We expect a certain dull, earthy, *chink* sound when rocks are hit with a hammer. We do not expect rocks to ring like metal bells, chimes or gongs when struck. Yet, some do. The story of ringing rocks spans history, locations, and legendary themes around the world. They are seen as magical, mysterious, and scientifically curious. 

Ringing Rocks road sign
Bridgeton Township, Bucks County, Pennsylvania. Photo: Sharon Hill

It was a pleasantly warm day in mid-July when I parked in the parking lot of Ringing Rocks county park near Upper Black Eddy, Pennsylvania, and chose the less obvious left-hand trail through the trees. Within a short distance, the trees dwindled, the rock rubble increased and the shade gave way to sun and a small sea of boulders. People scrambled and jumped on the treacherous uneven surface, going at the stones with metal hammers. Some produced a clear bell-like tone. Others, a dull clank. When a particularly sonorous stone was encountered, the founder was amazed and yelled to their companions to listen. Clearly, this place and its hidden tones were surprising and amusing to the visitors young and old. 

Video: Sharon Hill

This park, also named in sources as Bridgeton (for the Township), is probably the most famous location of ringing rocks in the U.S. It has been repeatedly written about in travel logs and by chroniclers of anomalous natural phenomena. There are several sites around the world known for their ringing rocks. They are of various geological origin and some specimens have been fashioned by humans more so than others. Because of these differences, there are several possible explanations for why they ring and why similar or adjacent specimens do not. There has been less methodical investigation into this special property of stones than one would expect, considering that humans have known about and used rocks as musical and ritual instruments since before written history. 

History

Lithophones and rock gongs have been used as part of rituals since ancient times. Rocks, boulders, and cave stalactites and stalagmites show evidence of percussive use by ancient humans. Archaeologists, especially those interested in the development of music, have documented this.

Discovery and study of sonorous stones in Sudan.

The wider sub-field of archaeoacoustics examines how sound produced by the natural environment was viewed in the context of belief. Areas where rocks have sonorous properties may have been interpreted as special places of spiritual significance. Researchers speculate that shamans may have attempted to communicate with the spirits at these places. One group even suggested that the standing stones of Stonehenge ring when struck and that this was the reason the particular type of stone was used. Today, it’s difficult to test for ringing properties at historical or environmentally sensitive sites as preservationists rightly prohibit hammering on all protected features. 

The Skiddaw Stones is a lithophone dating from 1840 composed of 61 shaped and tuned rocks from Cumbria, England. Its component composition is hornfels, a dense, metamorphic rock type. Slate, also a metamorphic rock, is also used for constructing lithophones or rock chimes.

While ringing rocks can be either natural or enhanced by humans to make sound, there are numerous areas around the world where such rocks have been documented. One type of rock is known to characteristically produce a distinctive clinking sound. Phonolite is a somewhat uncommon volcanic rock of intermediate chemical composition that was named after the metallic sound it produces. Several locations that have documented ringing rocks are phonolite. Several other locations of phonolite worldwide may have the ringing feature but they have not been as widely publicized. 

Flint stones are also well documented to clink or make a unique sound when struck together. Long and slender flints are said to ring best.

Chinese style gong chimes, Musical Instrument Museum, Phoenix, Arizona
ksblack99, https://www.flickr.com/photos/ksblack99/sets/72157688950209202

Locations

Wikipedia and Corliss (1989) list various locations that have rock chimes or gongs such as Ethiopia (flint), Nigeria (granite), and China (oolitic limestone). In India, there are musical boulders of Hiregudda Hill (dolerite). African east coast coral rock is also said to be sonorous. A field of boulders in the Namibian desert are called the “singing stones”

In Australia, two locations are notable: Ringing Rocks of Kiandra, NSW – an outcrop of boulders in the Snowy Mountains, and the Bell Rock Range of Western Australia – an ultramafic intrusion near Warburton.

