Home » Gemstones » Topaz


Topaz


A gemstone that occurs in a wide range of natural and treated colors.


Author: , Ph.D., GIA Graduate Gemologist


topaz crystals of various colors

Colored Topaz Crystals: A collection of topaz crystals of various natural colors - sherry, imperial, pink, and purple. Most topaz crystals are colorless. Most topaz in commercial jewelry has been heated, irradiated, or coated to improve its color. Specimens and photos by Arkenstone / www.iRocks.com

Table of Contents



What is Topaz?
Physical Properties of Topaz
Use of Topaz as a Gemstone
Topaz Treatments
Radioactive Blue Topaz?
Geologic Occurrence of Topaz

What is Topaz?

Topaz is a rare silicate mineral with a chemical composition of Al2SiO4(F,OH)2. It usually forms in fractures and cavities of igneous rocks such as pegmatite and rhyolite, late in their cooling history. It is also found as water-worn pebbles in stream sediments derived from those igneous rocks.

Topaz is also a well-known gemstone sold in a wide variety of attractive colors. Some of these colors are natural, while others are produced by treating pale or colorless topaz with heat, radiation, or metallic coatings.

Blue topaz is the most popular color in the market today. Most of it is produced by treatment. Many people like it because of its attractive color and low price.

Topaz is a traditional birthstone for the month of November, which contributes to the gem's popularity. Topaz jewelry can be found for sale in almost every jewelry store.



Physical Properties of Topaz

Chemical Classification Silicate.
Color Natural colors include: colorless, yellow, orange, brown, red, pink, blue, green. Occurs in a wide range of treated colors, most often blue.
Streak Colorless - harder than the streak plate.
Luster Vitreous.
Diaphaneity Translucent to transparent.
Cleavage Perfect basal cleavage.
Mohs Hardness 8
Specific Gravity 3.4 to 3.6
Diagnostic Properties Hardness, prismatic crystals, sometimes striated, cleavage, specific gravity.
Chemical Composition Al2SiO4(F,OH)2
Crystal System Orthorhombic.
Uses Gemstone, Mohs hardness index mineral.

Physical Properties of Topaz

One of the best-known physical properties of topaz is its hardness. It has a hardness of 8 on the Mohs hardness scale, making it the hardest silicate mineral. It also serves as the Mohs hardness scale index mineral for a hardness of 8. Every student who takes a physical geology course learns about the hardness of topaz. Diamond, corundum, and chrysoberyl are the only commonly-known minerals that are harder.

Most topaz is colorless to milky. Yellowish and brownish colors are also common. Natural pink, orange, red, purple, and blue topaz are rare and valuable if they are of gem quality.

When allowed to grow unrestricted, topaz forms orthorhombic crystals, often with striations that parallel the long axis of the crystal. It also has a distinct basal cleavage that breaks perpendicular to the long axis of the crystal. This cleavage makes topaz a more fragile gemstone than its hardness of 8 would imply. Hardness is the resistance to being scratched, but the ability to resist breakage is a property known as tenacity.

Topaz has a specific gravity that ranges between 3.4 and 3.6. This is quite high for a mineral composed of aluminum, silicon, and gaseous elements.



Comet Tail Inclusion in Topaz

Comet Tail Inclusion in Topaz: It looks like a comet flying through a gemstone. Instead it is a tiny crystal of an unidentified mineral that started to grow on the surface of a much larger topaz crystal. The tiny crystal made it difficult for the topaz below it to grow properly - it had become an obstacle to growth. As the topaz crystal expanded, it pushed the tiny crystal in the direction of growth, and a wispy stream of inclusions within the topaz was the result.

topaz treatment methods

Topaz Treatment Methods: Colorless topaz, also known as white topaz, (top left) can be irradiated and heated to produce gems with a blue color (top right). Irradiation alone can produce a pale pink color (bottom right). Coating with certain metallic oxides can produce a vivid pink color (bottom left). Most topaz in commercial jewelry today is colorless material that has been heated, irradiated, or coated to improve its 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 fifty years ago and asked to see topaz, you would likely be shown gems that were in the color 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.

mystic topaz

"Mystic" Topaz: Some topaz is heated and then coated with a metallic oxide to change its color or to produce an iridescent effect. These treatments are sold under the trade name of "mystic topaz." These materials are simply clear topaz with a coating that might not be very durable.

Topaz Treatments

Today most topaz offered in mall and department store jewelry stores at low to moderate prices has been treated in a laboratory. Colorless topaz can be heated, irradiated, and coated with thin layers of metallic oxides to alter its color.

Natural blue topaz is extremely rare and is usually pale blue. Almost all of the blue topaz offered in stores today is colorless topaz that has been irradiated and then heated to produce a blue color. "Swiss blue" and "London blue" are trade names for two of the most common varieties of treated blue topaz seen in today's market.

