Diamond Inclusions Explained: Feathers, Clouds, Crystals

An inclusion is a feature inside a diamond, formed as the stone grew deep in the earth or as it was cut. They are the reason clarity grades exist, and they are one of the things that make each natural diamond individual.

Why inclusions exist

Natural diamonds form under intense heat and pressure over a very long time. Tiny crystals of other minerals can be trapped during growth, and the stone's structure can show small fractures or growth lines. These are not signs of poor quality in themselves. They are the stone's history.

The main types

• Crystals: small mineral grains trapped inside the diamond, which can be colourless, dark or coloured.
• Feathers: small fractures that look like tiny cracks or feathers, usually within the stone.
• Clouds: groups of tiny pinpoints that can look like a hazy patch.
• Pinpoints: very small dots, sometimes alone, sometimes in groups.
• Needles: thin, rod-shaped crystals.
• Twinning wisps and growth lines: features of the stone's internal structure.
• Knaits and naturals: surface features. A natural is a small bit of the original rough surface left on the stone.

How they appear on a report

Clarity is shown as a grade, and the report may include a plot: a diagram of the stone that marks the position and type of notable features with symbols. Red marks generally show internal features and green marks show surface features. See how to read a diamond certificate step by step.

Which ones matter?

For appearance, what matters is whether an inclusion can be seen without magnification and how it affects light.

• Dark crystals under the table are more visible than pale ones near the edge.
• Clouds in large numbers can make a stone look hazy.
• Feathers reaching the surface can be a durability concern if they are near the girdle or the edge.

Most inclusions at VS clarity and above, and many at SI, are invisible at normal distance. See diamond clarity: VS, SI and VVS.

Do they affect strength?

A few can. Feathers that reach the surface and are near the edge can be points where a stone chips if it is hit. Ask about them for a ring you will wear daily. See are diamonds unbreakable?.

Inclusions as identification

Because inclusions are unique, they are like a fingerprint. A jeweller or laboratory can recognise a stone by its pattern of features. This is one reason a plotted diagram helps verify that a stone matches its certificate.

Treatments

Some diamonds are treated to reduce the visibility of inclusions, for example by laser drilling or by filling fractures. Treated stones must be disclosed and are priced lower. A proper laboratory report will say if a stone is treated.

Choosing with inclusions in mind

1. Look at the stone through a loupe with the jeweller.
2. Find where the main feature lies, and think about how the setting covers it.
3. Prefer a stone that is eye-clean over one with a higher grade you cannot see.

Next step

Book an appointment to see a few stones under magnification and compare their plots, or browse our diamond earrings, where the small stones are chosen for a clean, bright appearance.