We have a lot of blue shale on this place. In some places we have little oil slicks from all that shale. When we first moved here, I gathered all sorts of rocks from the creek to make a fire pit. The blue rocks exploded when we built our first big fire.
Note: Don't use blue oil shale to line a fire pit with.
If you look at our creek banks, you can see layers of blue shale alternating with orange iron-rich layers of sedimentary rock.
You can see the blue layer near the bottom of this pic.
The whole blue and orange thing makes me happy.
Here's a better view.
Most of the bottom of the creek bed is blue like that. After storms
have moved a lot of water through, the bottom is scrubbed clean of
algae, etc and the blue shines through.