They can range from olive green to a pure grassy-green color. As supply is so low, green zircons are usually only sold by gem ...

Emeralds, another popular gemstone, derive their lush green color from trace amounts of chromium or sometimes vanadium.

Unlike the colorless aluminum ion, the chromium ion absorbs blue and green light when surrounded by the oxygen ions. The red light is reflected back, so that’s what you see in rubies.