Clock Generation from Oscillator
If you're not too fussy about duty cycle or jitter, a buffer with a Schmitt-trigger input will convert the sine to a square, assuming correct biasing and sufficient amplitude.

If you are fussy about those things, then use a PLL with a post-divide, which can give you perfect symmetry and also remove some jitter in the process. (Search for 'jitter cleaner PLL'.)

I'm going to assume you don't care about skew. If you do, speak up.