Radium

Generating a surprising amount of surface energy, radium is an integral part of some core components of modern technology, its also highly radioactive and can be lethal after extended contact with organic matter. This is why we wear goggles, people.

Radium is an extremely rare mineral, it will take a lot of effort to gather much of this at first. However, the fruits of that labor will not go unrewarded. A crafting resource for the Helix Armor Set that provides great protection for fighting bosses.

Gathering
Mining radium takes a very long time to mine using even an Enhanced Laser Pick.

The first biome you will encounter radium is the comet biome (The 2nd biome) and it is extremely rare find.

Bring along detonators to help access radium in the background, or mine in tunnels from an edge.

A good strategy is to wall yourself in with carried dirt prior to mining, to provide protection against most enemies that might spawn.

Radium isn't found in the earth (Dirt, clay, mud etc) it generates in ice pockets under the surface, they spawn in patches of 1-3.

Appearance
It's appearance does not change depending on the biome it is located in. It's purple color make it easy to spot in the foreground, but it is mostly found in the background and blends in with most common background tiles.