On Merx, the "common" metal is now called Ferroxyde. Solid, but easily transformed in a forge, it will be useful to make the first tools and weapons. Besides, Ferroxide ore can be found on the surface, in the scattered boulders in the plains. If an object needs to resist to high temperature, it will be better to design it using some Calorium, that can be found below the surface, in the yellow sandstone. Finally, in the chalky rocks, you will find some Electrum, that is mostly used in electric items.
Different gemstones also illuminate Merx caves: Laserite (red) is used to create laser ammo and any other laser-involved objects. Crystaline (white) is a hard gemstone used to cut and crush, in the gauntlet recipe, for example, and Explodine (orange) will be used in different explosive recipes.
Istara also contains some useful metals: The Steeltanium is harder than the Ferroxyde, and will allow you to build more resistant objects whereas the Carboflex, that is light and flexible, is a great natural and recyclable alternative to plastics since the last drops of petroleum have been used a few centuries ago, in the Aevian System. Istara's gemstones are the Concentrite (yellow) that improves the properties of whatever it is mixed up with, the Reversine (purple) that reverses some effects, and the Silicine (blue), a semiconductor material that is used in most electronic circuits.
Of course, lots of other resources are used in the crafting system: Plants, like Mandragoras, Cotton or Fire flowers, Mushrooms, Fur, or even Goo, a slimy and sticky material created by spiders to protect their eggs...