It's a function of size. Tuning fork crystals generally have frequencies in the range of a few tens of kilohertz (generally 32768 Hz). Quartz discs vibrate at

It's a function of size. Tuning fork crystals generally have frequencies in the range of a few tens of kilohertz (generally 32768 Hz). Quartz discs vibrate at many megahertz. A tuning-fork like structure that oscillated at 100 MHz would be far to small to easily manufacture. ------ One fun note: crystals like this are used for measuring deposited material in vacuum processes like PVD [1] or similar [2]. The crystal is exposed inside the vacuum chamber where it will be deposited on at the same rate as the target, and the change in frequency is a direct function of the mass (and therefore thickness) of the deposited material. Eventually, the exposed crystal has to be replaced as it no longer oscillates properly. 1: https://en.wikipedia.org/wiki/Physical_vapor_deposition https://en.wikipedia.org/wiki/Physical_vapor_deposition 2: https://www.semicore.com/news/72-thin-film-deposition-control-quartz-crystal https://www.semicore.com/news/72-thin-film-deposition-contro...