Actual slate placed as shims for the main beam at the foundation beam pockets. Same house had the support screw jack columns placed upside down. The “screws” were not locked in place, as required. Unable to determine if footings were placed for the columns.
I would report that small pieces of slate may crumble with structural loads over time. Recommend steel shims. Small wooden shims will compress over time.
If stone is to be used for structural support it must be large pieces with a lot of bearing surface. How big a piece and how much bearing surface? Ask an engineer.
You are right, I did recommend steel shims. Posted the photos because I doubt if inspectors will see slate used for this purpose. I know that I was quite surprised.