Are there any interesting ideas on them? Eg. how would they be controlled?
Initial artificial cells or nanobots will most likely be like our own cells and function purely on chemical signals. Future nanobots will probably be cloud intelligence linked with the brain, and far future may be swarm/cloud intelligence.
Biomass, not rocks smile silica is a bad nutrient....
With nanobots it wouldn't matter what materials you ingest. The small machines would be able to take it apart piece by piece and build other useful materials out of it.