Grindstones are Weaponsmithing Assets that can be acquired as necessary components for completion of a number of rare Weaponsmithing tasks (levels 14-20) and/or as optional components in Rare tasks that will improve the chances of producing a higher tiered weapon.
A [Worn Grindstone] may be purchased for 1 from M'tari Prin'tal in Protector's Enclave (North corner of the Seven Suns Coster Market). Grindstones of higher tiers may be acquired from [Professions Booster Pack] and asset packs purchased in the Zen store. Grindstones are not bound and may be traded on the Tarmalune Auction House or transferred between players.
A task requiring a Grindstone as an asset will take any tier of Grindstone in its slot. Higher tiered Grindstones serve only to improve chances of producing higher tiered results.
At Profession Level 3, 4x [Iron Grindstone] can be upgraded to produce a [Steel Grindstone].
At Profession Level 4, 4x [Steel Grindstone] can be upgraded to produce a [Mithral Grindstone].
There is no task that will allow [Worn Grindstone] to become an [Iron Grindstone].