May birthstone: emerald

How to read it

Emerald has been the birthstone for May since the 1912 list. GIA calls it "the definition of green", and the International Gem Society describes the best emeralds as an even, deep green, some with blue undertones. It is 7.5 to 8 on the Mohs scale, against diamond’s 10, and GIA gives it as the gem for the 20th and 35th wedding anniversaries.

Also searched as: birthstone for May, emerald birthstone.

Where the name comes from

GIA traces "emerald" to smaragdos, ancient Greek for a green gem.

Emerald or agate

The 1912 list settled on emerald, but older lists split. Of the eight Kunz compared in 1913, agate appears for May in five and emerald in four, counting alternates.

Where emeralds are mined

GIA says Colombia has been the source of the finest emeralds for more than 500 years, and names three mines there: Muzo, generally for darker pure green stones, Chivor for lighter, slightly bluish green, and Coscuez for slightly yellowish green. Brazil’s Minas Gerais, Zambia, Pakistan and Afghanistan are other producers.

Treatments and inclusions

GIA says emeralds are often treated: paler stones with many fractures may be dyed green, and fractures that reach the surface are often filled with oils, waxes or resins to make them less visible. The International Gem Society says emeralds commonly have inclusions that can be seen with the eye.

Emerald or peridot

The International Gem Society says the green of some peridot, an August birthstone, overlaps with emerald’s, but that peridot often has a yellowish overtone not seen in emeralds.