Home Top 10 Gemstones Special Effects

Top 10 Gemstones Special Effects

Gemstones are more than shiny, colored stones-some of them also have certain optical "special effects." These special effects, which are natural in the mineral, are called "phenomena" by gemologists. Skillful gem cutting and techniques of the jewelry designer can bring out these special effects to their fullest, when attractive, or hide them when unattractive.

Most of these special effects are:

	1. Fire The special effect called fire by diamond cutters is due to distribution, the ability of the stone to draw light apart into its constituent colors. This task is just like the glass prism that unfolds sunlight into the rainbow by refraction. The fire of a diamond refers to the bloom of its bright highlights. Of the major gemstone minerals, only diamond and zircon have physically powerful enough refractive properties to produce distinct fire, but other stones such as benitoite and sphalerite show it too.
	2. Schiller Schiller is also known as play of color, in which the internal of a stone displays flickers of color as it is moved in the light. Opal is particularly valued for this trait. There is no real object inside the stone. This special effect arises from light interfering within the microstructure of the mineral.
	3. Fluorescence Fluorescence is the ability of a mineral to turn arriving light of ultraviolet color into light of a visible color. The special effect is well-known if you've ever played in the dark with a blacklight. Many diamonds have a blue fluorescence that can create a pale yellow stone look whiter, which is desirable. Some Southeast Asian rubies (corundum) fluoresce red, giving their color an extra bright redness and accounting for the high price of the best Burmese stones.
	4. Labradorescence Labradorite has become a popular stone because of this special effect, a remarkable flash of blue and golden color as the stone is moved in the light. It arises from light interference within microscopically slim layers of twinned crystals. The sizes and orientations of these twin lamellae are consistent in this feldspar mineral, thus the colors are limited and powerfully directional.
	5. Change of color Certain tourmalines and the gemstone alexandrite attract certain wavelengths of light so strongly that in sunlight and indoor light they appear different colors. Change of color is not the same as the changes in color with crystal course that affects tourmaline and iolite, which are due to the optical property called pleochroism.
	6. Iridescence Iridescence refers to all sorts of rainbow effects, and in fact schiller and labradorescence can be measured as varieties of iridescence. It is most well-known in mother-of-pearl, but it is also found in fire agate and some obsidian as well as many artificial gems and jewelry. Iridescence arises from the self-interference of light in microscopically slim layers of material. A famous example occurs in a mineral that's not a gemstone: bornite.
	7. Opalescence Opalescence is also called adularescence and milkiness in other natural resources. The cause is the same in all: subtle iridescence caused by spreading of light within the stone by thin microcrystalline layers. It can be a white haziness or spongy colorations. Opal, moonstone (adularia), agate and milky quartz are the gemstones most excellent known for this special effect.
	8. Aventurescence Inclusions in a gemstone are frequently considered flaws. But in the right kind and size, inclusions create interior sparkles, particularly in quartz (aventurine) where the special effect is called aventurescence. Thousands of tiny flakes of mica or hematite can turn plain quartz into a sparkling rarity or feldspar into sunstone.
	9. Chatoyancy When contaminated minerals occur in fibers, they give gemstones a silky appearance. When the fibers line up along one of the crystalline axes, a stone can be cut to display a brilliant reflective line-a special effect called cat's-eye. The most common cat'seye gemstone is quartz, with traces of the tough mineral crocidolite. The version in chrysoberyl is the most precious, and is called just cat'seye.
	10. Asterism When tough inclusions align on all of the crystal axes, the cat'seye effect can appear in two or three directions at once. Such a stone, cut accurately in a high dome, displays the special effect called asterism. Star sapphire (corundum) is the best-known gemstone with asterism, but other minerals rarely show it too.