Alien crystal

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

They come in two variations; Small Alien Crystals and Large Alien Crystals. They are commonly found aboard Mothership Zeta. it is possible they may be used in future fallout 3 expansions, or maybe something someone has not discovered yet, ( schematics ) ???

Trivia
The Alien Crystal could be a slight reference to the intro from the original Half Life, in which the scientist protagonist Gordon Freeman inserts a similar Alien Crystal recovered from the boarderworld Xen into a machine, causing an inter-dimensional rift to open, spawning an alien invasion.

Alien crystals appear to have no useage, but have value and weigh nothing. (much like pre-war money)

Maybe it's Alien cash?