eBay + insomnia + credit card + vodka resulted in a hone arriving at my door. On initial inspection, oil soaked carbo, great. I soaked it in Dawn dish soap and warm water for several hours then scrubbed it. Resulting in this:
Hmmm, maybe.
The imperfections appeared natural, but seem too hard to be a slate, harder than the coticules I've played with. I have zero experience with lapping slate hones.
eBay "silt stone"