Thankyou for posting this. Sometime ago a member here posted about a blue Arkansas stone, and he described it as being more like a strop in use, as opposed to a hone, due to it's smoothness. I haven't been able to find the post since, and I've asked a number of companies and individuals about such a stone, but no-one had ever heard of such a stone. So at the very least you have something that seems to be rather rare, and potentially, very fine.

Kindest regards,
Alex