epidote

noun

hydrous calcium aluminum iron silicate, a yellowish-green to black mineral, Ca(AlFe)SiO(OH), found as monoclinic crystals, grains, or masses and sometimes used as a gem

Etymology: Fr épidote < Gr epididonai, to give besides, increase < epi-, over + didonai, to give (see date): so named by R.-J. Haüy (1743-1822), Fr mineralogist; from the enlarged base of some of the crystal forms