Minecraft wiki entry for Amethyst_Cluster, associated text: They can also be placed on some other blocks for decoration, but it's only possible to place them on certain types of blocks. Most blocks have not yet been tested, but it seems that they can only be placed on full blocks, or those sides of blocks that form a full surface. They can be placed on the bottom of stairs (or top of upside down stairs), but not on their side, or top. And they can not be placed on any type of fences.[more information needed]