Things that are made of or resemble crystals are crystalline. Crystalline rocks you find on the beach are glittery and reflective, with many symmetrical planes or surfaces.
A geologist will use the adjective crystalline very literally, describing crystalline chunks of quartz or the crystalline planes of a salt molecule seen under a microscope. Sometimes the word is also used to mean "extremely clear," like the crystalline prose of a short story or the crystalline forms of your striking black-and-white photography. The Greek source is krystallinos, "of crystal," from kryos, "frost."