Just How Does Salt Lose Its Savour?

Matt 5:13
13 Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men.
KJV

So, how does salt lose its savour? (Or, as Mark puts it, its "saltiness?" Mark 9:50,) Over time, can salt, just lying there, become something else? No. Salt is salt, no more salty nor less salty than it ever was? So what is Jesus saying here? How can we possibly become unsalty salt?

I feel sure that Jim Fleming gave the correct answer one day when I heard him speak in Houston. And here is the same explanation taken from his study guide for that class, "The Difficult Sayings of Jesus."

Fleming says the biblical name for the Dead Sea is "salt sea." Right near the Dead sea is a mountain, called Mount Sodom, about eight miles long and maybe a third of a mile wide, that is 98% salt. From here, and from two places along the shore of the sea, salt was gathered in Jesus' day. Mount Sodom was brown, not white because the salt was mixed with dirt.

"When you go to the market to purchase salt, you buy a mixture of dirt and salt. You take it home and put it on a plate and place it on the table. What makes this a difficult saying of Jesus is that salt does not lose its flavor. In the parable it says, 'Salt has lost its flavor.' What is going on here? In Jesus' day you picked out the white pieces from the salt and dirt on the plate on the table and sprinkled it on your food. Eventually, the lump of salt and dirt will only be dirt and it will have 'lost its flavor.' The dirt that was left then was thrown into the street and trodden under foot. Once we understand the cultural context, we understand that salt does lose its 'saltiness.'"

Mystery solved.