This incredibly well-preserved 2.2 cm jaw of a fossil mammal from the Pleistocene is now writ in turquoise. These trickle out of the desert from time to time, found in handfuls by the lucky prospector. What happened is that copper-rich solutions flowing through the fossil beds, from nearby copper deposits, altered the bone, or the fossilized bone, to turquoise. These replacements are generally complete all the way through, and are invaluable to researchers as they preserve superb bone detail internally as well as externally. This is one of the finer examples I have seen because it has a complete lower jaw (of a marmot-like rodent, I am told), and the aesthetics are good.