Here is what I think is the mining algorithm:
Rocks can be standard or "huge" (except metal rocks that are only standard).
A standard rock has a basic capacity of 50 chucks. A "huge" rock has a basic capacity of 150.
Each time you use your pick, you get between 3 or 10 chunks. Before the reset, I believe it was between 4 and 10. It does not seem that the number of chunks depends on your mood.
When there is less chunks still available in the rock, you still get between 3 and 10 rocks. This is the reason why, from a full standard rock, you get between 50 and 59 chunks, and from a huge rock between 150 and 159.