I bought this stone from an antique shop in Tallinn. They could tell me nothing about it. The stone measures 1" 1/16 x 4" 6/8, or 2.7cm x 12.5cm. Thickness above wood is about 1/4" or 7mm. It appears fairly soft and lapped fast (there was a significant dishing, it came out nice and quick).
Dry color is light grey with pronounced dark grey stripes and coloration in brown, wet it shows grey with brown stripes. The slurry appears very light grey on stone, on my white sink it is a brownish grey.
The city of Tallinn had a significant german influence so there is a possibility it has some german connection.
Attachment 83026
Dry
Attachment 83028
Wet
Attachment 83027
Slurry