|This object exists primarily or exclusively within the Sonic Underground continuity.|
Information in this article may not be canonical to the storyline of the games or any other Sonic continuity.
The Crown Jewel, as its name would imply, is a gem that was part of Queen Aleena's crown. It has a golden yellow color and an oval shape. The jewel is said to hold mystical properties, as legends say it glows brighter the closer the gem gets to Queen Aleena. 
Years later, the Crown Jewel was seemingly found by a merchant in Emporium, who offered to sell it to Robotnik. Instead, Robotnik sent Sleet and Dingo off to fetch the gem by force. The Sonic Underground, who were spying on Robotnik, headed off to Emporium to get the Crown Jewel first. Upon finding the jewel, both parties battled each other for it across Emporium, with the Sonic Underground seizing it in the end. The rock band then began to use the jewel to track down Aleena. Upon arriving to the area where Aleena seemingly was, however, the triplets found out that the Crown Jewel they had was fake, and was meant to be used as a trap for Robotnik, although it was ultimately wasted on them.