We all know that rocks and stones have been around millions and millions of years. They last for ever almost. That's why we build walls with them, right?
But we wallers also are well aware that some kinds of stone material are just pretending to be stable. Stone may look perfectly good to use, but sometimes it isn't.
Even if the stuff looks well aged, and doesn't appear to have changed its composition or physical appearance in decades, some of it will let you down the first chance it gets. Even if its been lying around on the ground docile, seemingly untouched by the elements for years and years - actually it has an agenda.
The stuff is just waiting for you to put it in a wall. Then, almost immediately it starts to fall apart, separate into pieces, break up, fragment, decay, deteriorate, degenerate, decompose, rot, molder, perish, crumble, spall, chip, peel off, flake, blister, exfoliate, shed and disintegrate.
( btw. that's not my wall, above)