Black Pearl is considered common and is readily found on the ground. It can also be purchased at any NPC Vendor selling Reagents.
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The core of all magic-using skills and professions, Reagents are the basic, consumable ingredients for all spell casting. Used in all principals of magic for Alchemy, Inscription, Magery, Mysticism and Necromancy. Reagents are also used by other crafting professions, but always to instill the relative magical property of the item.