Luther, a former student, hunted her other students for their crytals, and killed her in pursuit of the completed stone. After Luther's death, the incomplete Stone was recovered and kept in the Director's Gallery at Watcher Headquarters under lock and key.
When Methos became desperate to save Alexa Bond's life, he too, turned to the legend of the Stone and tried to steal it from Watcher HQ in bid to save her. "Do you know anything about the Methuselah Stone, MacLeod? There have been stories about its power since before I was born! Who ever has it, lives forever....If there is one chance that I can save her, then I have to try." Eventually, Methos teamed with Amanda, and together they managed to steal the Stone (Methuselah's Gift).
The Stone was lost in a French river when Watcher, Daniel Geiger, attempted to steal it for himself, and was shot by Amanda. Geiger's body was eventually recovered from the river, with a piece of the Stone clutched in one hand.
Geiger managed to assemble the complete Stone for a few seconds prior to being killed, the Stone morphed from a jagged rocky lump to a multifaceted crystal sphere.