Floating Island

Floating islands are a type of terrain added in version 1.6.
Appearance
They appear as a mass of some type of stone with a relatively level top made of one or more layers of dirt or sand. Stone types include plain stone, limestone, sandstone, and marble. Ores or two types of stone in the same island have not been reported.
Small caves in the stone are not unusual, and gems may be found inside those, regardless of whether a gem tree is present. There may also be golden chests present, just as in underground caves. It is possible for stone or soil blocks to spawn near but completely detached (even by back wall) from a floating island.
Trees and other may spawn on top of a floating island.
Where Found
Floating islands are scattered throughout the sky, generally 100 blocks or more above sea level but below space. They can occur over land or water, and can be positioned over, under, or to adjacent each other.
Worlds started before version 1.6 can have floating islands spawn in areas not yet revealed when opened in version 1.6 and later.
Flora
Fauna
Whatever animals may spawn because of the flora present.
Notes
Since the location of floating islands cannot be predicted, attempting to find them using ladders or creating ramps from blocks is inefficient. The use of a jetpack is effective, with ladders, elevators, portals, or other means of travel installed after discovery.
Floating islands are the only places gem trees can be found.
If all of a floating island's stone is marble when it spawns, there is an increased chance of a gem tree.
Gallery
-
Example distribution of floating islands
-
A trio of floating islands
-
With palm tree
-
With amethyst tree
-
With sapphire tree
-
With emerald tree
-
With ruby tree
-
With diamond tree
-
A scorpion found on a floating island at night.
-
A golden chest spawned in a floating island's cave
-
A rare instance where a mountain and a sky island are close together.