Tungsten

Tungsten is a naturally spawning rare mineral added by Redpower2, but currently has no use. It resembles coal in block form and can only be found close to bedrock. Its very low occurrence rate makes it arguably scarcer than diamonds. You can collect the ore, but it will do nothing except take space in chests. It was added along with all the other natural resources of the Redpower2 mod because the creator, Eloraam, didn't want players to feel pressured to start a new map whenever she added new naturally generated content. While Tungsten currently has no practical purpose other than a serious source of EMC, players should save any that they come across. Its occurrence is rare and it could have considerable value in future Redpower2 updates. According to the EMC value system used by the Equivalent Exchange mod, Tungsten has an EMC cost equivilant to 2 diamonds, making it the most valuable naturally occurring mineral in Technic/Tekkit.

Trivia
In reality, Tungsten is an extremely hard yet brittle metal with an array of interesting physical properties including the highest melting point of any pure metal (6,192 degrees Fahrenheit). Because of its notable hardness, Tungsten is primarily used in the production of hard materials, alloys, and steels.