Old Shale... on the slant. This is the child of Old Shale Corner Experiment 1. Half of the corner spawns the new OS patterns, and the opposite miter eats them. Unlike Half Old Shale, this does use true OS repeats. It's also more diagonal than the Half OS. OS diagonal corner - increase squares the bottom corner. OS diagonal corner decrease squares the top edge.
Shown with a cast-on count of 63 stitches.