When Sonic the Hedgehog was transported to the Shadow Dimension, a bespectacled shadow accidentally revealed that smashing the Black Emerald would destroy them all, so Sonic went to do just that. His progress was impeded by one shadow touching Sonic and taking on his appearance and abilities, but rather than fight, Sonic merely hurled the Black Emerald to the ground and the fake wasn't fast enough to catch it. With the Emerald gone, the Shadow Dimension began to be ripped apart. Sonic (along with Johnny Lightfoot) were teleported away just in time.
The Black Emerald resembles the Chaos Emeralds, but is not known to be connected to them.