Feltrite Crystals are miscellaneous items featured in RAGE. The crystals are shards of a previously unknown element that came to Earth with the 99942 Apophis asteroid. In an ironic contrast to the destruction wrought by the asteroid, Feltrite is a potent energy source, and is highly valued to raider tribes and settlers alike.
The crystals can be sold to vendors for $25, but can also be traded to Jacob in the "Second Chance" bar in Wellspring during the quest "Finding Feltrite". In exchange for 20 shards, he will give Nicholas Raine a device that accelerates his Defibrillator's recharge rate.