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One day, while studying a 520 million year old rock formation in western Utah, and strolling across a slope consisting of shattered shale slabs, I came across a chunk of rock with a bunch of big pyrite crystals in it, some as wide as my thumb. These were of course limonite, oxidized by sunlight, but beautiful perfect cubes. I picked the rock up, and then saw another, and another. They curved around the slope in an arc parallel to bedding. One thin layer stuffed with iron sulfide, now with water added, but laid down in an oxygen-free environment on or below the sea floor half a billion years ago. (I know this was marine, because the formation, the Wheeler Shale, is full of trilobites.) The slope of broken shale covered the solid rock from which it had come, so even though I knew where the pyrite-rich bed was, all I could find were fragments. Some I gave away to elementary teachers who had rock and mineral collections in their classrooms, some I gave to other people, and a few I still have left. I've had them for approximately 45 years, which is less than one 100,000th of 1% of the time they have existed, first under the sea floor, later in a huge mountain range, and finally shining in the Utah sun.