Crystals higher than thirty MHz (nearly >200 MHz) are usually operated at series resonance exactly where the impedance appears at its minimal and equivalent to the series resistance. For these crystals the series resistance is specified ( SMD crystals include very very little phase sound, which leads to small jitter https://telebookmarks.com/story9300407/the-fact-about-smd-crystal-oscillators-that-no-one-is-suggesting