Using cerium oxide on anything with lots of silica (SiO₂) could be described as magic in the way it works on it. As you can see with this cab, the highly polished or shiny areas were highly silicated thus the sparkle. The other grey areas, perhaps hematite, are dull because they lack the silica. Also when there are separate distinct grades of hardness all mixed together in the stone you may get "pitting". Whatever the dark black mineral is on this rock it's obviously softer than the silica (7) and therefore it pits out. Take a look at the last photo where I angle the light to show it.

Really nice job on the cab and the pics are fabulous!
What is the matrix?