Updated for patch 4.3.
Obsidium Ore is one of the newest ores released with Cataclysm, along with Elementium and Pyrite. Obsidium is a normal ore (unlike Pyrite which is a rare spawn out of Elementium Ore nodes). You’ll need to have a mining skill level of 425 before you can mine this ore. If you are trying to mine Obsidium Ore for gold you might be interested in learning better ways to make gold as in this Gold Guide. Keep in mind that while Obsidium Ore will sell good on the Auction House, since it’s a new high level ore, there will probably be a higher demand for Pyrite and Elementium because they are even higher level ores.
Obsidium Ore in Mount Hyjal
Below you’ll find a mining route map for Obsidium Ore. I like Mount Hyjal for farming Obsidium Ore because it is not underwater, other options at this level with leave you with lots of underwater farming options. I find leveling or farming to be easier in this zone than the others partly because it doesn’t force you to swim around to collect ore. If you decide that you don’t like this route below you are always welcome to try out Vashj’ir but remember you’ll have to mine underwater.
If you’re looking for information on Leveling your Mining see my WoW Mining Guide.