Kalaxian Crystals are found growing in a parallel universe during the episode "Ricksy Business". Morty, Abradolf Lincler and Nancy are sent out by Rick to collect them. Rick tells them that the crystals are what they need, although he never states what it is they need them for, but Morty assumes that Rick meant that the crystals would take them home.
Upon returning with them they find out they are in fact some sort of drug, as Rick cuts it up and snorts it claiming it to be a powerful but short lived high.
The blue hue that Rick's eyes acquire after snorting the crystals is likely a reference to the mind-expanding drug Melange (spice) from the Dune series of novels (and films).
Trivia
- The Kalaxian Crystals are very similar to many drugs, as the crystals give you a good sensation and they are often grown or thrive in the wilderness. However the crystals seem to be much more potent than other drugs but last a much shorter time than any other drugs.