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Jewelry Articles | | ABOUT AMETHYST & CITRINE QUARTZ |
Amethyst is often called the “royal purple” gemstone, and the beautiful rich color of amethyst quartz has made it a popular gem for jewelry. The more desirable colors of this variety of quartz result from a saturation of purple or violet. These colors may sometimes lean toward blue (accentuated by fluorescent light or daylight) and at other times toward red (enhanced by incandescent light).
While most people favor darker, deep purples with flashes of red in incandescent light, a definite market also exists for the paler, pastel-lavender hues. Lighter material tends to sell for several dollars less per carat and makes an attractive gemstone if well-cut.
Size often isn’t an important factor for amethyst. Rough material in a wide range of sizes is readily available.
Citrine, a close relative of amethyst, has a far different color. People tend to look for bright, pure yellow citrine, though it can range from very pale yellow to deep orange.
Because of its visual similarity to topaz, citrine often has been called “topaz quartz” or “madeira topaz,” but you should avoid these terms. Obviously, precious topaz is an entirely different species of gemstone.
Citrine yellows can occur naturally in quartz, but more often result from the heat treatment of amethyst. Atomic iron impurities in the quartz produce the yellow.
Another variety of quartz — ametrine — combines amethyst and citrine in one gemstone. For many years,
people believed this bicolor stone resulted from treatment. But it recently was proven to be a completely natural gemstone produced in only one known location — southeastern Bolivia, toward the border with Brazil. Ametrine is growing in popularity because of its beauty, availability and size range. It’s popular with gem carvers because it comes in larger sizes and is very clean optically.
Today, natural and synthetic amethysts are used in the jewelry industry. Natural and synthetic amethyst look very much alike, though synthetic material tends to be very regular and repeatable in color. The color of synthetic materials tends to be quite rich and deep; natural amethyst can have deep color too, of course, but these fine stones are rarer.
Gemologists have identified a few ways to distinguish synthetics from naturals, especially by microscope:
- Inclusions — Synthetic amethyst often has tiny inclusions known as “breadcrumbs.” In natural amethyst, included crystals of another mineral such as goethite, hematite and lepidocrocite are often visible. Natural amethyst also may have a series of irregular parallel stripes known as “zebra-stripes.”
- Twinning — Amethyst may show so-called Brazil-law twinning, a growth feature that appears as a series of parallel triangular lines that help to define color zoning. This feature can be seen when looking down the crystal axis of the gem.
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| GEMSTONES, RADIOACTIVITY & TESTING |
Many varieties of colored gemstones owe their color to the effects of radiation exposure.
Some receive a natural radiation dose before they are ever mined, while others are exposed
to radiation in a laboratory.
Examples include blue and green topaz, pink to purplish red tourmaline, golden beryl, red zircon,
some yellow to orange sapphires, amethyst and smoky quartz. The colors achieved by laboratory
irradiation treatment often duplicate and may be more pronounced than those found in nature.
Finding that gemstone jewelry has “natural” or “treated” gems can influence its value. But testing
an irradiated gemstone for radioactivity also is now a matter of concern.
Sometimes the gems themselves are radioactive because they contain radioactive elements.
These “radionuclides,” as they are called, may be naturally occuring trace elements such as
uranium or thorium and their radioactive decay products, or they may result from contamination.
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Gemstone and Birthstone Information |
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