Crystals and load capacitance

Check out http://en.wikipedia.org/wiki/Pierce_oscillator#Load_capacitance

The load capacitance is the total capacitance seen from the two pins of the crystal looking into the circuit. So if you have a 6 pF from each leg to ground, that's 3 pF total (capacitors in series halve, capacitors in parallel add).

It's really rated for 6 pF? That capacitance could be provided by the traces and PCB layout alone, I would think. Typically I've seen more like 30 pF.

Are you sure you need a capacitor at all? 6pF and 50KOhms sounds like a watch crystal application. As was mentioned usually the IC + traces provide you sufficient capacitance (3pF per connection).

The recommendations for some of the Maxim RTC clocks is a 6pF crystal. The 6pF is supplied by the IC and traces.

Watch crystal oscillators in some MCUs have the feedback capacitors built-in. The MSP430 is one such family that springs to mind.