Eridium is the rare mineral in Borderlands 2 for the PC, PS3, and Xbox 360, used for augments, upgrades, and to purchase some of the most powerful weapons in the game.
If you’re in need of a lot of Eridium, then you’re in luck, because there is a spot in the game that you can go through as many times as necessary to stock up on Eridium.
In Three Horns Valley, you’ll come across a boss named Bad Maw that drops one piece of Iridium when you beat him.
Kill him, get your Eridium from him, then enter the Bloodshot Stronghold and Save/Quit.
When you come back to your game, go back to Three Horns Valley and kill Bad Maw again.
Repeat this process until you have all of the Eridium you need. It might be a slow process, but it’s reliable and worth it in the long run.

lordmaxilla September 28, 2012 at 3:08 am
Where do you use it to buy weapons?? Or how do you upgrade them?
TheDizle (site admin) September 28, 2012 at 7:26 am
There’s a merchant in Sanctuary that allows you to purchase several buffs for entire weapons groups, he’s the guy in the building with the purplish lights around it and will only open a slider window to talk to you. I haven’t found the merchant that sells weapons for Eridium though.
Jake326305 September 23, 2012 at 7:57 pm
Or you could just open up all the Lockers & Washing Machines in town of Sanctuary. Way more Iridium, WAY faster! Hope this helps you!