Arkansas stone is a natural whetstone or oilstone cut from novaculite, which the Arkansas Geological Survey describes as a sedimentary rock composed mostly of cryptocrystalline quartz. The survey also uses the name more narrowly: "Arkansas" stone is one of two industry categories of novaculite, beside "Washita" stone. Grade names such as Soft, Hard or Black are the maker's words, not the survey's.
The Arkansas Geological Survey says the word novaculite comes from the Latin novacula, "meaning razor stone", and that Arkansas novaculite is "recognized worldwide" for whetstones and oilstones used to sharpen knives, surgical instruments and wood-carving tools.
Stone makers put the name to a second use, inside grade names: Case's pages use Soft Arkansas, Hard Arkansas and Black Arkansas, and Buck's 2026 catalog entry for its Soft Arkansas Stone names novaculite. On a maker's label, Arkansas names the rock and the grade word sorts the stones; on the survey's page, "Arkansas" is itself one category.
The Arkansas Geological Survey says novaculite for abrasives "is mined mostly in Garland and Hot Spring Counties", and it ties whetstone grade novaculite to a "triple point texture" developed by pressure metamorphism as the Ouachita Mountains formed. It links interest in novaculite oilstones to the rock being "viewed as" more natural than synthetic alternatives, a view the survey reports, not a finding on how either kind cuts. Where a particular stone was quarried is its maker's to say.
A grade word on a stone comes from its maker, and the Arkansas Geological Survey names none of them as a grade.
How Soft and Hard compare is the business of the soft vs hard Arkansas answer. The separate oil-on-a-stone answer explains the makers' lubricant instructions.