Magma Block

Magma blocks are light-emitting naturally-occurring blocks found in the Nether that cause fire damage when stepped on.

Obtaining
Magma blocks can be mined using any pickaxe. If mined without a pickaxe, it will drop nothing.

Natural generation
Magma blocks are found naturally in the Nether, around the level of the lava sea, between Y=23 and Y=37. They generate in large veins of similar size to dirt and a similar frequency to blocks like andesite in the Overworld, generating 4 veins per chunk.

Damage
Magma blocks damage living entities standing on top of them (with exceptions such as shulkers), dealing of damage every tick (although damage immunity reduces this to once every half-second). Magma blocks do not destroy items. Damage taken is considered fire damage and is reduced by armor, shields, the Resistance and Fire Resistance potion effects, and the Protection and Fire Protection enchantments. Armor will take damage, but a shield will not. The player can avoid being damaged at all, either by crouching, using a potion of fire resistance, or by wearing Frost Walker boots.

Blocks the height of a trapdoor or lower (such as snow layers, carpet, repeaters or comparators) will not prevent a magma block from damaging mobs and players above it.

On killing a player, the death message displayed in chat is: " discovered floor was lava". If a player was pushed to their death onto magma blocks, the message is: " walked on danger zone due to ". These seem to be references to the Archer series.

Behavior
Magma blocks emit a light level of 3. Due to a bug, it can "preserve" higher light levels in some circumstances even after the original light source is removed.

When randomly ticked and water is on top of the block, the water will be removed with smoke particles.

Magma blocks emit smoke particles under rainfall.

Mobs avoid magma blocks that are in the way. Most mobs don't spawn on magma blocks (exceptions are magma cubes, zombie pigmen, ghasts, and squids).