The hard seam makes it appear to be a coticule to me as well. A two sided barber hone would have a color only seam like a natural stone would. There is an American Hone Co. Super Punjab that looks very much like a coticule when new as one side is quite yellowish but it quickly ages to a mellow, Escher gray. These were 2 sided with a wavy seam like a natural coticule. They came with a small rubbing stone too and special instructions on NOT leaving it in sunlight as it will break down. It is a very cool hone and I'll try and post a photo later..........but, I digress, yours seems to be a coticule.

Tony