"...In Sight like unto an Emerald"
"The beloved disciple...saw a rainbow round about the throne, 'in sight like unto an emerald.' The emerald was Judah's stone, and was green, denoting eternal freshness and eternal endurance. It was the wedding stone of ancient oriental times."
(The Revelation Verse by Verse Study, Dr. Oliver B. Greene)
"The emerald was known in ancient times, not only for its beauty, but also for the alleged power of healing diseases of the eye."
(Universal Standard Encyclopedia)