結晶
けっしょう · kesshou · JLPT N1 · noun
crystal
💎 結 (tie, bind) + 晶 (sparkle): atoms bind into an orderly, sparkling solid
晶 is three 日 (sun) stacked, meaning bright sparkle. 結 means to bind or form, so 結晶 names matter that binds into a bright, orderly solid, which also covers crystallization.