Every year thousands of people visit Ringing Rocks Park in upper Bucks County, Pennsylvania. And the reason for their visit is rather surprising – the chance to smack a boulder with a hammer.

You see, the boulders in this 70-acre park resonate with a metallic ring when tapped with a small hammer or handy rock.

While it might not be the most thrilling way to spend an afternoon, it is a fun diversion. Children especially enjoy wandering around the roughly three and a half acre boulder field tapping the rocks to hear them ring. Not all the rocks will ring and the different boulders will produce different sounds.

A ranger tells us that a 'rock concert' was held in 1890 with a brass band. It seems that a Dr JJ Ott found enough boulders to produce an octave scale and played a few simple songs for an audience of members of the Buckwampum Historical Society.

The park features a hiking trail which if you take the left fork from the parking lot will lead you to the southern edge of the boulder field. The right fork of the trail takes you to the boulder field and then on to a small waterfall.

To make the rocks ring, you'll need to walk out into the center for the boulder field away from the edges where there may be shade. Tap lightly with a small hammer or pocket spanner. Not all rocks ring so you might need to scout around for a bit. Don’t bother with the rocks on the trail to the waterfall – none ring.

So Why Do The Rocks Ring?

Apparently there is a very good explanation for what causes the rocks to ring, and we include it here for any geochemists who might be interested.

This part of Bucks County was an ancient lakebed and centuries of silt and mud deposits formed a rock layer of shale. Then about 190 million years ago, geologists tell us that magma from the earth’s interior was injected into these layers of shale. As time went by, the softer shale was eroded away leaving behind the igneous rock which contained high levels of pyroxene.

Pyroxene is a group of minerals known for their dark colour and hardness. When pyroxene comes in contact with water, a chemical reaction takes place forming a clay called montmorillonite. In the ringing rocks, a shell of montmorillonite surrounds the pyroxene and creates the sounds we hear.

Rocks in the shade near the edges have had water infiltrate deeper into the boulder and convert more of the pyroxene which is why these boulders do not ring.

The park is open daily from dawn to dusk and there are restrooms and picnic tables available.