Canning with ice cream rock salt
"Rock salt" is not necessarily a food-grade product. That generally means it is not milled or packaged in sanitary conditions and there are no guarantees that there are not contaminants in the salt itself. It is a large grain or crystal salt and does not dissolve readily like canning/pickling salt or table salt. The large crystals also mean it would measure very differently by quantity if you measure by spoons or cups instead of weight.
We recommend against using it in food products.