Nephrite

The Centipeetle Mother was host of the centipeetle group that raided Steven's bedroom in "Gem Glow." It also appears in "Monster Buddies", where Steven tames the Centipeetle Mother in its smaller form (which it acquired after Steven popped it's bubble) and sacrifices itself to save Steven. Steven says "I will heal you someday," but it is unknown whether the Centipeetle Mother will return again. It was confirmed that the Centipeetle is a gem in Ocean Gem.

Steven Universe Trivia

 * The Centipeetle Mother returns in the episode "Monster Buddies"
 * When the Centipeetle Mother was reforming itself after it escaped from the bubble, it took a humanoid form before taking its latest form.
 * This could be the case with all Gems.
 * It can still eat with its mouth, even though its eye is also in its mouth.
 * The gem in its mouth somewhat resembles an Emerald colored Poké-Ball from the Pokemon series.
 * Steven befriended the Centipeedle, to the extent that it sacrificed itself in order to save Steven.
 * It has a phobia of Garnet's gauntlets because Garnet threatened it with them in the temple.
 * It was revealed in the episode Ocean Gem that the Centipeedle, along with other monsters, was previously a gem. Unfortunately, the gem became corrupted, turning it into the monster it is now.
 * It is reasonable to assume the humanoid form it took on before transforming again is it's form before corruption.
 * Many fans speculated the Centipeetle Mother used to be a Gem called Malachite, but Ian Jones-Quartey confirmed that the corrupted Gem that it used to be is not Malachite.