Small crystal (left) and large crystal (right)
Alien crystals come in two variations; small alien crystals and large alien crystals, possibly a form of alien currency. They are only found aboard Mothership Zeta on some aliens, lying on some tables or shelves where they are especially hidden among the alien artifacts the player cannot pick up.
They are weightless, and have values of 10 and 20 bottle caps respectively. They have no other use besides as trade items, Rock-It Launcher ammunition, or as a house decoration.