gems, beryl, emerald, Afghanistan, Brazil, Colombia, Zambia, Madagascar, China, Pakistan, Zimbabwe, inclusions

The French chemist N.L. Vauquelin (1763–1829) discovered chromium (Cr) in crocoite (PbCrO₄) from Beresov, Russia, and beryllium (Be) in emerald from Colombia more than 200 years ago. He determined the correct chemical composition of emerald and demonstrated that the difference between beryl and emerald was due to the presence of the coloring agent chromium. Today, emerald is defined by Schwarz and Schmetzer (2002) as “yellowish green, green or bluish green beryl—natural or synthetic—which reveals distinct Cr and/or vanadium (V) absorption bands in the red and blue-violet ranges of its absorption spectra.” Emerald is one of the most valuable gemstones. It is much rarer than diamond and can command a value thousands of times greater than gold. In the colored gemstone market, color is more important than clarity or brilliance in determining the value of an emerald. The green color of emerald arises from the unique geological conditions of its formation in contrasting environments. This article reviews, using state-of-the-art data, the crystal chemistry and formation of emerald, highlighting its paradoxes, as well as the geology of economically significant emerald deposits worldwide, comparing their origins, similarities, and differences.