'Sulphur' in the Bible

And this is how I saw the horses and their riders in my vision: the riders had breastplates [the color] of fire and of hyacinth (sapphire blue) and of brimstone (yellow); and the heads of the horses looked like the heads of lions; and from out of their mouths came fire and smoke and brimstone (burning sulfur).

A third of mankind was killed by these three plagues—by the fire and the smoke and the brimstone that came from the mouths of the horses.