We have experimentally studied the thermal behavior of Si2O3, the metastable condensate from SiO vapor. Si2O3 and its successor, amorphous quartz, have previously been shown to have infrared spectral features similar to somme that appear in the spectra of grains in oxygen-rich circumstellar regions. Thermal annealing experiments show that only one Si2O3 decay process operates over the range 750K<T<1000K. This process is a unimolecular disporportionation. The rate of this transformation can be expressed as k(hr1)=109 exp(-40 kcal/mole/RT). Using this rate constant we find that a significant fraction of freshly nucleated circumstellar grains can survive passage through a typical circumstellar shell virtually unaltered in structure. We emphasize that this is only the first in a series of laboratory experments intended to study the metamorphism of newly condensed circumstellar material ejected into the interstellar medium. Grains similar to these might have been incorporated into the primitive solar nebula provided that they could also survive passage through the general interstellar medium.