This information pertains to an older version of the mod. This item was removed in Botania version R1.9 322.
The Unstable Beacons are a set of 16 decorative blocks added by Botania. When placed, they will rapidly fire beams into the sky that extend into a cloud identical to the cube's actual colour. They have no other purpose except for decoration.
Unstable Beacons can also be turned into a portable utility item, the Signal Flare.