In France, musical flints and strips of stone from chalk beds across the country were used to make lithophones. Like Stonehenge, one source (via Corliss), says that the standing stones at Carnac also ring. Corliss also had excerpts from 1889 sources about the sounding stones of Guildo, France. Now known as the Singing Stones of Brittany, the black crystalline amphibole rock show well-worn spots where people repeatedly tested for sound. The Wikipedia entry says there is a legend that the rocks were “spewed up by the giant Gargantua” but no citation is given. This entry is also incorrect (as of this writing) in that it calls the rocks “basalt”. Only a few of the rocks produced sound, those with more iron did not ring. This suggests that the source of the ringing was a combination of composition and weathering as will come up later in this post.

Several sites in the UK are notable: limestone from Kendal and Portland, Wolf Rock – a true phonolite (Na and K-rich volcanic rock) – near Lands End, Cornwall, the Ringing Stone of Tiree, Scotland – a glacial erratic granodiorite that was clearly used for its sound characteristic, and the Ringing Stone of Ballater/Richachary in the Cairngorms National Park of Scotland. In Wales, the Preseli range dolerite is said to ring. Also of note is the village of Maenclochog which some translate as “noisy stone”. The name may be based on a legend where the local rocks rang. It’s not clear if any still do.

Two locations in Mexico – appropriately called The Hill of the Bells (Cerro de las Campanas) in Querétaro, and The Hill of the Bell (Cerro de la Campana) in Hermosillo, Sonora –  are both phonolite. 

In the US, the rocks at Devils Tower are said to ring. Again, rock hammers and collecting are prohibited in National parks and protected areas. A ringing rock “place of interest” in Butte, Montana hosts surface rocks derived from a pluton consisting of olivine basalt and granitic magma. The periglacial freezing of the bedrock during the Pleistocene resulted in a rocky peak of chiming boulders. This location is on federal land between Butte and Whitehall. Similar to the Pennsylvania boulder fields, the slightly rounded rocks have a rusty brown coating over the dense rock. According to Butler, the outcrop does not ring like the isolated boulders do. 

Ringing rocks field in Montana
Ringing Rocks, Butte, MT

Pennsylvania and New Jersey sites

By far, the most extensive, documented, and publicized areas of ringing rocks are in eastern Pennsylvania into New Jersey. There is a good reason for this. Most of these areas are geologically related and their history and setting give us a good indication of why they ring while adjacent formations do not. Pontolillo and Pontolillo documented at least sixteen locations in PA/NJ. Many were diabase features but some were slate or other metamorphic rock types. Several of these locations have been quarried, developed, or have grown over – their special characteristics lost forever. Some had more “ringers” than others. The Ringing Hill Fire Company park in Lower Pottsgrove Township, near Pottstown, PA, has a boulder field known since 1742 that was once part of an amusement park with an electric trolley for visitors. Stony Garden in Nockamixon Township, Bucks County PA is another large area in PA. These two public areas are not as popular as Ringing Rocks Park in Bridgeton Township, Upper Black Eddy, Bucks County, PA. Sometimes, writers will mix up the locations and their history due to similar names and proximity. 

Map of diabase ringing rock boulder fields
Locations of ringing rocks PA/NJ. Credit: Andrews66 – CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17626641

The areas of ringing rocks in PA and NJ are found as boulder fields or “felsenmeer” (German for “sea of rock”). These blockfields look distinct and have spawned folklore regarding their origin. But, geologically, the rock fields are formed in situ as a result of proximity to freeze-thaw weathering associated with past glacial advances. These boulder fields are all relatively young, formed within the past tens of thousands of years. 

There was no sudden catastrophe that created the felsenmeer – they were a result of steady forces breaking down the rock. The boulder fields in the Newark Basin of PA and NJ are formed from intrusive sills, layers of magma that were injected into the host rock during the early Jurassic as tectonic plates pulled apart in what was to be a failed arm of the Atlantic. During glacial times, these rock layers were exposed at the surface where they became broken, pitted and grooved.

