Magma Block

A magma block is a light-emitting naturally-occurring block found in the Nether and the Overworld. It causes fire damage when stepped on.

Natural generation
In the Overworld, magma blocks generate at the bottom of ocean ravines and in underwater caverns.

Magma blocks also generate as a part of underwater ruins.

Mineral veins
Magma blocks can generate in the Nether in the form of mineral veins. Magma blocks attempt to generate 4 times per chunk in veins of size 33, from altitudes 0 to roughly lava sea level, in all biomes.

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

Damage
Magma blocks damage living entities standing on top of them even if underwater (with exceptions such as shulkers or guardians), 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 (which loses durability), the Resistance potion effects, and the Protection and Fire Protection enchantments. The player can avoid being damaged at all, either by, using a potion of fire resistance, or by wearing Frost Walker boots.

Magma block damage does not set mobs or players on fire, and thus does not cook the animals that it kills.

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

Magma blocks have a few specific death messages. If a player or named pet is killed simply from standing on the block, the death message displayed in chat is: "[player] discovered the floor was lava". If a player or named pet was pushed to their death onto magma blocks, the message is: "[player] walked into danger zone due to [player/mob]".

Behavior
Magma blocks emit a light level of 3.

Magma blocks emit smoke particles under rainfall, much like lava.

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).

When a magma block's top is lit on fire, the fire burns indefinitely.

Bubble columns
When a water source is directly above a magma block, a whirlpool bubble column is created, going upward to the highest water source block. Anything encountering the bubble column is pulled down, including items, boats, players, and mobs.

A player can restore breath by entering a magma block's bubble column.