Magma Block

Magma Blocks are light-emitting blocks found in the Nether and in the Overworld. It causes damage to players or mobs that step on it.

World Generation
Magma blocks can be found on the shores of the Nether, or as the "shell" of underground lava lakes.

Breaking
Magma blocks can be mined with any kind of pickaxe.

Usage
Magma blocks damage most mobs, with the exceptions being Blazes and Zombie Pigmen. It could be used in mob farms to damage mobs without player interaction.