The particles in a rock are constantly in motion. However, a rock does not visibly vibrate, why do you think this is the case?

This is because every solids particles are always vibrating in place because the particles are so tightly packed. Liquid particles Are not vibrating as much because it is not that tightly packed. It is much more free flowing than a solid particles but not as much as a gas particles. a gas particles do not vibrate because that are flee flooding flowing

Two reasons:

Particles are too small to see with the naked eye.

also, the amplitude of the oscillations are so small that no one can see them