Salt

Ought ye not to know that the Lord God of Israel gave the kingdom over Israel to David for ever, even to him and his sons by a covenant of salt?

2 Chronicles 13:5 KJV

Salt

Class: Halide. Composition: sodium Chloride. Formula: NaCI

Salt is a common mineral, with many different varieties abundant.  The most likely form of salt that the Bible was talking about is sea salt.  Salt has been used as a preserver since ancient times, with salt mines being one of the easiest ways to get at it.  However, mineral salt was not readily obtainable everywhere, so an alternative coastal source was used instead.  The usual way of harvesting sea salt was the evaporation of water from the brine of the sea.  In warm climates, this could entirely be done using solar energy, but in other climates fuel would have to be used. For this reason sea salt production is almost entirely an industry in the Mediterranean and other warm places.  Salt is also mentioned in the Bible in Genesis 14:3, 19:26, Leviticus 2:13, Numbers 18:19, Deuteronomy 29:23, Judges 9:45, 2 Samuel 8:13, 2 Kings 2:20, 21, 2 Chronicles 13:5, Ezra 6:9, 7:22, Job 6:6, Ezekiel 43:24, 47:11, Matthew 5:13, Mark 9:49, 50, Luke 14:34, and Colossians 4:6.