The Chaos Emerald of Invisibility made the holder invisible, and at first seems to be invisible itself. However, the invisibility can be negated if the holder is covered in substances such as sand or flour.
Buried on Shark Island in the time of pirates, the Chaos Emerald of Invisibility was first found by Sonic and Tails in attempts to keep it out of Robotnik's hands. Robotnik was able to obtain it from Sonic and escape in his time machine, but Sonic stole it back by disguising himself as a time cop and buried it back in its treasure chest on Shark Island.
Having the last of the four emeralds, Robotnik transformed into Supreme High Robotnik, but he was defeated by Sonic and Tails. The Chaos Emerald of Invisibility was returned to its rightful place in time, as were the other three emeralds.