Portable x-ray machine. The pocket-sized hand-held battery-powered ones are only 37,500 dollars (batteries not included, available separately at 275 dollars each, takes four).   Just kidding!  In many cases there's a clue on the outside of the concretion. If you've looked at the fossil crab prep threads you'll know what I mean. In other cases, like Mazon Creek concretions you can't tell most of the time. You just have to freeze and thaw them until they crack open. Some that contain amm
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