The rock layer was devoid of soil and open to the elements. Water seeped into cracks, then froze, breaking up the bedrock into fragments. Wherry (1912) noted that these boulder fields were always found at the base of a sheet of igneous rock, over top of a layer of sedimentary rock baked by the original intrusion of hot rock thus made more resistant to erosion. The slight dip of the field, about 8 degrees, means that any sediment that formed washes away, leaving a barren field of rubble additionally jumbled by seasonal ice and runoff. 

Falls at Ringing Rocks park
Flat hornfels layer forms a waterfall at Ringing Rocks County Park, Upper Black Eddy, PA. Rounded diabase boulders sit on top. Photo: Sharon Hill

As an example, let’s focus on the major location in Upper Black Eddy where the Coffman Hill diabase blankets the layer of resistant hornfels forming a bluff above the Delaware River. With a slight dip and a solid foundation, no soil could form in this field so the rocks remain barren of most plant life. The rocks are exposed to direct sun, all forms of precipitation, and freezing open air. The margin of the field is shaded by the edging trees where the rocks have eroded and organic matter forms a blanket of thin soil. The vegetation, in turn, leads to conditions that break down the rock further. The vines, ferns, and weeds slowly encroach into the felsenmeer where boulders along the edge are partially buried in soil, hosting lichen and moss. These rocks do not ring. Perhaps, long ago, they once did. The bare rock will eventually succumb to the greenery. 

Cross section of boulder field
Generalized depiction of ringing rocks boulder field formation. Wikimedia Commons. Andrews66, CC BY-SA 3.0

Folklore

Ringing rocks certainly had a role in ritual and popular beliefs of ancient peoples. A more modern belief was that the ringing meant the rock was hollow and that gold or silver was hidden inside. This myth is invoked at the Welsh village of Maenchochog where the ringing boulders were supposedly smashed to bits to find the treasure inside.  The “Gyllenstaninen” or golden ringing stone of Fole, Gotland, Sweden was split in half in the 19th century by those who thought that the presence of gold caused the ringing. They didn’t find a treasure inside.

The starkness of these seas of rock has inspired fear and legend. When people cannot readily work out the source of the rock, they infer supernatural agency. The devil usually has left his historical mark on these legends. Ringing rocks were historically noted at places like the Devil’s potato patch near Sumneytown in Montgomery County, PA, and the Devil’s Half-Acre, now overgrown, in the Sourland Mountain preserve in New Jersey. 

An old story goes that the devil himself walked over the Delaware river in Bridgeton Township, PA where he experienced some personal calamity, sat down, and blighted the land that became the Ringing Rocks Park in Upper Black Eddy. 

Infamous Fortean writer Ivan T. Sanderson wrote about the Upper Black Eddy park in his book Things in 1967. He dramatically stated that “something was frightfully wrong here”.  He found the place to be mysterious, ignoring and rejecting what was already geologically known about the formation of the site. Instead, he exaggerated the weirdness, suggesting that the field was formed by a cosmic impact. Sanderson, a zoologist prone to paranormal speculation,  irresponsibly and arbitrarily stated he didn’t trust the whole notion of igneous intrusions. He also erroneously said that there were no plants, birds, or other life on the boulder field, and that compasses went haywire over the location. Sanderson’s fantastic misrepresentations and baseless speculation were popular and subsequently were quoted in many paranormal-themed books and, later, on websites, that perpetuated the misinformation. The Travel Channel listed the Ringing Rocks Park on a 2016 list of “supernatural places” with no basis whatsoever. Such sources promote the mistaken idea that scientists are still “baffled” about the explanation and rarely clarify that far more is known now about why the rocks ring if one only does their homework.

