Short answers, pulled from the story.
Whetstone and sharpening stone are the same thing. The prefix "whet" comes from an old verb meaning to sharpen a blade, not from the word "wet". The term is now mostly historical; the common verb today is simply "to sharpen".
Arkansas stones are made of novaculite, a very hard natural mineral with crystal sizes of 3-5 microns. They take their name from the Ouachita Mountains in Arkansas, a noted quarrying source for this stone. Their fine crystal structure makes them well suited to the later, finishing stages of knife sharpening.
A 1000-2000 grit stone, with particle sizes around 8 micrometers, produces an edge sharper than most factory edges on kitchen knives. Coarser grits around 200-500 are used to rebuild a damaged or very dull edge, while stones in the 4000-10000 range are used for fine polishing.
The Honyama mines closed in 1967. The widespread availability of high-quality artificial whetstones with consistent particle size reduced demand for natural stone, making continued quarrying commercially unviable.
The Belgian Coticule is a yellow-gray natural whetstone quarried from the Ardennes that has been prized for its edge quality since Roman times. It forms naturally alongside the coarser Belgian Blue whetstone in adjacent geological strata, allowing two-sided blocks with a naturally occurring seam between the two layers to be produced. A specific variety called La Veinette is particularly sought after for razor honing.
A diamond plate is a steel surface coated with electroplated diamond grit used for sharpening steel tools and for flattening whetstones that have worn hollow in the middle. High-quality versions use monocrystalline diamonds set in nickel, which resist fracturing and extend the plate's lifespan. Diamond plates are available in sizes ranging from credit card to bench plate.