Very interesting... Thanks for your post piasa, I appreciate it! (o:
No doubt you are aware that, for suitably homogenous and well-calibrated sources, photomicrographic measurement of the depth of hydration (patination) has proved to be a fair first-order aging technique for flaked obsidian. However, since hydration rate is strongly affected by the surounding soil (pH, etc.) conditions, I have never relied on it.
But this specimen is supposedly andesite, which is so heterogenous that all patination 'bets are off'...
Thanks again!