Wolframite

Wolframite is a very rare basic material with the appearance of yellow and green cube-like chunks.

Source
Wolframite can be found here:
 * Desolo
 * Calidor
 * Trade Platform
 * 2 Wolframite for every 3 Scrap, up to 4 total

Uses
Wolframite can be used to craft the following items:
 * In Smelting Furnace
 * Tungsten

Trivia
Wolframite deposits are shaped similar to real bismuth.