This chest is essentially a chest made out of Nether materials, they naturally generate in Nether fortresses.
B = Nether brick (Block) N = Netherrack G = Gold Ingot
N N N
B G B
B B B
They act exactly like normal chests, the only difference is their appearance.
They look like chests, but with a Nether Brick texture, except the Netherrack top (allowing someone to light them on fire to protect from stealing), and rather than an Iron/Silver looking piece in the middle, it looks gold.