The black onyxes resemble rough, crystal-like stone pillars that are a couple of meters tall and glow purple and black. They are highly durable, being virtually indestructible. However, they are vulnerable to light which can make them crumble. As such, black onyxes will actively avoid light.
In gameplay, the black onyxes are completely unaffected by any of the player's normal attacks. To destroy a black onyx, the player has to stand inside a nearby light column and reflect a beam of light at it with Caliburn (the player can control the beam's direction with the Wii Remote). After being hit by the light beam for a few seconds, the black onyx will glow and then break apart.
The black onyxes can only be encountered during the Mission "Special Challenge: Rescue the townspeople" in Crystal Cave. During this mission, the player has to find and destroy five black onyxes in order to free the townspeople inside them.
- The light column can also be used to destroy enemies easily.
- The light and the Black Onyx idea, is very similar to the light that enlightens Lost World stage in Sonic Adventure