Strong’s Greek
G4664 — smaragdinos
The entry below is Strong’s own definition (1890, public domain), and every verse where the word occurs.
σμαράγδινος
smaragdinos — pronounced smar-ag'-dee-nos
from 4665; consisting of emerald:--emerald. see GREEK for 4665
1 occurrence in the KJV.
Revelation 4:3
And he that sat was to look upon like a jasper and a sardine stone: and there was a rainbow round about the throne, in sight like unto an emerald.