Emerald is of the silicate class of minerals, categorized as a "beryl." Beryls (Be3Al2(SiO3)6) are clear in their pure form, but often contain impurities which provide the mineral with varying coloration. The beryl family includes pale blue aquamarines, pink morganites, golden heliodors, red beryls, and pale green beryls. Beryls are silicates which comprise the largest class of minerals, yet Emeralds are only a very small fraction of this class.

This is because Emerald crystals are formed in metamorphic rocks, whereas other beryls grow in pegmatites. Metamorphic transformation generally limits the size of Emerald crystal formation, making them even rarer in larger sizes. Emeralds derive their green hue from minute traces of chromium locked within the stone's cyclosilicate crystals - the same Midas element which gives rubies their fiery redness. "With less than one percent chromium (or vanadium), an Emerald's crystal lattice passes the green portion of white light while absorbing the red and blue."

Emeralds are found in several places on the planet. Without a doubt, the finest Emeralds come from the top three Colombian mines: Muzo, Chivor, and Cosquez. Emeralds of varying (but generally inferior) color, clarity, and quality are also mined in Brazil, Pakistan, Afghanistan, Madagascar, Nigeria, Russia, Zambia, and Zimbabwe.

Colombian Emeralds set the color and quality standards for Emeralds. Additionally, most of Colombia's gems are cut within the country. Fine Colombian Emeralds enjoy a rarity which places them among the" highest investment values of all gems." Emeralds are weighed in carats (not to be confused with karats, which refers to the purity of gold), with one carat equaling 1/5 gram, or 1/42 ounce. Because of the relatively low specific gravity of Emeralds (SGE = 2.72), Emeralds are physically larger than similarly weighted diamonds or rubies.