GIA Gemology Guide: Feather Inclusions in Diamonds

For a GIA student or professional jewelry appraiser, identifying and evaluating internal characteristics is fundamental to diamond grading. A feather is one of the most common—and occasionally most concerning—inclusions found in a diamond. While often benign, its location and size can significantly impact both a diamond's visual performance and its physical durability.

1. What is a Feather?

"Feather" is the general trade term used by the GIA to describe any break, fracture, or cleavage within a diamond. When viewed under magnification from the right angle, these breaks often take on a wispy, whitish, and feathery appearance—hence the name.

How do they form?

Feathers can be either natural or man-made:

Natural: Most feathers are natural fractures that occurred deep within the earth due to the immense heat, pressure, and geological stress the diamond underwent during formation or its violent journey to the earth's surface.
Man-Made: Feathers can also be created or worsened during the cutting and polishing process, or through accidental impacts (wear and tear) after the diamond has been mounted.

2. How to Plot a Feather (GIA Standards)

Feathers can be entirely internal, or they can breach the surface of the diamond. Under GIA standards, a feather is always classified as an inclusion (an internal characteristic).

Plotting Steps:

Locate the Feature: Using a microscope or a 10x loupe, examine the break from multiple angles. Feathers can appear transparent and nearly invisible from one angle, but bright white or reflective from another.
Plotting in Red Ink: Because feathers are considered inclusions, they are plotted exclusively in red ink, regardless of whether they are entirely internal or breach the surface of the stone. Draw the exact shape of the feather as you see it using a red line.
Do Not Fill: Feathers are drawn as lines or enclosed shapes denoting the extent of the fracture. Do not color or fill them in.
Key to Symbols: "Feather" is listed in the Key to Symbols. If the feather is the grade-setting characteristic, it will be listed first.

3. Feather vs. Similar Characteristics

A skilled grader must distinguish a standard feather from other inclusion types that involve fractures or breaks:

Feather vs. Cleavage: In general gemology, a "cleavage" is a break along a distinct atomic plane, while a "fracture" is a break in any other direction. However, for GIA plotting and grading purposes, both cleavages and fractures are simply grouped together and plotted as "Feathers."
Feather vs. Bruise: A bruise is a tiny area of impact (usually on a facet junction) accompanied by minute, root-like feathers radiating inward. It is plotted differently—specifically using a red X without any green—rather than drawn as a standard feather shape.
Feather vs. Cavity: A cavity is an angular opening on the surface, sometimes created when a surface-reaching feather breaks away during polishing. If a wide, jagged opening is present, it is a cavity (plotted with both red and green ink); if it is just a hairline crack breaking the surface, it remains a feather (plotted in red only).

4. Evaluation and Appraisal Considerations

For appraisers and gemologists evaluating diamonds—especially for estate or insurance purposes—feathers require careful analysis because they are one of the few inclusions that can present a legitimate durability risk.

Durability and Placement: The most critical factor when evaluating a feather is its location.

Low Risk: A small feather safely enclosed deep within the center of the diamond generally poses no structural risk.
High Risk: A large feather that reaches the surface near the girdle or at a vulnerable point (such as the sharp corner of a princess cut or pear shape) is a major durability hazard. A hard blow to this area could cause the diamond to chip or the fracture to spread. Appraisers must note these high-risk feathers, as they severely impact the stone's replacement value and may necessitate special care during setting.

Impact on Clarity Grade: A tiny, completely internal hairline feather may keep a diamond in the VVS or VS range. However, a large, highly reflective feather that crosses the table or a surface-reaching feather on the girdle will quickly drop the grade into the SI or I categories.

Visual Impact: Large feathers can impede the path of light through the diamond. Instead of bouncing back to the viewer's eye as brilliance, light may hit a large feather and leak out the sides of the stone, creating dull or dead spots in the diamond's face-up appearance.

Summary for GIA Students

Definition: A break or fracture within the diamond that often looks whitish or feathery.
Plotting: Plotted using red lines only, regardless of whether the break is entirely internal or surface-reaching.
Key Factors: Pay close attention to the size and location of the feather. Feathers located near the girdle or sharp corners, especially if they are surface-reaching, present significant durability risks that must be accounted for in grading and appraisal.