Demonite Bricks are crafted from Demonite Ore and Ebonstone. A box of it also appears after the Wall of Flesh has been defeated on a Corruption world ( in any type of world). It is not resistant to explosions, and gives off a faint glow.
Demonite Brick is the only (craftable) brick, apart from its crimson counterpart Crimtane Brick, that does not require 2 materials to make, instead requiring 6. Additionally, it is one of the only bricks that when crafted, gives you more than one block, giving the player 5 Demonite Bricks. The only other bricks are the Meteorite Brick, the Luminite Brick, and the Chlorophyte Brick.