Fern grows in field of ringing rocks
Life finds a way. Ringing Rocks Park. Photo: Sharon Hill

The locals sometimes promote strange ideas for tourism. On the other hand, they may play it down as paranormal sensationalism can result in unwanted attention and vandalism. There are still visitors who say they feel special “energies” (positive or negative) from the areas.

Frequently, it is said that removing the rocks from their location will cause the ringing to cease. This contentious allegation is likely both true and false, depending on how long you wait and how you treat your purloined piece, as I’ll discuss in the next section. It’s possible that this outcome was popularized by locals who didn’t want all the “ringers” to be taken from their site. The trouble is mostly in hauling the very dense, heavy boulders away from their homes. 

Even more so than how the fields formed, the biggest question about the rocks from observers is “why do they ring?”

Cause of ringing

Corliss, in his catalog of anomalies citing scientific journals such as Nature and Scientific American as sources, explained that the anomalousness of ringing rocks worldwide was inherent in the observation that this rock rang but the one next to it did not. Why did these rocks ring and not others of similar type? Only a fraction of the rocks in an area will ring. Why do fragments of a parent rock ring at the same frequency? It was unexpected that randomly-shaped, unassuming rocks would produce such clear metallic tones. 

Early local settles were aware of the ringing rocks but they were almost certainly known through Native stories that suggested the areas were spiritually special. White settlers would have translated that as “cursed”. Documentation of ringing rocks is in obscure, old sources. But since their discovery, they have garnered the interest of a few scientists who tried to unlock the secret of the sounds. This has been a controversial venture. Initial causes of the ringing included ideas about metal content (gold, silver, iron) or hollowness. It was also thought that only rocks that were arranged above the ground (to vibrate freely) would ring. Researchers broke them into smaller pieces – at a certain size, they indeed stopped ringing.

With some background in geology, one can suppose that the density of the rock plays a role. Even though the local diabase is often referred to as “ironstone”, the rock does not have appreciable iron but the rusty coating was indeed an important feature. 

Video: Sharon Hill

Several scientists suspected that the crystal structure of the rock and internal stresses allowed the sound waves to be produced. Some thought that the rocks always made a “sound” because they were under stress but it could only be audible to humans if you hit it. In summary, several of the early geological speculators were on the right track but muddled the explanation and weren’t yet able to use the right technology to figure it out.

Careful testing of the rocks had only rarely been done. The most significant test was done by Gibbons and Schlossman and reported in the journal Natural History. They studied the crystal formation in microscopic cross-sections of rocks that rang and ones that didn’t. They discovered that the Upper Black Eddy site exhibited microclimatic differences between open sun and shade that caused differential weathering in the rock field. Those rocks in the open field were exposed to various factors that caused the pyroxene minerals on the surface of the rock to weather into the clay mineral montmorillonite. This change resulted in an expansion of the thin crust of the rock at the molecular level, creating new internal stresses. It was these stresses that facilitated conditions that caused audible ringing when struck. In contrast, the rocks in shade released their stresses by exfoliating their outer layers and breaking up like normal rocks. They did not develop the internal stresses necessary to produce ringing. Some paranormalists disliked this explanation. They argued that it didn’t apply to ringing rocks around the world and objected that ringing rocks removed from their place would stop ringing. Geologists Pontolillo and Pontolillo, however, confirmed this work to their satisfaction and agreed that the microclimate scenario was indeed a factor to explain why some of the boulders in the open range rang while none of the shaded ones did. 

Shaded part of ringing rocks field
Shaded field of rocks that do not ring. Photo: Sharon Hill

It’s a fair bet that there used to be many more ringing rocks than there are now. Over time, conditions change and the internal stresses are eventually released. The sound frequency of the rock may change over time as stresses build and then subside. Sanderson, who argued that the ringing rocks he brought home were still ringing, failed to understand many things, especially the pace of geologic time. 

