Does anyone here use or have knowledge of the Finnish Fylliitti sharpening stone? A famous knifemaker in FInland - Roselli - recommends this stone for sharpening his Ultra High Carbon and Wootz metal blades. I would like to have some more information on this type of stone.

From what I have been able to learn, the equivalent English word is Phyllite; this describes a metamorphic rock, derived from slate, that has a significant fraction of crypto-crystalline (my description) micaceous minerals, and a characteristic wavy or rippled surface.
Carpetsahib