dīˈäpˌtās, -āz noun
( -s )
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 ) — more at optic
: a mineral CuSiO 2 (OH) 2 consisting of hydrous copper silicate and occurring in emerald-green crystals and massive (hardness 5, specific gravity 3.47)