Speaking of which, on resource gathering with Plasma Grenades:
They do work on resource pillars, gold balls, copper floating eggs, etc.
They don't work on resource crystals, or the rare mats you destroy rather than collect (sac venom). Will just blow them up.
They work great for getting iron and carbon from rock/flora. Oneshotting trees with them is fun.
Yeah Plasma grenades are probably the best for getting Iron. While they do work on resource pillars, it's generally more efficient to just mine with your laser, especially if you have upgrades to your beam. In fact, if you upgrade your grenades with the bigger impact radius, it will blow huge chunks into resource pillars but you'll still be getting the same amount of materials. You'll be wasting the resource if you plan on mining most or all of it.
They make the best offensive weapon hands down though.