Incendicite is a rare metallic ore that is highly sought after. The only known source on Azeroth is in dwarven territory, from the cave system known as Thelgen Rock in the Wetlands.
The most notable property of incendicite is that it's explosively volatile when exposed to a spark, so it cannot be mined with regular steel tools. Even accidentally dropping regular steel onto incendicite can be enough to set off a chain reaction.