Are there any elements that wouldn't be useful to a self-replicating machine?

I wanna have a scene where the protagonists see the gray goo excreting human skeletons because they can't use the calcium in them for anything. But is this true? Would a self-replicating machine regard any chemical elements as truly "useless" to its goals, or would it endeavor to disassemble atoms and molecules that aren't immediately useful into ones that are? My guess is that it's not worth the extra energy to try and process atoms of one element into another until you've truly run out of other sources of that element you can easily harvest, but I'd like your opinions, as well as input from anyone who knows what useful purposes calcium might serve to such a machine.

posted about 8 years ago

Z.Schroeder‭

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