I think the analysis I saw was that it's energetic enough that the entire mining + grinding + "burning" process is energetically favorable. Which I found pretty

I think the analysis I saw was that it's energetic enough that the entire mining + grinding + "burning" process is energetically favorable. Which I found pretty astounding, but I think that points more to the incredible efficiency of mining and industrial processes than anything. I think that was also at elevated temperature in a carbonic acid solution, so basically the fastest possible "weathering".