It's even better than that. You can grind metal oxides that form a sizeable fraction of Earth's crust and are relatively easy to extract into a sort of "dust" o

It's even better than that. You can grind metal oxides that form a sizeable fraction of Earth's crust and are relatively easy to extract into a sort of "dust" or "sand" that will actively sequester carbon out of the air, with no further energy input needed. Not silicon-based rock, though,