From Lost Fables Wiki
Fire Salts are gathered from the meteors which occasionally plummet to the surface of Gaia, and always glow a dull orange and let off a pleasant heat. Though these meteors are uncommon, they're almost invariably made wholly from fire salt. Whether this is a result of its fiery death plunge to the planet's surface or a result of everything in space other than Gaia being made of fire salts is unknown. What is known is that fire salts will aggressively go up in flames when a match is struck to it, or whenever it is struck hard enough with a hard enough object.
Gathering and Usage
Fire Salts are gathered from meteor leftovers, workers having to carefully chisel away chunks of it to be sold in marketplaces the world over. Only alchemists have use for the stuff, grinding it up to use in all sorts of potions and concoctions, from fire and heat resistance potions to magical bombs. Though vastly expensive, an alchemical explosive made from a golden apple and fire salts is almost ludicrously deadly. There are also stories of metal alloys being made with fire salt, though with what specific metal has been lost to time.