A traditional holiday threat by both exasperated parents and sly Secret Santas, A Lump of Coal is what you'll find in your stocking if you weren't a good little boy this year. Or girl. Or even goblin.
Typically found as a roughly fist-sized lump, A Lump of Coal is similar to the somewhat more polyhedral popular dice used in many RPGs, except that it doesn't matter which side winds up on top when you roll it. But hey, you can always use it for heating.
A Lump of Coal can be found in versions ranging from matte black to dull gray.