The amulet can be purchased from Lhara, the Darkmoon Faire Exotic Goods vendor in Elwynn Forest (Alliance) and Mulgore (Horde). The Darkmoon Necklace costs 5 gold and is available to buy anytime ...

Trinket Requires Level 50 Equip: Chance on spells and attacks to summon a sandstorm that circles you, dealing 0 Nature damage to targets it passes through.