Here is my special stone. It's branded extra fine faintly on the side.

https://youtu.be/NO4xn0h_2g4

Extra fine stamped la lune

https://youtu.be/4UAshsjWGog

The special stone is just more difficult material to use. It cuts even faster than the purple, I don't feel it has quite as much consistency. It's slightly more porous. Mind you, it's an ultra fine rock regardless, but I wouldn't recommend it over the purple ever.