Have you looked at Project Vesta? It's a proposal to create olivine beaches around the tropics to boost sequestration due to rock weathering. I think it's somewhat disputed because rock weathering in a surf happens at a different rate than normal, but their analysis is that if "only" 2 percent of tropical beaches were covered in olivine the weathering would counteract current emissions. I can't tell how serious this proposal is and am curious to hear from anyone who knows more about this process.

https://projectvesta.org/