The science of ringing rocks - what causes the ringing sound ?

General Questions
#1

I came across this youtube video where the subject rocks are shown. The guy on the video claims that the sound is due to the high amount of Iron in them, which Wikipedia says its not.

Here is the wikipedia link.

I can find plenty of geological references as to how these rocks formed. But I am not able to understand what gives these rocks the “ringing ability”. Wikipedia claims “Despite the broad public interest in the ringing ability of the ringing rocks there has not been any actual scientific studies to identify the source of the phenomenon.”

Is that true ?

#2

The first thing that struck me is that it sounds like the sort of ringing that you get from ceramics. some rocks (in particular metamorphic ones) are essentially natural ceramics. The Wikipedia article states:
Although the sound is often described as metallic, it is most likely due to a combination of the density of the rock and a high degree of internal stress. The sound can be duplicated on a small scale by tapping the handle of a ceramic coffee cup.

#3

I visited the ringing rocks east of Butte, Montana on an igneous and metamorphic petrology field trip and the professor said that, yeah, we don’t really know exactly why they ring. Apparently every so often she gets a grad student who tries to figure it out, but (at least as of 7 years ago or so when I took the class) nobody had really proven anything. The wiki article mentions a professor back in the 60’s tried to figure out the Pennsylvania ones and came up with a theory about internal stresses in the rocks, which is as good a guess as any at this point.

I’ve always heard that the rocks don’t ring if they’re removed from their original position, suggesting it has something to do with how the boulders are piled up. The wiki article says that’s a myth, but my old professor seemed to think it was true so who knows. FWIW, at least at the Montana one only boulders that are touching other boulders ring. There’s individual boulders of identical composition off to side of the pile that don’t ring.

#4

You’ll want to see the 1972 comedy *What’s Up, Doc? * This is a running gag.

#5

Their shape and the configuration of their supports would have been my first guess. A roughly spherical stone embedded in the dirt isn’t going to make any amazing sounds, but if you have something with a high aspect ratio, and you support it somewhere near its natural vibrational nodes - like these steel bar chimes - then the only reason it wouldn’t ring is if there’s a high degree of internal damping, like plastics.

In the OP’s video, some of the stones ring nicely when struck, and others don’t; since they are probably all have roughly the same composition, it seems likely that comes down to the geometry of the stone and how it’s supported. Many of the stones in that video seem to have a relatively flat and long geometry, so I suspect it just comes down to finding one that’s supported in a way that allows it to vibrate.

#6

Glassware rings, and contains no iron. So, that settles the question, I guess.

#7

Seen it with various types of boulders: limestone, hard ultramafics, quartz. The boulder has to be very hard, with no soft portion or fracture. It rings because of the force transmitted through, causing the whole thing to vibrate.

#8

This wonderful!

[QUOTE]

The only instrument of its kind in the world… this is a lithophone made from Michigan’s State Stone, the Petoskey Stone. The Petoskey stone is a fossilized colony coral from the Devonian Age… 350 million years ago it was a living organism, a hexagonaria percarinata. This single octave diatonic instrument was made by musician and edutainer, Tom Kaufmann. For more information, go to http://www.tinkertunes.com/Lithophones
[/QUOTE]

#9

Agreed. some of the larger, more knobbly flint nodules here in the south of England make a sort of ringing sound when struck.