VERY FINE GRIT SHARPENING STONE IN WALNUT HANDLED CASE - COTICULE(?)

I believe this is likely a Belgian Coticule stone. Measures 3 7/8" x 13/16" on the top. It is tight in its holder so not sure on the thickness. Gently arched wear as can be seen in the photos but a beautiful stone and holder. Very very smooth surface.