Minecraft wiki entry for Magma_Block, associated text: The first image of magma blocks, as tweeted by Jeb.
Magma blocks generating above a lava lake in the Nether.
Magma blocks damage entities that stand atop carpets as well. This is a zombie.
Bubble columns created by placing magma blocks under water.
A magma block is visible that naturally generated in underwater ruins to create a bubble column.