Why is iridium so important to everybody that I see on YouTube. Is it something magical?
Iridium Ore is used to make the Quantum set of Armor, aswell as the Iridium Drill(the upgraded version of the Diamond Drill). First you will need to find one in a chest, and use it to be scanned so that your Mass Fabricator trough UU-Matter can produce more of them.
In FTB Infinity Evolved Expert Mode the Iridium have more uses though.
You use iridium ore to make Quantum Armour, the most powerful armour in IC2. It can be found in dungeons or produced with a Mass Fabricator. Quantum armour is extremely powerful, and makes you virtually invincible (along with other effects such as super fast sprinting and breathing underwater) while it is charged, so iridium ore is very desirable.