Natural pink to purple topaz is also extremely rare, but these colors can also be produced in a laboratory. The starting point is a stone cut from colorless topaz. It is first heated and then coated with a layer of metallic oxide to produce the pink color. If coated stones are worn in jewelry, over time the coating can wear thin or wear through at points on the stone where abrasion occurs.

Some topaz is coated with a metallic oxide that gives the stone a multicolored iridescent luster. These stones, known as "mystic topaz," appear to change color if the observer moves the stone under a light or changes the angle of observation. These coatings are also thin and can be worn through during wear.

Swiss Blue, London Blue topaz

Blue Topaz: Faceted ovals of two colors of blue topaz that are popular today. On the left is a "Swiss Blue" topaz weighing 2.02 carats. On the right is a "London Blue" weighing 2.26 carats. Both stones were colorless topaz mined in Brazil. After faceting they were irradiated and heated to produce the blue colors. Topaz with treated blue color is the most common color of topaz in commercial jewelry today.

Quoted from The Nuclear Regulatory Commission’s FAQ:
Is it dangerous to wear blue topaz?
The NRC has no reason to believe that wearing irradiated gemstones can be harmful. There have been no reported cases of anyone being harmed by wearing them. There is no safety reason to stop wearing blue topaz or any other irradiated gems.

Do I need a license to sell blue topaz or other irradiated gems?
Probably not. NRC regulations cover material made radioactive in a nuclear reactor or linear accelerator. The initial transfer of these materials must be done under an NRC distribution license. Once the radioactivity levels fall below certain limits, the materials become "exempt" from further regulation. This means no license is needed to buy or to resell them. So individual jewelers do not need to be licensed as long as they receive their stones from an NRC licensee.


Radioactive Blue Topaz?

The type of irradiation used to transform colorless topaz into material with a blue color can cause some irradiated topaz to become slightly radioactive. Fortunately, the radioactivity level of the topaz begins to decline as soon as treatment is complete. It eventually declines to a level that is safe for the topaz to be handled during manufacturing and be sold to the public in jewelry.

In the United States, the Nuclear Regulatory Commission requires all irradiated gems and gem materials to be securely stored until their radioactivity decays to a level that is safe for manufacturing and sale. This is done to protect employees of the gem and jewelry industry and the jewelry-buying public.

All companies who distribute newly irradiated gems in the United States must be licensed by the Nuclear Regulatory Commission. They must also conduct radiological surveys of all materials in secure storage to be sure that no gems are released until their radioactivity declines to a level that will not pose any health risks.

The Nuclear Regulatory Commission has detailed information about irradiated topaz and other gemstones on their website. They also have answers to frequently asked questions. Two answers that we believe will be of interest to our readers are quoted in the box on this page. You can read the rest by visiting the NRC website.

Topaz Mountain Rhyolite

Topaz Mountain Rhyolite: Outcrop of stratified tuff of the Topaz Mountain Rhyolite, filling a paleovalley. These valley fills were once thought to be deposited by water, but now many of them are believed to have been deposited by ground surges of hot ash. The Topaz Mountain Rhyolite has many vuggy areas, which often contain champagne-colored topaz crystals. Located in western Utah. USGS image.

Mineral collection

The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties. Inexpensive mineral collections are available in the Geology.com Store.

Geologic Occurrence of Topaz

Topaz has a chemical composition of Al2SiO4(F,OH)2. The fluorine in its composition is a limiting factor on 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 then 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. Especially attractive crystals of topaz are popular with mineral collectors. They have the value of a mineral specimen and the value of a 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.

Topaz is found in many locations worldwide where rocks like pegmatite and rhyolite are formed. It is only a minor mineral at these locations, and it is considered to be a rare mineral on the basis of its general abundance.

Brazil is the leading source of gem-quality topaz today. Sri Lanka is another important producer. Small amounts of topaz are produced in Nigeria, Australia, Pakistan, Russia, India, Zimbabwe, Madagascar, and Namibia. In the United States, Utah named topaz as its state gemstone in 1969.



More Gemstones
  Diamond
  100+ Gems
  Pictures of Opal
  Ruby and Sapphire
  Emerald
  Extraterrestrial Gems
  Amethyst
  United States Gemstones

geology store

Find Other Topics on Geology.com:


Rocks
Rocks: Galleries of igneous, sedimentary and metamorphic rock photos with descriptions.
Minerals
Minerals: Information about ore minerals, gem materials and rock-forming minerals.
Volcanoes
Volcanoes: Articles about volcanoes, volcanic hazards and eruptions past and present.
Gemstones
Gemstones: Colorful images and articles about diamonds and colored stones.
General Geology
General Geology: Articles about geysers, maars, deltas, rifts, salt domes, water, and much more!
Geology Store
Geology Store: Hammers, field bags, hand lenses, maps, books, hardness picks, gold pans.
Earth Science Records
Earth Science Records: Highest mountain, deepest lake, biggest tsunami and more.
Diamond
Diamonds: Learn about the properties of diamond, its many uses, and diamond discoveries.