Can anyone help me identifying this rock and describing it? Saw this today while driving.
Sorry, but there just isn't enough detail in this photo, There are dozens of possibilities. A close up photo of a freshly-fractured unweathered surface would help. That's why geologists carry hammers and a hand lens. Even a good photo isn't necessarily diagnostic. The standard approach is to cut a thin section and analyze it under a polarizing microscope. Even experienced geologists can't always identify a rock just from looking at a hand specimen or field exposure.
This looks like shale, A type of rock formed by sediment layering of Ash and clay. But could be slate a metamorphic reworking of shale. The only way to tell is chemical composition of this rock but a simple test is to hit it with a hammer. If it breaks easily into brittle pieces than it is shale if it is hard to break, meaning you need to apply a lot of force, and breaks into smaller version of the bigger rock than it is slate. Hope this helps The left picture is shale and the right picture is slate.