The Matriorb is a greyish ball covered in what appears to be troll horns. Found in the abdomen of Kanaya Maryam's Lusus, a Virgin Mother Grub. It must be protected and used to hatch another Mother Grub. It's not as likely to prove a plot-centric device as it was hinted to. It's practically covered in weird plot shit. Kanaya planned to use it to save the troll race after the completion of Sgrub. She safely stored the orb in her Chastity Modus, which prevented it from being removed until the timing was exactly right.
After the trolls fled to the veil, Kanaya finds the key to unlock the Matriorb from its card. This makes her believe that she is supposed to hatch the new Mother Grub in the center of the asteroid, and not in the new universe, as she had previously assumed; instead, though, the orb is " " by Eridan Ampora, leaving the troll race seemingly doomed to extinction.
She has possibly used it in alchemizations, as she is wielding a chainsaw with troll horn teeth. It can also be used to make Jane's hat along with Charles Dutton's Dream Bubbles book and a potted plant . This also leaves open the possibility of alchemizing a new Matriorb in some manner, though Kanaya mentions that she was never able to duplicate it because The Grist Cost Was Astronomical.
Recently, the Condesce has commanded a captured Roxy to steal the nonexistence from the essence of a Matriorb with her Rogue of Void powers, causing one to exist. Roxy finally on the victory platform post-retcon, in Act 6 Act 6 Intermission 5, with the help of Calliope's presence. Roxy later brings the new Matriorb to Kanaya, a gift that she takes graciously. This is very emotional for her, seeing as she lost the first one so shockingly.