Cat's-eyes and star-stones are popular names for the special effects caused by light reflections in certain gemstones. They can usually only be seen when the gemstone is cut in a rounded or domed shape (cabochon). The reflections that cause cat's-eyes and star-stones are one way in which color is displayed in gemstones.
Color in gemstones, as it does in all other substances, starts with light. Visible light, the light that humans see with the naked eye, is only a small part of the total light available. Visible light is also called "white light," because it looks white to us. All light consists of wavelengths of individual colors. Visible light is a combination of color wavelengths that blend to form white. You can easily see all the colors in white light when moisture in the air separates sunlight into a rainbow after a rain.
All solids, including gemstones, separate the colors in light. Nearly all substances absorb some color wavelengths. The colors that they do not absorb are reflected back. Those reflections are the colors that we see. Each gemstone will absorb or reflect different color wavelengths depending primarily on the chemicals it contains. For example, peridot absorbs all but the green color wavelengths. The green is reflected back, making peridot look green to us. Rubies absorb everything except red and some blue wavelengths. The red and unabsorbed blue are reflected back to us as a deep red color. Gemstones appear black when they absorb all color. Some gemstones in their chemically pure state don't absorb any color wavelengths. Beryl is one example. Because all the colors are reflected back, the gemstone is the same color as the light striking it. That makes it appear colorless to us. However, tiny amounts of impurities in a stone can cause some light to be absorbed rather than reflected. Depending on the impurity in beryl, we see green (emerald), blue (aquamarine), yellow (heliodor or golden beryl), or pink (morganite).
While impurities can change the color of the whole
Go To Page: 1 2
