Alexandrite (アレキサンドライト, Arekisandoraito) is one of the Gems who worked at the School as an expert on The Lunarians and is among the gems that accompanied Phosphophyllite to the moon. They do not research The Lunarians because they are interested in them, instead, they conduct the research as an attempt to overcome their condition. Alexandrite conducts this research in order to retain the "fresh feeling of hatred" that they have for The Lunarians as a result of Chrysoberyl being taken from them. Kongō forbade Alexandrite from seeing the Lunarians as it causes them to go into a battle frenzy. They are one of the older gems, however, their age is unknown.