Rock containing halite as its main constituent. (noun)
Coarsely ground or granulated common salt. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "rock salt" in a sentence
"Madame Devalier replaced upon its bed of rock salt and cracked ice the half-shell whose contents she had been about to slurp, and, while waiting for the word 'slime" to cease its vile reverberations in her mind's ear, she poured herself another glass of champagne."
"A special type of rock salt found at Siwa valued for its chemical properties was known far and wide as the salt of Ammon—thus our term ammonia."