Crystal

A large Cyrstal

A crystal is a regularly ordered solid mineral.

Data experimented with producing vibrations in a crystal by means of graviton pulses which Doctor Kila Marr later compared with tapping a crystal goblet. This technology was later implemented to make contact with the Crystalline entity and was later used by Dr. Marr to kill the creature. (TNG: "Silicon Avatar")

Captain Jean-Luc Picard kept a small transparent crystal on the desk in his ready room aboard the USS Enterprise-D. He often played with the small stone when he had to make an important decision. (TNG: "Where Silence Has Lease", "A Matter of Time")