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

Updated: 6 days ago

We are long past the assumption that a diamond will be of natural origin. Following the surge in retail sales will be a wave of laboratory-grown diamonds on to the second-hand market. As natural 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! Check out this introductory guide to separating natural and laboratory-grown diamonds from observation alone.

Natural 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. High-quality stones are more difficult to separate as we can only visually distinguish natural and laboratory-grown diamonds if features physically exist in the stone. As luck would have it, the chances are in often in our favour. Let’s have a look at my top 3 features that can determine us to determine a natural diamond versus a laboratory-grown diamond.

1. Features only seen in natural 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 (that’s right - a diamond within a diamond!). Other exclusive inclusions include garnet, diopside, hydrogen clouds and, more rarely, sapphire and kyanite. Spot one of these and the diamond is definitely natural.

Read more about lab-grown diamonds:

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

2. Features only seen in HPHT laboratory-grown diamond

Metallic flux inclusions in HPHT synthetic diamond ©The Gem Academy

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 it is angular, rod-like, ash-like (dendritic) or appears as random paint-splashes.

Metallic flux is dark grey in colour, opaque, and has a metallic lustre - which sometimes shows iridescence. 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 only recently in 2016 by GIA geologist Dr Evan Smith and his team.

There are also some unique colour tints found in "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.

Want to learn all about lab-grown diamonds?

Check out: The ultimate online course on laboratory-grown diamonds

3. Features only seen in CVD laboratory-grown diamonds

Hazy graining in CVD synthetic diamond ©IGI

Many report that there are no distinguishable features within CVD diamonds. Although it is less likely to be any characteristic features for CVD origin, there are a few possible tell-tale signs. One feature is heavy parallel graining throughout the stone due to a high amount of internal strain due to the layered growth of CVD synthesis. This graining is often intense and gives the CVD diamonds a “hazy” appearance. This is similar to the appearance of HPHT-treated natural diamonds - however, either one must be identified and disclosed as there are implications on price compared with a natural diamond. An exclusive feature for CVD laboratory-grown diamonds is graphite inclusions that are within just one plane of the stone, which can occur if they were trapped within the same growth layer during synthesis.

What if none of these features exist?

An obvious thing to look for is laser inscriptions on the stone. If these don't exist..., well - this is when it gets a bit harder.

Tests are needed when no visual features are seen. These range from simple tests such as UV testing and a polariscope... to more advanced spectroscopy testing. If you are well trained... its surprised how far just observation, UV and a polariscope will take you. As a rough idea... it should help you identify most natural and HPHT laboratory-grown diamonds. CVD are certainly much tricker as they are less likely to have a UV response and the strain patterns seen with a polariscope can be confusing.

To learn more about laboratory-grown diamonds and how to separate them from natural diamonds (and vice-versa), check out my online course of laboratory-grown diamonds. This course discusses all of the testing techniques available with video explanations and comprehensive test results.

Want to learn all about lab-grown diamonds?

Check out: The ultimate online course on laboratory-grown diamonds

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