Phenomenal gems

Phenomenal gems

There are some stones that interact with light in ways that produce unusual optical effects (phenomena). Some of those phenomena belongs to specific gems, and sometime other gems may, or may not, show some other effects, depending of their quality and variety.

Phenomena are divided in 8 groups:

chrysoberyl

1. CHATOYANCY; consist of bands of light  reflecting from needle-like inclusion, parallel. If cutted properly, the stone will reflect the light creating a shiny line that looks like a cat’s eye. The best type of cut to enhance the phenomena is a “cabochon” that concentrates the eye across the dome of the cabochon. The top quality gems shows an eye sharp and intense. The most valuated chatoyant gem is the cat’s eye chrysoberyl that, in addition to chatoyancy, show another optical effect called “milk and honey”: it’s a 2 tone effect  seen when a chatoyant  gem is at right angles to a light source. One side turns milky and the other a dark honey color. In an other gem, a “tiger eye quartz”, the phenomena is shown even without a direct light, or a faceted cut.

star sapphire

2. ASTERISM; the effect results from crossed chatoyant bands. 
The light reflects from tiny needle-like inclusions oriented in different directions. Usually, if a stone shows this kind of inclusions, the cutter prefer the cabochon shape to enhance the phenomena, otherwise the gem will look just translucent. Actually, if the stone shows a sharp nice star, it will increase its value. Star sapphire and star rubies are the most valued gems that displays asterism.

       

3.   AVENTURESCENCE; is a glitter effect   made by some flat inclusions inside the stones. In natural gems this phenomena is typical of  a variety of quartz called “Aventurine”, but is very common  in low cost goldstones, that are just glass or plastic with filled with glitter.

opal

 4. PLAY-OF-COLOR; the Opal shows this phenomena. Opal is not a Chrystal,  is made of microscopic spheres that breaks up the light into spectral colors depending of the size of the      spheres and from the way they interact with light, the stone will show different body color and different pattern of phenomena. Usually in the trade is preferred a dark body color where the effect is more visible. The most valuated is the “fire opal”, red gem that may or may not shows play-of-color.

moonstone

5. ADULARESCENCE; phenomena typical of the moonstone. The effect is shown like a light blue clouds that appears when the light hits the gem. It’s hard to see the phenomena in a rough stone, the cutter usually polish the stone in a cabochon to enhance the effect.

Labradorite

6. LABRADORESCENCE; is the Labradorite's  phenomena; is a flash of color that appear when light strikes the stone from specific angles. The cutter always try to cut the stone while the effect is more visible from the front.

mother-of-pearl

 7. IRIDESCENCE; in nature we call iridescence the rainbow color that we see when a light bean is broke in a spectral colors. On jewels we can see this effect on different stones, for example Ammonite, fire Agate and also on Pearls and Mother-of-Pearls where, in this case, the phenomena is called ORIENT.

fire agate

alexandrite chrysoberyl

8. COLOR CHANGE; it’s a very rare phenomena that shows a effective change in color of a gem from daylight to incandescent light. The most well-known and valuated color change gem is Alexandrite Chrysoberyl, that in its best quality turn from vibrant green to rich red. Emerald by day and Ruby by night. Some other stones can show this effect: Sapphire, Garnet, Spinel.