Professional Jeweler Archive: Feathers and Cleavage

May 2001


Feathers and Cleavage

The sexy side of those minuscule fissures in a diamond

Because gemology is such a curious blend of science, beauty and business, the nomenclature blends poetry and science. A common word such as “crack” becomes “fissure.” An even more alluring term for it is “feather.” So the phrase “Your rock has a crack in it” effectively becomes “Your diamond has a beautiful little feather inside.” Both statements are scientifically accurate; the latter is more appealing to use with customers.

Whatever you call them, they’re cracks, even if they are microscopic. You may be relieved to know feathers are present in many of today’s finest diamonds, and in the vast majority of cases, they don’t jeopardize the longevity or beauty of the gem.

Where Feathers Come From

Feathers in diamond occur for any number of reasons, not the least of which is the arduous journey the stone takes on its geothermal path up a volcanic pipe toward the earth’s surface. Later, mining also involves rather violent processes (including dynamite) that are believed to cause some feathers to fly.

Natural erosion of kimberlite pipes and subsequent river journeys may tumble a diamond along a riverbed, often for hundreds or thousands of miles. But diamonds found in alluvial deposits, such as along Namibia’s coastline, are often feather-free. What seems like an anomaly actually makes sense: Tumbling and knocking a diamond along the river bottoms often causes existing feathers to grow. Then the diamond cleaves, and two smaller, feather-free diamonds resume their trip.

Visible Cleavage

Feathers in a diamond are visible forms of cleavage. They form along planes of atomic weakness in the diamond’s structure. Sometimes feathers appear alongside crystals of another mineral included in a diamond because of the spatial tension these crystals create. During the cutting process, minuscule feathers running from the girdle into the diamond often form as well. These tiny feathers are referred to as “bearded girdles.”

But Almost Invisible

Because they’re so small, feathers are often almost invisible, particularly when the cleavage runs parallel to the viewer’s vision, so it’s advisable for anyone looking for feathers in a microscope to tilt and swivel the diamond, viewing it from all angles.

When cleavage is viewed at a right angle, with illumination that lights up the surface of the feather, the inclusion is much more striking. Some feathers occur only internally, while others reach the surface of the diamond. Surface-reaching fissures are sometimes enhanced with a proprietary substance that masks the appearance of the feather.

Durability in Question

A few large feathers can leave the durability of a diamond in question, particularly in cases where a well-placed blow could finish the cleaving process.

But internal feathers that are small, unobtrusive and have no possibility of enlarging or harming a diamond can also be viewed as marks that distinguish it from all others. No two feathers are alike. Nor are two cleavages.

– by Robert Weldon, G.G.

Locate the two small included feathers in this diamond. In one of the feathers, illuminated with oblique, diffused lighting, you can see a step-like cleavage plane which is characteristic of diamond. Microphotograph at 35X.

Photo by Robert Weldon.

Copyright © 2001 by Bond Communications