Gem Focus – November 2019

Posted on November 6, 2019 by The Gemworld Staff

Topaz:
A gem with several colors and identities.

There are two suggestions for where the name topaz originated from; one is “topazios” in Greek referring to the island, also known as Zabargad, and the other is “tapaz” in Sanskrit translates as fire. Although Zabargad Island in today’s Egypt is the source of ancient peridot, it doesn’t produce any topaz. Most scholars agree that it was a mistake in identification. Regardless of its origin, topaz has been around as a revered gem in several colors for millennia. Today, most consumers think of topaz as an affordable blue stone, or even poor man’s aquamarine, while gem connoisseurs appreciate other colors especially pink and yellow.

Topaz is an aluminum fluoro-hydroxyl-silicate and forms in the orthorhombic crystal system. Its perfect basal cleavage is challenging for cutting, yet its hardness of 8 makes this gem durable. The most common variety is colorless but a range of blue, yellow, pink, purple, and red are known. Since it is an allochromatic gem, all the colors are caused by trace elements such as chromium for pink and red, or imperfections in the crystal system leading to blue, yellow, and brown. Topaz is a highly pleochroic gem, the best examples display eye visible pleochroism. Undoubtedly the rarest of all topaz colors is the red category. The term imperial came from the discovery of pink topaz in Russia during the 19th century. Initially, only the Czar and his family could own the stones, hence the term imperial. It then became a generic term for all yellow to pink topaz until dealers confined it to a range of rich, saturated colors. The GemGuide has always reserved the term imperial for stones that show the reddish or purplish red overtones. Our price charts differentiate yellow vs. imperial topaz. Also, gem professionals must pay attention to the possible heat treatment of pink topaz while identifying.

Yellow topaz has many shades of yellow from light tones to warmer hues, sometimes with more brown than desired. Once brown tones are dominant, it may be called sherry topaz. Unfortunately, there is a tendency of calling smoky quartz or dark citrine as smoky topaz but this confusion in public shouldn’t fail practicing gemologists when proper identification
is performed.

Natural blue topaz exists, yet almost all fashioned blue topaz in the gem trade is treated color. There are three “shades” of blue topaz, sold as London, Swiss and Sky blue, respectively from darker to lighter tones. Irradiation followed by heat treatment would create blue colors in otherwise colorless topaz. The other irradiated topaz color is green, although not commonly seen anymore.

The other common treatment of topaz is coating. Although the bright iridescence coating of topaz is easily detectable, non-iridescent color coating on colorless topaz is a well-known practice. Lack of pleochroism in these samples is a very good indication of such treatment.

Topaz comes from many different localities in the world. Brazil, USA, Pakistan, Russia, Ukraine, Burma, Nigeria, Namibia, and Zimbabwe are the noteworthy localities, although there are more smaller productions in other countries.

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