Rubstone

Sharpening stones, water stones or whetstones are used to grind and hone the edges of steel tools and implements.

Examples of items that may be sharpened with a sharpening stone include scissors, scythes, knives, razors and tools such as chisels, hand scrapers and plane blades. Though it is sometimes mistaken as a reference to the water often used to lubricate such stones, the word "whetstone" is a compound word formed with the word "whet", which means to sharpen a blade, (derived from Old English hwettan, from Proto-Indo-European *kʷēd-, "sharp") not the word "wet" (OE wǣtan, PIE *wed-, "water"). The process of using a sharpening stone is called stoning.

Sharpening stones come in a wide range of shapes, sizes and material compositions. Stones may be flat, for working flat edges, or shaped for more complex edges, such as those associated with some wood carving or woodturning tools. They may be composed of natural quarried material, or from man-made material.

The Roman historian Pliny described use of several naturally occurring stones for sharpening in his Natural History. He describes the use of both oil and water stones and gives the locations of several ancient sources for these stones.

The use of natural stone for sharpening has diminished with the widespread availability of high-quality, consistent particle size artificial stones.

As a result, the legendary Honyama mines in Kyoto, Japan, have been closed since 1967. Belgium currently has only a single mine that is still quarrying Coticules and their Belgian Blue Whetstone (BBW) counterparts.

...
Wikipedia