What has caused this slate problem?

What has cause this slate to fail?

mineral inclusion-1 - Copy.JPG

mineral inclusion-1 - Copy.JPG

mineral inclusion-1 - Copy.JPG

I don’t see slate roofing in this area so my answer will be a guess. Looks like spalling caused by moisture infiltration and freeze thaw cycle.

We don’t see slate around here either but I wold guess rusting iron content, in the slate, expanding and staining downward.


I see tree branches.

I’m willing to bet that there was something hanging over this roof that was rusting away.

Larry was close… it’s called a “mineral inclusion” and it’s a mineral impurity of some kind. Since this one is bleeding redish, iron is probably right.