Flawed But Beautiful: Why Gemologists Love Diamond Inclusions

December 19, 2017  |  Joyce Kauf  |  SPONSORED BY: Diamond Producers Association

Inclusions are a natural diamond’s signature. Alethea Inns, director of gemology and education at the American Gem Society (AGS), explains the fascinating facts of this phenomenon.

Alethea Inns, Director of Gemology and Education, American Gem Society.

What are inclusions?

In the world of gemology, inclusions are defined as internal visible features in either a rough crystal or faceted gemstone. Inclusions are important in gemology because they can tell trained gemologists whether the gemstone is natural, synthetic, or treated, or even where it came from.

Inclusions are often referred to as “flaws,” or “imperfections,” but in reality, they are part of the natural geological process and an essential and fascinating part of gemology. Inclusions make each diamond unique, as no two diamonds are identical, and are even used by gemological laboratories to verify a diamond’s identity. A diamond with natural inclusions is like a snowflake.

An orange heart-shaped crystal on a diamond’s table (American Gem Society).

Inclusions can consist of other mineral crystals that look like what they are called — for example, a break in the crystal lattice is called a feather because it can resemble the texture of a feather. A pinpoint inclusion is just that — it looks like a pinpoint — while thin, elongated inclusions are called needles.

How do a diamond’s imperfections enhance it as something unique and authentic?

Inclusions are often used to determine the relative value of a diamond, based on their size, nature, number, position in the diamond, and relief — or visibility — but they are also so much more. Inclusions tell us the story of the diamond — how it formed, what it went through in the earth, and how it got to the surface of the earth.

In fact, for geologists and researchers, the most prized diamonds are those specimens with large, visible inclusions. Some geologists spend their entire careers studying one type of diamond inclusion and its implications. This is because diamonds act as vessels that can capture minerals from the mantle of the earth and can give us information about the growth environment, and even the age of our planet.

A purple-pink crystal, seen through the pavilion’s facets (American Gem Society).

The oldest diamonds have been dated at up to 3.5 billion years old — which is not something you can say about a laboratory-grown diamond.

How are they formed? What conditions in the earth need to be present?

Conditions have to be just right not only to form diamonds, but to form the inclusions that occur within them. Diamonds are generally theorized to have formed at depths greater than 150 kilometers, at pressures of around 5 GPa (gigapascals) and at 1,000 degrees Celsius, and need a specific chemistry in order to grow.

This is why they are geologically rare. Diamonds are carried to the earth’s surface by magma — molten and semi-molten rock found beneath the earth’s surface — younger than the host rocks in which they were formed. These two rock types in which diamonds grow in the mantle are eclogite and peridotite, and occur at different depths in the earth.

A feather on a pavilion (American Gem Society).

Diamonds are carried to the earth’s surface in one of only three rare types of magma. The most important type of magma is known as kimberlite, such as the Diavik mine in Canada.

The Argyle mine in Australia, famous for its pink diamonds, is derived from a rarer type of magma, called lamproite, with an entirely different geochemistry. Pink diamonds from Argyle often have coesite inclusions, which are high-relief transparent crystals.

How do inclusions manifest themselves in diamonds?

Most diamond inclusions are classified as syngenetic, which means the inclusion forms at the same time as its host. Pyrope garnet is an example of a syngenetic inclusion you may find in a diamond, and is usually a dark-reddish included crystal.

Furthermore, diamonds are classified into different types based on the amount of nitrogen that aggregates in the crystal lattice. Some diamond types can be categorized by inclusion types, such as Ib diamonds with clusters of dark “Ib needles.” Large cape diamonds with N2 and N3 aggregates often have high-relief transparent garnet crystals and fine, transparent linear growth, known as “transparent graining.”

While there are still many unanswered questions about how exactly diamonds form, their inclusions are a window into the history of the earth, and their journey to the surface. They are an opportunity to carry a piece of that history with you, so you can admire diamonds from the inside out.

All part of the story

“Inclusions are just one part of the much bigger story of selling a diamond,” says Erik Runyan, owner of Erik Runyan Jewelers in Vancouver, Washington. “My experience shows that people aren’t afraid of inclusions, but rather, their concern is how they affect the beauty of the diamond.

As jewelers, we have to convey that inclusions are natural phenomena occurring in the creation of these unique and rare stones.”

Runyan notes that the diamond-purchasing public is becoming more knowledgeable. “In the past, customers had some idea of the 4Cs, but now they are familiar with the entire GIA grading scale. It is amazing that customers will ask for SI1 — except they don’t know what that means in real life. And that is why it is critical that the selling conversation transitions from looking at diamonds on paper to seeing and holding them in person,” he advises.

He prefers to sit down with the customer and let her select the diamond that she finds the most beautiful — without considering specific criteria such as clarity or color.

“After the emotional connection is made is when I start talking about the quality characteristics that drew her to that diamond,” he says.

Runyan also talks about the origins of the diamond, emphasizing the “incredible journey” each of these rare stones has made over billions of years.

Only a handful of his customers have specifically requested synthetic diamonds, produced either through High Pressure-High Temperature (HPHT) or chemical vapor deposition (CVD) methods. And even in those cases, he says, “my impression is that these customers are not looking for a stone without any imperfections. They are interested in synthetic diamonds because of their low-carbon-footprint and/or no-conflict associations.”

Diamond jewelry. Erik Runyan jewelers.
Diamond jewelry. Erik Runyan Jewelers.

While synthetic diamonds exhibit the same chemical, physical and optical properties as natural diamonds, there is an important element that cannot be replicated in a laboratory.

“There are two reasons people buy a diamond,” he says. “The first is that diamonds are simply beautiful. And secondly, they are rare. It is unusual for someone to own something so unique that comes from the earth. A diamond is given as a symbol of love. But a lab-grown diamond does not evoke any romance at all.”

Main image: Diamond jewelry. (De Beers; Erik Runyan Jewelers)


Flawed But Beautiful: Why Gemologists Love Diamond Inclusions

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