Crystal Oscillator with OP AMP, or Oscillator circuit built with Crystal and Op Amp
According to TI,


  Op amp oscillators are restricted to the lower end of the frequency
  spectrum because op amps do not have the required bandwidth to achieve
  low phase shift at high frequencies. The new current feedback op amps
  are very hard to use in oscillator circuits because they are sensitive
  to feedback capacitance. Voltage feedback op amps are limited to a few
  hundred kHz because they accumulate too much phase shift.


The point being that even if you have an op-amp with 10 MHz or even 100 MHz GBW, because of its multi-stage design, it will very likely have too much phase shift at high frequencies to be usable in an oscillator circuit. Which isn't to say there isn't somewhere out there some device and circuit that could achieve an 8 MHz oscillator, but the odds of it working with any op-amp you pull out of a drawer are pretty low.

In any case, many oscillator designs are available using a single transistor as the gain element. There's no need to use an op-amp when a single transistor will do.