This site:

http://uk.ardennes-coticule.com/index.asp?id says (inter alia)

"History tells us that, whetstones have been mined in the Belgian
Ardennes since 1625."

"The stones are mined from approx. 480 million year old, almost soft,
grey-yellow sedimentary rock built up from clay and volcanic ash. During
regional metamorphosis a reorganisation of contained minerals has taken
place. Many of the minerals disappeared but importantly some appeared
namely quantities of Spessartit Garnet crystals."

However, people using cutting tools have always shown the greatest
interest in good sharpening stones.

Pliny the Elder, in Naturalis Historia (77-79 AD) says:

CHAP. 47. WHETSTONES.

We must now pass on to the stones that are employed for handicrafts,
and, first of all, whetstones for sharpening iron. Of these stones there
are numerous varieties; the Cretan stones having been long held in the
highest estimation, and the nex: best being those of Mount Taygetus, in
Laconia; both of which are used as hones, and require oil. Among the water-
whetstones, the first rank belonged to those of Naxos, and the second to
the stones of Armenia, both of them already28 mentioned. The stones of
Cilicia are of excellent quality, whether used with oil or with water;
those of Arsinoe,29 too, are very good, but with water only. Whetstones
have been found also in Italy, which with water give a remarkably keen
edge ; and from the countries beyond the Alps, we have the whetstones
known as " passernices."38

To the fourth class belong the hones which give an edge by the agency of
human saliva, and are much in use in barbers' shops. They are worthless,
however, for all other purposes, in consequence of their soft and
brittle nature: those from the district of Laminium,81 in Nearer Spain,
are the best of the kind.

We don't have to wait for the 18th century!

    BugBear
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