So I was looking on eBay and I found a product complete with a nice original box
Title: Norton Abrasives Granite Hone Whet Stone Sharpener
I assume that the intention is to HONE, not sharpen on the stone. I could find almost nothing about how to use this other than a single conversation on a forum that had almost no information.
My guess is that these used to be common and as Arkansas stones came into use, the Granite hones were no longer used, but, that is a complete guess based on almost nothing.