In 1890, J.J. Ott gave a remarkable concert for the Buckwampum historical society. What made the concert remarkable wasn't the music being played but the instrument Ott was playing. The instrument was made of stones that made "clear, bell-like tones" when struck by a hammer. You might say it was the first rock concert.
Ott procured the musical rocks from a nearby boulder field in Upper Black Eddy, Pennsylvania. Known today as Ringing Rocks Park, the rock field occupies 7 acres of an otherwise wooded area, and is over 10 feet deep with boulders.
Only about a third of the rocks ring, and for a long time why the rocks rang at all was unclear. However, in 1965 a group of scientists crushed, broke, and sliced the rocks. After performing numerous tests, they found that while all the rocks do in fact ring, they often do so at tones lower than the human ear can perceive. Interactions between these low tones create any audible sounds. However, the exact mechanism by which they ring still remains elusive, and it may have to do with the freeze-thaw cycle that helped created the boulder field in the first place.
Though many are tempted to illegally pocket a ringing rock for later use, it is futile, as the rocks lose their musical ability once taken away from the other stones. Other areas in Eastern Pennsylvania (the only place in the U.S. where such ringing rocks can be found) are Stony Garden in Bucks County, Ringing Rocks Park near Pottstown, Montgomery County and the Devil's Race Course in Franklin County.