[Radio Wrangler]

I've seen some fundamental oscillators which erratically jump onto overtones and back, so an LC in a fundamental oscillator can be seen as insurance!

The main modes of a crystal can be viewed as a cluster of modes with extremely small frequency offsets between them. Oscillation seems to wander around these sub modes. They're close enough together that this may seem like angels dancing on a pinhead, if it wasn't for bits of energy seem to be left behind by mode umps, and then reabsorbed with a bit of phase drift when the mode jumps back. This seems to fit some of the small but abrupt phase umps a running crystal oscillator can do. They can run quietly for a good while, and then exhibit a group of little phase umps. Rather like the horrible popcorn noise that used to plague certain opamps. Don't worry about this unles you need to go into ultra low phase-noise oscillators at offsets in the few hertz region.

And crystals are gravity sensitive as well... turn them over and the frequency shifts, turn themback over and it shifts back. They act as microphones for rumbly bearings in cooling fans!

David