Stacking things is a surprisingly difficult problem to solve. In the real world, you can just place objects on top of each other. But simulating that is surprisingly tricky, and stacking a lot of irregular objects can tax most physics systems. Each little shift in position might have a cascading effect on other rocks, but if it is too sensitive, the whole thing becomes jittery.
So here’s an approach that generates stacked tiles directly, instead of trying to simulate the physics. Presented by Adrien Peytavie, Eric Galin, Stéphane Merillou, and Jerome Grosjean at Pacific Graphics 2009, it uses a top down process that is much faster and more reliable than trying to simulate it from the bottom up.
The approach in this project specifically creates irregular tiling that avoids repetition. Many other tiling solutions have inherent repetition. Obvious repetition on something that is supposed to be natural is jarring and draws the eye, so that is a property that seems useful for other applications.