common green ore of copper, a basic carbonate of copper having a beautiful green color, late 14c., from French malachite, ultimately from Greek malachitis (lithos) "mallow (stone)," from malakhe "mallow" (see mallow (n.)); the mineral traditionally so called from the resemblance of its color to that of the leaves of the mallow plant.
"bright green precious stone," c. 1300, emeraude, from Old French esmeraude (12c.), from Medieval Latin esmaraldus, from Latin smaragdus, from Greek smaragdos "green gem" (emerald or malachite), from Semitic baraq "shine" (compare Hebrew bareqeth "emerald," Arabic barq "lightning").
Sanskrit maragdam "emerald" is from the same source, as is Persian zumurrud, whence Turkish zümrüd, source of Russian izumrud "emerald." For the unetymological e-, see e-.
In early examples the word, like most other names of precious stones, is of vague meaning; the mediæval references to the stone are often based upon the descriptions given by classical writers of the smaragdus, the identity of which with our emerald is doubtful. [OED]
Emerald Isle for "Ireland" is from 1795.