ep·i·dote (ěp'ĭ-dōt') n. A lustrous yellow, green, or black mineral, Ca2(Al, Fe)3(SiO4)3OH, commonly found in metamorphic rock.
[French épidote, from Greek epididonai, to give in addition, increase (from the greater length of its crystals compared with those of related minerals) : epi-, epi- + didonai, to give; see dō- in Indo-European roots.] ep'i·dot'ic (-dŏt'ĭk) adj.