One of the strangest natural wonders of Montana are the so-called Ringing Rocks outside of Whitehall. When struck with a hammer, the rocks will ring like a bell or even a gong. You can hear their perfect tones reverberate for some time after each strike.
Curiously enough, however, if you remove one of the rocks from the pile and then strike it with a hammer, it will not ring. This suggests (although we're no geologists) that it's not the composition of the rocks, or rather, not just the composition, that causes the ringing, but the way they are set on top of one another as well.
The ringing rocks are situated on a "pluton", an igneous intrusion of volcanic rock under the surface, left by a volcano that erupted 76 million years ago. The iron content of the rocks is 7% or less, suggesting that iron is not a significant source of the ringing.
In fact, science has not succeeded in explaining why the ringing rocks ring. So we'll suggest our own answer: aliens!
You can see even in this video that sometimes hammer strikes do not produce a ringing, but when they do it is a beautiful, clear tone.
See the whole video below, and let us know if you have any theories as to what is causing the ringing!