This is a custom item for my Sonic the Hedgehog Jakks figures I made. I had an extra purple Chaos Emerald. So, I decided to repaint it into the Ancient Onyx (a.k.a. the Black Chaos Emerald) from the Archie Sonics. In the original Archie Sonic timeline, since the Master Emerald wasn't created until the battle against Mammoth Mogul in issue #56, this black emerald was where Chaos along with Tikal were imprisoned in. I used Tamiya acrylic flat black paint to repaint the extra purple emerald into the Ancient Onyx.