I was walking on a reef in northern Italy near Genoa. (44.3230136N, 9.1462828E) The rock was composed of rocks of varying sizes, colors and shapes held together by some kind of a seemignly softer substrate. The substrate was still rock-hard on touch, but I was able to break some of the smaller rock out of it. (The photos below will say it best.)
The reef had several "splits" that ran across its whole length. These were white in colour and, I think, were composed of quartz. Interestingly, these splits ran straight through both the substrate and the rocks as if someone sliced the reef with a laser.
I would like to know how these formed. I imagine high pressures and shear forces were at play but I still don't understand how it's possible that the splits don't go around the rocks (at least the smaller ones) but straight through. Especially if I assume the rocks are harder than the substrate. But that might not be the case?
See the photo captions for more details.
Sorry, for not calling things by their proper names. I'm no geologist so this questions doubles as an identification one. I guess.