Power-marbles are a special type of firemarble that explodes when struck, releasing all of their energy at once, rather than glowing softly like normal firemarbles do. They were invented by the D'ni as a way to power heavy machinery but were also developed by Gehn from regular firemarbles in his efforts to power his defective Linking Books on Riven.

It should be noted that while the firemarble thrown by Saavedro at the beginning of Myst III: Exile exploded upon impact with the wall of Atrus' study, it was not a power-marble, but rather a regular firemarble. It has been speculated that the firemarble shattered upon impacting the wall, causing it to release a large amount of energy in the process, but this energy release was still negligible compared to the apparent power output of power-marbles.