How to tell if a diamond is natural or laboratory-grown (just by looking!)

By Julia Griffith FGA DGA EG

As diamonds and laboratory-grown diamonds promise different ideologies and have increasingly different values, the integrity of both industries rely on the correct separation and disclosure of these two products. Luckily, The Gem Academy is here to help! Here's an introductory guide to separating natural and laboratory-grown diamonds from observation alone....

Diamonds and laboratory-grown diamonds are the same material so there’s no way to tell them apart just by looking at them, right? Wrong. Features specific to their different growth origins allow a trained gemmologist to determine whether a diamond is natural or laboratory-grown.

Granted, not all laboratory-grown diamonds can be identified just by looking at them. High-quality stones are more difficult as we can only visually distinguish diamonds and laboratory-grown diamonds if features physically exist in the stone itself.

Let’s have a look at my top 3 features that can help us to determine a diamond versus a laboratory-grown diamond.

All gems can trap pieces of their surrounding environment as they grow. These are known as inclusions and give us a snapshot of the stones growth environment.

Natural diamonds grew in the mantle of the earth and, as a result, can contain mineral inclusions that are never found in laboratory-grown diamonds.

A common inclusion found in natural diamond is a diamond crystal (that’s right - a diamond within a diamond!). Other exclusive inclusions include garnet, diopside, hydrogen clouds and, more rarely, sapphire and kyanite. Spot a transparent crystal that is either colourless or coloured then the diamond is natural.

Read more about lab-grown diamonds:

Laboratory-grown diamonds 101: An introductory guide to what, why and "how much?

HPHT laboratory grown diamonds grow within a metallic flux of nickel, iron and cobalt. As a result, a common feature of HPHT laboratory-grown diamonds is metallic flux.

This metallic flux can appear in a few forms. Most commonly they appear angular, rod-like, or ash-like (dendritic).

Metallic flux is dark grey in colour, opaque, and has a metallic lustre that sometimes shows iridescence. Metallic flux is evidence that the stone is a HPHT laboratory-grown diamond*.

There are also some unique colour tints found in near-colourless HPHT laboratory-grown diamonds including pale blue, known as a blue-nuance, as well as pale green. Read more about these blue-nuanced stones here.

*Metallic inclusions can exist in natural diamonds but are only seen very rarely. These are, again, made from iron and nickel and their existence has revealed a new origin for diamonds below the mantle of the Earth within the transition zone. These diamonds are rare Type II diamonds. This was first recorded recently in 2016 by GIA geologist Dr Evan Smith and his team.

Want to learn all about lab-grown diamonds?

Many report that there are no distinguishable features within CVD laboratory-grown diamonds. Although it is less likely to be any characteristic features in these stones, there are a few possible tell-tale signs.

An exclusive feature for CVD laboratory-grown diamonds are graphite inclusions that lay within a single two-dimensional plane. This occurs when there is a pause in growth and graphite builds up on the surface layer of the crystal before the crystal continues to form - This trapping a layer of graphite.

One feature is heavy parallel graining throughout the stone due to a high amount of internal strain, which is a common characteristic for LGDs produced by the CVD synthesis method.

This graining can be intense and gives the CVD diamonds a 'hazy' appearance. This is similar to the appearance of heavily grained natural diamonds (and those with HPHT-treatments). This feature is therefore typical - but no conclusive evidence that can lead to identification.

An obvious thing to look for is laser inscriptions on the stone. If the stone has no laser inscription AND no observational features - this is when identification gets a bit harder.

Tests are needed when no visual features are seen. These range from simple tests such as using a screener, to more advanced spectroscopy testing.

To learn more about laboratory-grown diamonds and how to separate them from natural diamonds (and vice-versa), why not come to my practical workshop?

I'll show you my 7-step guide to identification, and you'll have access to over 50 laboratory-grown diamonds to see and test for yourself.

Check out my online course of laboratory-grown diamonds This course discusses all of the testing techniques available with video explanations and comprehensive lists of possible test results.