E1572 | medium | left | play | “Emerald ID: E1572, Weight: 1.61 Carats, Origin: Colombia” Technically a perfect green should be a pure green color, but the most desirable emeralds have a slight blue color in them.
Ideally, the gem would also appear eye-clean and visibly free of inclusions. Emeralds are Type III gems however. This means being eye-clean is so exceptionally rare in emeralds that even the auction houses will take ones that have been treated for minor clarity enhancement. Nearly all emeralds have been treated to improve their transparency with a specific type of oil filling in their fractures.
While needing to be infrequently re-oiled every some-odd years, it is the most popular treatment for emeralds.
Emeralds are a variety of the mineral species beryl. Pure beryl is colorless (also called Goshenite), with the color coming from trace amounts of chromium and occasionally vanadium. In order to reach the ideal emerald green color, they also need a little bit of iron to be blue. Thankfully iron is one of the most plentiful elements in the earth’s crust.
The rarest part of finding emeralds is the coloration falling into a very specific range. Another variety of beryl is called green beryl. It sounds like it should be an emerald, but is not. Green beryl is lightly colored and regarded by gemologists and the jewelry community as a different variety of beryl from emeralds. Some individuals qualify emeralds as being colored by chromium and green beryl being colored by vanadium, but the green colors the two elements produce significant overlap. This cannot be used to differentiate emeralds from green beryl.
Emeralds are defined as being medium-light to dark. Their color saturation from grey to green also needs to reach a certain threshold, but grayish or brownish gems are not appealing next to their better colored varieties.
Tone Scale Example (Beryl – Emerald Colors)
It should also be noted that beryl can come in a rainbow of colors including red, yellow, colorless, blue, and orange. Some varieties are much rarer than others, with emeralds being one of the rarer examples.