The Fire Jet is a block from the Twilight Forest mod. This block can be found naturally in the Fire Swamp biome within the Twilight Forest dimension. They are found with a 3x3 of lava source blocks underneath, so harvesting them can be moderately tricky. These blocks will adapt the biome's foliage color to better hide itself. They will consume a single block of lava underneath it, and in trade will shoot a beam of fire into the air above it.