The Whetstone artifact can be found at Fort Morn, in the central part of Sea of Núrnen.
Whetstone, Third Age
Among the millions of volcanic rocks to be found within the mountainous borders of Mordor, this stone is unique. It is a Dwarven Whetstone, used to sharpen axes, knives and swords to a keen edge that will cut through even the toughest Uruk armor or the stony skin of a Troll.
"'It's the keen edge what cuts the mountain,' as the saying goes. Whoever the stone's user was, he was most thorough in his efforts.
"Keep sharpening! You've got to hone yer axe until its edge can split one of yer beard hairs in two.
Aw, it's sharp enough to kill a Graug. Now, pass me the pipe…
'Sharp enough' ain't what the hunt's about, little brother! You've got to learn to respect the hunt. A keen blade for a clean kill. Without respect for the beast, we're no better than the Orcs. Now, let's give 'er a test…
Fer Durin, give a Dwarf fair warning when ya yank hairs from his beard!
Look, at this, Torvin! Split the hair in two! There's hope for you yet!"