Alien crystal

Alien Crystals are items which are added to Fallout 3 in the Mothership Zeta add-on.

About
Alien Crystals come in two variations; Small Alien Crystals and Large Alien Crystals. They are commonly found aboard Mothership Zeta.

Though nominally useless, these can be sold in bulk back in the wasteland for a reasonably large amount of caps. They can also be used in The Pitt's ammo press: large crystals make 200 rounds while small crystals make 100 rounds. (needs verification)