The word “Novaculite” is derived from the Latin word “novacula”, which means “razor stone” and is essentially a metamorphic, recrystallized, variety of Chert composed mostly of microcrystalline quartz that is found in the found in the Ouachita Mountains of Arkansas and Oklahoma and in the Marathon Uplift of  Deposited in the Devonian Period and the early Mississippian Subperiod some 410 to 325 million years ago and subjected to uplift and folding during the Ouachita orogeny of the Atokan Epoch (early Pennsylvanian Subperiod), Novaculite is a very tough stone that is resistant to erosion and thus, the various layers of Novaculite stand out as ridges in the Ouachita Mountains. Thus, due to both its availability and its composition, it has been mined since ancient times for use as arrowheads and spear heads as well as in more modern times for use as sharpening stones.
One of the most important factors in determining which sharpener is best for you is the type of knives you’ll be sharpening. There is a difference between styles of knives that will help you understand what to look for in a knife sharpener. To have a better understanding, see this guide on the differences between Euro/American and Asian knife blades.
To take off the fine scratches and the burr left by coarser stones, and polish the surface, one can use stones starting around 2000 grain. Above that there is theoretically no upper limit, but at the same time stones above about #10000 provide no measurable practical improvement in the edge. It is also interesting to note that above #8000 grit, there is no Japanese measurement standard. With all the stones labelled as having a finer grit, one simply has to take the manufacturer’s word for it.