How to tell whether an emerald is natural or lab-grown

Three separate categories travel under the name emerald, and only one of them is what most buyers think they are getting.

Natural

Formed in the ground over geological time. Almost always includes inclusions, and almost always oiled. This is what a Colombian emerald means.

Synthetic, or lab-grown

Real emerald, chemically and optically — beryl colored by chromium — but grown in a laboratory over weeks. Perfectly legal and legitimate to sell, and in fact often cleaner and more uniformly colored than a natural stone. It is a fraction of the price. The only problem is when it is sold without saying so.

Imitation

Not emerald at all: green glass, doublets glued from two materials, or other green stones sold under a confusing name. Much cheaper again.

What you can observe yourself

• Inclusions that look organic. Natural stones have irregular, three-dimensional internal features. Glass typically has round gas bubbles. A ten-power loupe and patience will show you the difference more often than not.
• Uniformity that is too good. A large, flawless, perfectly even stone at a friendly price is the clearest warning sign there is.
• The seam of a doublet. Viewed from the side, a glued stone often shows a flat plane where the two halves meet.

Myths that do not work

Scratching the stone, breathing on it to see how fast it clears, testing it with water, judging it by weight in the hand, or checking whether it is cold to the touch. None of these separate a natural emerald from a well-made synthetic, and some of them damage the stone.

What actually settles it

A gemological laboratory. The instruments look at growth patterns, inclusion types and trace elements, and that is the only reliable answer. For a significant purchase, a laboratory report is worth its cost, and any store should be comfortable with you obtaining one.

Short of that, what protects you is a written certificate that names the species explicitly, from a seller who will still be there next year.