Black Crystal is an object in Chrono Cross. Appearing in Fort Dragonia as part of a puzzle, the Black Crystal is guarded by the Bunyip and cannot be activated until the guardian is defeated in battle. Along with the Red Crystal, Blue Crystal, and the others, the Black Crystal must be deactivated in order to reach the area where Lynx and the Acacia Dragoons are preparing a ritual, using the Dragon Tear, so that their Demi-human leader can switch bodies with Serge.
During the prologue of Chrono Cross, when Serge, Kid, and another randomly generated party member investigates Fort Dragonia as part of a prophesy dreamt by Serge, the Black Crystal is deactivated by the party, causing an elevator in the Fort's center to take them upwards to a grim antechamber. Once there, Serge envisions himself murdering Kid before waking up to Marge's voice and finding himself in his bedroom.