Spellstones

A Spellstone was a Warlock conjured item. Originally a pseudo-relic that occupied the off-hand slot and then later the wand slot which allowed warlocks to dispel all magical debuffs on themselves and increasing spell critical strike rating, Spellstones were much like Wizard Oils that are applied to the Warlock's melee weapon after the Echoes of Doom Patch. A single use of Create Spellstone (which uses a Soul Shard as a reagent) will create a Spellstone with 5 charges. It should be noted that unlike the warlock's Healthstones and Soulstones, Spellstones were not considered conjured items and thus did not disappear after being logged out for more than 15 minutes. Each charge could be only used on the weapon of the warlock who created it, and had the following effects:
 * Increase periodic spell damage by 1%
 * Improve spell haste rating by 10/20/30/40/50/60.

As of patch 4.0.1, Spellstones can no longer be created. They may still exist in inventory, but cannot be used.

Tactics
As of Patch 3.0.2, Firestones and Spellstones have replaced Superior Wizard Oil (since Wizard Oil can not be applied to weapons with an Item Level higher than 165) as the preferred temporary weapon enchants for warlocks. Firestones are best for deep destruction specced warlocks, whereas spellstone is better for demonology (with the Master Conjuror talent) and affliction.