The Rock, about the size of a football and enclosed atop a pedestal in a glass case, is touched by Clemson football players before running down a hill as they enter the stadium on game days.
The school announced Wednesday the casing was broken and a small part of the Rock was chipped off, adding the vandalism occurred sometime on June 2 or 3.
"We take vandalism, especially of such an important part of our history, very seriously. Police are investigating," said Dan Radakovich, Clemson athletic director.
The pedestal did not sustain damage, The (Columbia) State reported.