Node Types
Adamantite ore comes in two different node types. Regular nodes display as "adamantite vein" when you mouse over the node. Higher-gain nodes are called "rich adamantite veins" when moused over. You'll see the regular veins in lower-level zones as you move through the Outlands area, but the rich veins are placed in the more challenging zones in this region of the game world.
Mining Equipment
You cannot mine adamantite until you have a mining skill of 325 for regular veins and 350 for rich veins. You do not need any additional special equipment for mining this ore other than the mining pick. Your farming time increases significantly when you use a flying mount, especially an epic flying mount, to get around the adamantite mining zones. You move from node to node quicker because you avoid monsters on the ground. Some nodes are only accessible to flying mounts as well.
Nagrand
Nagrand in the Outlands has a high concentration of adamantite nodes, both regular and rich, compared to the other zones in the area. Nagrand's monsters are in the mid-60s, so you must be capable of defeating monsters in this level range to access all of the zones. Most of the adamantite ore is found along the rocky perimeter of the zone, although a few nodes are found within the cave subsystem in the middle of Nagrand.
Other Areas
Blade's Edge Mountains and Netherstorm have high concentrations of adamantite ore but the mining difficulty is higher than Nagrand. You need a flying mount to get around most places in both zones and the monster levels rise to the high 60s. The ore deposits are also spread out throughout the zones instead of being concentrated in the perimeter or one central area.