt cakes were used as money.