If you strike a rock, you’d expect to hear a dull ‘thud’. Or maybe a ‘chink’. Definitely not a ringing sound. So you’d be surprised to know that ringing rocks actually do exist. Nestled in the midst of the 128-acre Ringing Rocks County Park in Pennsylvania, is a field of unique boulders. Spread out across seven to eight acres, the boulders produce a distinctive metallic ‘clang’ when struck with a hammer or another piece of rock. Native Americans have known about the rocks for centuries, and passed on their knowledge to the first White settlers in the mid-1700s.
The sound produced by the rocks is so unexpected that it could get you wondering if they are really made of stone. They actually sound hollow and metallic. The strange phenomenon has baffled scientists and geologists for years. Several experiments have been conducted on the ringing rocks, but the exact reason for the unusual sound remains unknown.
Richard Faas, a geologist from Pennsylvania, tested a few of the rocks in his lab in 1965. He discovered that when struck, each individual rock produced low frequency tones that aren’t audible to the human ear. The tones from multiple rocks interact with each other and it’s the collective sound that we get to hear.