Professional Jeweler Archive: Spinel Galaxy

March 2000

Gemstones & Pearls/Gemology


Spinel Galaxy

First in a series on inclusions in natural and synthetic gemstones


Studying inclusions in colored gemstones is like voyaging under the sea or into outer space. Are those tiny specks heavenly asteroids. Is that elaborate design a coral reef? Whatever an inclusion suggests, it’s fun and worthwhile to take the time to examine it.

Analysis of inclusions is a main component of gemology, allowing you to study the internal structure of gemstones and helping you to distinguish among similar-looking species and varieties. Jewelers and gemologists often analyze inclusions to determine whether a gemstone is natural or laboratory-grown. In fact, the use of microscopy in gemology grew out of a need to examine gems after the advent of ruby synthesis in the late 1800s.

“Through the microscope, the story unfolds as the kaleidoscopic world of gemstone inclusions comes to life,” say Edward J. Gübelin and John I. Koivula in their Photoatlas of Inclusions in Gemstones (ABC Edition, Zurich, Switzerland, 1986). “Solid crystal inclusions glowing under polarized light blink and change color as their host is turned in the field of view ... The gemologist of the future will be greatly dependent on a very strong knowledge of inclusions.”

– by Robert Weldon, G.G.

Discoid Stress Fracture

At 30X the discoid tension fracture shown in the center of this photograph of a red Sri Lankan spinel does its best to imitate an interstellar galaxy. At the center of the fracture is a relatively large octahedral inclusion of unknown identity. Its presence caused the stress fracture as the gem grew.

Hovering just above the fracture like a small orbiting planet, a small octahedral inclusion casts its reflection in the shiny surface of the fracture. A series of other minute octahedral inclusion strings can be seen below the fracture – affirming the identity of the stone as natural red spinel.


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