Ringing rocks field
Ringing Rocks Park, Upper Black Eddy. Vegetation encroaches on the felsenmeer. Photo: Sharon Hill

So, the mystery of why rocks ring is illuminated but not completely understood. It seems likely that rocks exposed to cycles of sun, cold, and precipitation are prone to develop these weathering-related stresses that enhance ringing. This scenario can be applied to several sites around the world, perhaps even Stonehenge or other standing stones exposed for millennia. But other factors are certainly involved for ringing rocks of other compositions. 

There is no one answer to why rocks ring. Nature is complex and the context of each location is important. It’s also important to recognize this complexity when exposed to the popular literature of anomalistic, Fortean, and paranormal sources that emphasize the spookiness about a place or phenomenon. Even archaeological articles focused on the social use of ringing rocks promoted geologic ignorance of their origin and explanation. In many cases, these writers have never asked a geologist, or if they did, they asked one who was clueless about this niche subject. I found much misinformation propagated about this topic. It’s not the easiest or most captivating thing to explain and it takes a good deal of effort to find reliable information and sort it all out. Even now, there remains much work to be done to unlock the music of the rocks, but it’s not that mysterious. 

So, now that you know what conditions are conducive to ringing rocks, feel free to tap the occasional sunny boulder. I recall one time, years ago, I was collecting rocks in a Pennsylvania quarry with no previous indications of sonorous stones when a random sample surprised me with a pleasant tone. It was pretty magical. Even when you know that it’s natural, it’s still a fantastic moment.

References

Aldred, J., et al. (2016). The influence of solar-induced thermal stresses on the mechanical weathering of rocks in humid mid-latitudes. Earth Surf. Process. Landforms. 41: 603–614.

Barlyn, P. (2017). Seven Wonders: Ringing Rocks Park, a geological mystery in Upper Bucks. Bucks County Courier Times. Aug 1, 2017.

Butler, B. A., (1983). Petrology and geochemistry of the Ringing Rocks pluton Jefferson County Montana. Graduate Student Theses, Dissertations, & Professional Papers. 7723. https://scholarworks.umt.edu/etd/7723

Cianchetta, M. (2010). If Rocks Could Sing: The Ringing Rocks of Bucks Co. Pennsylvania Center for the Book. https://pabook.libraries.psu.edu/literary-cultural-heritage-map-pa/feature-articles/if-rocks-could-sing-ringing-rocks-bucks-co

Corliss, W.R., (1989). Anomalies in Geology: Physical, chemical, biological. Sourcebook Project. pp. 218-224.

Devereux, P. (2004). Archaeoacoustics – Spirits in the Stones. Fortean Times, 188. p. 46.

Gibbons, J.F. . and S. Schlossman. (1970). Rock Music. Natural History. 79 (10): 36–41.

Lund, C.S. (2009). Early Ringing Stones in Scandinavia – Finds and Traditions, Questions and Problems. Reprinted from Studia instrumentorum musicae popularis I. Edited by Gisa Jähnichen.

Montgomery, A. (1956). Thermal Metamorphism of Redbeds by Diabase at Ringing Rocks, Near Kintersville, PA. Proceedings of the Pennsylvania Academy of Science. 30: 176-181.

Pontolillo, J. and J. Pontolillo (1993). Ringing Rock Sites in Pennsylvania and New Jersey. The INFO Journal. Feb 1993: 6-16.

Psilovikos, A and F.B. Van Houten (1982). Ringing Rocks Barren Block Field, East-Central Pennsylvania. Sedimentary Geology, pp. 233-243.

Sanderson, I. T. (1968). Things: Monsters, Mysteries, Marvels, Uncanny, Strange, But True. Pyramid Books. pp. 50-58.

Wheery, E.T. (1912). Apparent Sun-Crack Structures and Ringing-Rock Phenomena in the Triassic Diabase of Eastern Pennsylvania. Proceedings of the Academy of Natural Sciences of Philadelphia. pp. 169-172.

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