Fiery Brimstone

Fiery Brimstone was a low-level crafting material in Diablo III, obtained by making the Blacksmith salvage legendary weapons and armor, and set items. It was also possible to find one amongst the haul of a Rift Guardian for players at levels 1-60. Each item with an item level of 1-60 salvaged would yield 1 Fiery Brimstone. They could be stacked up to a maximum of 5000. Fiery Brimstone, along with Exquisite Essence and Iridescent Tear, were the only crafting materials that are not account bound.

As of patch 2.3, they are no longer obtainable.

"Artisans through the ages have relied on rare materials to enhance and create powerful items."

Trivia

 * gloves, due to their poor performance in pre-Reaper of Souls state, were often abbreviated as FB, meaning "free brimstone", implying their only use as salvageable trash.