Long 100m abseil into American Beauty on heavy 12mm static access rope. Rigged from boulders, jumper used to protect rope at boulders and carefully laid over broken slope at the top of the climb. 3 climbers abseiled down the rope, smoothly no bouncing and no problems. After ascent and about to pack up friends came over to do the same route so we offered them our ab rope still in situ to save time. As the first climber started to descend he noticed damage to the abseil rope so aborted and swapped to another rope. The original rope had had its mantel cut through(90%) , but all cores intact. Probable cause was sharp rock hidden in the grass/ moss at the top of the abseil descent as the rope goes over the edge.