If the mineral quartz has a specific gravity of 2.7, what is its density?
I think it would be rather high in the ultrasonic range. It would depend on the size of the grains. Look up the speed of sound, v, in quartz or similar rocky material. The wavelength at the lowest resonant mode would be about twice the grain size, a. This will let you compute the approximate resonant frequency using f = v / λ = v / (2a)
