Topaz



Topaz makes an ideal gem. Good hardness and desirable colors, combined with a relative abundance and availability make it one the most popular gemstones. the most valuable colors of Topaz are the golden orange-yellow type, called Imperial Topaz, and the dark pinkish-red and orange-red colors.

 The value increases with a deepness of color in orange and reddish hues. The most commonly used colors of Topaz in jewelry are the blue types. It was not until this past century that blue Topaz became widespread on the gem market since virtually all blue gem Topaz is irradiated and heat treated.

Where do Do you find the Topaz stone?

Topaz obtains much of its popularity from its beautiful colors and its status as a birthstone. Natural topaz colors include rare and valuable yellow, orange, pink, red, purple, and blue. The most affordable and frequently purchased is blue topaz that has received its color from treatment.

In 1812, Friedrich Mohs developed a set of 10 standard minerals that could be used to assign a relative hardness to minerals and other materials. Today, over 200 years later, his hardness scale is used by students and geologists throughout the world to identify mineral specimens.

What Color is Topaz?

Topaz occurs in a wide range of natural colors; however, most natural topaz is colorless. The most highly regarded colors are the reds and pinks, which receive their color from trace amounts of chromium. Chromium is also responsible for the color in violet and purple topaz.

 A variety is known as "imperial topaz" is especially valuable because people enjoy its reddish-orange to orangy-red colors, which often both occur in the same crystal. Most of the world's imperial topaz is found in Brazil. Topaz with natural blue color is very rare and valuable.

 Yellow, brown, and colorless topaz have lower values. These colors are often heated, irradiated, coated, and treated in other ways to alter their color.

Use of Topaz as a Gemstone

The name "topaz" and many language variants have been used for yellowish gemstones for at least two thousand years. At that time yellowish gems were called "topaz" in many parts of the world. Many of the earliest gem traders did not realize that these yellowish stones were actually different materials. Then, about two hundred years ago, people who traded in gems began to realize that these yellowish gems might be topaz, quartz, beryl, olivine, sapphire, or one of many other minerals. They also learned that topaz occurred in a wide range of colors other than yellow.  If you visited a jewelry store as recently as fifty years ago and asked to see topaz, you would likely have been shown gems that were in the colors range of yellow, orange, and brown.

Starting in the 1970s and 1980s, the most common color that you would be shown began to be blue. This blue color was usually produced by treatments that converted colorless topaz into a more marketable gemstone.

Sources of Topaz

Topaz is found in many locations worldwide where rocks like pegmatite and rhyolite are formed. Here, topaz is usually a minor mineral in terms of quantity, and a secondary mineral in terms of its time of formation. Brazil has been the world's most important source of topaz for decades. Almost all of the world's fine-quality imperial topaz is produced in the state of Minas Gerais in southeastern Brazil.

The Ouro Preto and Capao mines have been the most important sources of yellow, orange, pink, red, and violet topaz crystals for the gem and mineral specimen markets. Brazil is also the leading producer of colorless topaz, much of which is heat treated and irradiated to produce the colors of Swiss blue and London blue. Pakistan is a smaller but noteworthy source of pink, red, and violet topaz. Sri Lanka is a very important source of colorless topaz.

Other sources of topaz include Australia, India, Madagascar, Mexico, Myanmar,  amibia, Nigeria, Russia, and Zimbabwe. In the United States, some topaz is produced in Utah, where it was named the state gemstone in 1969.

Geologic Occurrence of Topaz

Topaz has a chemical composition of Al2SiO4(FOH)2. The fluorine in its composition is a limiting factor in its formation. Fluorine gas in concentrations high enough to form minerals only occurs in a few geologic environments.

Most topaz grows as crystals within the veins and voids of igneous rocks. This topaz is found in the cavities of a pegmatite, or in the vesicles and intergranular spaces of rhyolite. These topaz crystals grow during the late stages of magma cooling and while degassing releases the fluorine necessary for topaz crystal growth.

Precipitating in cavities, topaz sometimes develops nicely formed crystals. These crystals can have excellent clarity and can be used as a gem material. Many mineral collectors enjoy collecting gem-quality topaz crystals because they have the value of an excellent mineral specimen plus the value of gem material.

Topaz is also found as water-worn pebbles in stream sediments derived from the weathering of pegmatites and rhyolites. These are often produced by placer mining.