dioptase
noun
di·op·tase
dīˈäpˌtās,
-āz
plural -s
: a mineral CuSiO2(OH)2 consisting of hydrous copper silicate and occurring in emerald-green crystals and massive (hardness 5, specific gravity 3.47)
Word History
Etymology
French, probably from Late Greek dioptos transparent (from Greek dia- + optos visible, from opsesthai to be going to see) + French -ase (as in euclase)