Pencil Cleavage is developed through the intersection of cleavage and bedding planes. The fractures form long, skinny pieces of rock.
This vertically dipping fault shows deformed shales in the core. On the right side of the photo slickenlines on the carbonates are seen. Bedding has been rotated to vertical. The shales are folded and fault by motion on the larger fault.
Here are some of the lava textures on Bishops Peak Mt., San Luis Obispo. The chain of dacitic volcano known as the “Nine Sisters” is associated with the shut down of subduction along the California Coast.
Today’s Friday Rocks and first gif in the series comes from Ben Melosh. Here is a folded Ultramylonite in the Pofadder Shear Zone, Southwest Africa.
Do you have an awesome picture of a rock? Email me at Timothyjsherry[at] gmail[dot]com with the picture, location, and description.