A large blue sapphire. It could be a decoration.
This jewel is acquired in a tiger-bust along with a red one just like it. To do so, the player can simply accept it when prompted; however, the power to the entire facility must be taken offline in order to have it permanently in possession. It's essential for opening the music box in a replica of Alfred's bedroom, similar to the one requiring the ant of the same color at his private house.