Greetings from Hot Springs, Arkansas. Nancy and I have had a wonderful week of digging quartz crystals. The truck is now much heavier, and we are tired but delighted. It was very hard to decide what to do for this week's experiment. I thought about another experiment with retinal fatigue, since all the digging in red clay left us seeing everything with a green hue. I also thought about revisiting the fact that you cannot identify a diamond by cutting glass. The quartz crystals we are digging scratch glass very easily. I wound up deciding on an experiment that helps explain why the crystals are here.