Copper blocks will cause damage if there is lava or magma beneath.

The lava or magma block would have to be one block directly beneath the copper to make this work.

This would work on Copper Slabs, Copper Stairs, Cut Copper, and Waxed Copper too.

For normal Copper, damage would be 4 hearts/half-second of fire damage.

Exposed Copper would deal 3 hearts/half-second of fire damage.

Weathered Copper would deal 2 hearts/half-second of fire damage.

Oxidized Copper would deal 1 heart/half-second of fire damage.

With burning copper you could make rooms with secret passageways and passageways as death traps.

With Pistons pushing lava out of the way you could "turn off" the fire damage of a copper passage or room.