Can anyone tell me about this sharpening stone

I cant find this stone anywhere online, it was my grandfather's and its at least 20 years old, probably over 30. A link to a product page or review would be so helpful, please and thank you

EDIT: I made a post on reddit with more detail

https://www.reddit.com/r/sharpening/comments/pyy8ic/hello_all_i_need_a_little_help_identifying_a/?utm_medium=android_app&utm_source=share