Joe, I think that crystal is a very pure form of glass, and it's often very thin when used for glasses. I sort of have a clue about the physics, but Homeless, I would love to hear an explanation. Pure tone=frequency. The note causes a sympathetic vibration in the glass, and when it becomes great enough, the glass just vibrates itself to pieces? Sort of what happens when you hit one G string on a hammered dulcimer (or other instrument) and all the G strings vibrate? Or is that completely different?