  In simulations of supercooled, high-density liquid silica we study a range of
temperature T in which we find both crystal nucleation, as well as the
characteristic dynamics of a glass forming liquid, including a breakdown of the
Stokes-Einstein relation. We find that the liquid cannot be observed below a
homogeneous nucleation limit (HNL) at which the liquid crystallizes faster than
it can equilibrate. We show that the HNL would occur at lower T, and perhaps
not at all, if the Stokes-Einstein relation were obeyed, and hence that glassy
dynamics plays a central role in setting a crystallization limit on the liquid
state in this case. We also explore the relation of the HNL to the Kauzmann
temperature, and test for spinodal-like effects near the HNL.
