Minecraft wiki entry for Gravel, associated text: A naturally generated gravel patch as seen in a cave.
A naturally generated gravel floor as seen in an ocean.
A gravel patch as seen in the Nether.
Gravel shown to be not affected by gravity if there is a non-solid block (except fire) underneath it.
Gravel floating in midair next to the windswept gravelly hills.
Naturally generated gravel in a cave.
Gravel hanging above the lava sea, without any support below. Viewed in Spectator mode.