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 in igneous rocks (magmatic rocks) such as pegmatite and rhyolite, at an advanced stage of cooling. It is also found as water-worn pebbles in stream sediments derived from these igneous rocks.
Topaz is also a gemstone sold in a wide variety of attractive colours. Some of these colours are natural, while others are produced by treating pale or colourless topaz with heat, radiation or metal coatings.
Blue topaz is the most popular colour on the market today. Most is produced by treatment. Many people like it for its attractive colour 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 in almost every jewelry store.
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 is also used as a Mohs scale hardness index mineral with a hardness of 8. Every student who takes a physical geology course learns the hardness of topaz. Diamond, corundum and chrysoberyl are the only known minerals that are harder.
Topaz is available in a wide range of colours. The most valuable colours for use in jewellery are natural pink, orange, red, purple and blue. These colours are very rare.
The most common natural colours are colourless, pale yellow and brown. Although these colours are not important for use in jewellery in their natural state, they can be treated in different ways to produce much more desirable colours.
When allowed to grow in an unrestricted cavity, topaz forms orthorhombic crystals, often with striations parallel to the major axis of the crystal. It also has a distinctive basal cleavage that breaks to form vitreous fracture surfaces perpendicular to the major axis of the crystal. This cleavage makes topaz a more brittle gem than its hardness of 8 would imply. Topaz is very hard, but it is also brittle and splits easily.
Topaz has a density between 3.4 and 3.6. This is quite high for a mineral composed of aluminium, silicon and gaseous elements. This high density causes it to concentrate in deposits placed by river currents.
What colour is topaz?
Topaz is present in a wide range of natural colours. However, the most natural topaz is colourless. The most sought-after colours are reds and pinks, which get their colour from traces of chromium. Chromium is also responsible for the colour in violet topaz.
A variety known as "imperial topaz" is particularly interesting because people appreciate its colours ranging from orange to red-orange, which are often found in the same crystal. Most Imperial Topaz is found in Brazil. The natural blue topaz is very rare and precious.
Yellow, brown and colourless topaz have lower values. These colours are often heated, irradiated, coated and otherwise treated to alter their colour.
Use of topaz as a gemstone
The name "topaz" and many linguistic variants have been used for at least two thousand years in yellowish gemstones. At that time, yellowish gemstones were called "topaz" in many parts of the world. Many of the early gem dealers did not realize that these yellowish stones were actually different materials.
Then, about two hundred years ago, gem dealers began to realize that these yellowish gems could be topaz, quartz, beryl, olivine, sapphire, or one of many other minerals. They also learned that topaz came in a wide range of colors other than yellow.
If you had visited a jewelry store just fifty years ago and asked to see topaz, you would probably have been shown gems in shades of yellow, orange and brown.
Starting in the 1970s and 1980s, the most common colour you were shown began to be blue. This blue colour was usually produced by treatments that transformed colourless topaz into a more marketable gemstone.
Today, most of the topaz offered in jewellery shops in shopping centres and department stores at moderate prices have been processed in laboratories. Colourless topaz can be heated, irradiated and covered with thin layers of metal oxides to alter its colour.
Natural blue topaz is extremely rare and is usually pale blue. Today, almost all the blue topaz available in stores is colourless topaz that has been irradiated and then heated to produce a blue colour. "Swiss blue" and "London blue" are the trade names for two of the most common varieties of processed blue topaz on the market today.
Natural pink with violet topaz is also extremely rare, but these colours can also be produced in the laboratory. The starting point is a stone cut from a colourless topaz. It is first heated and then covered with a layer of metal oxide to produce the colour pink. If coated stones are worn in jewellery, the coating can wear away over time, thinly or in places on the stone, through abrasion.
Some topazes are coated with a metallic oxide which gives the stone a multicoloured iridescent lustre. These stones, called "mystical topaz", seem to change colour if the observer moves the stone under a light or changes the angle of observation. These coatings are also thin and can be worn during normal wear and tear.
Radioactive blue topaz?
The type of irradiation used to transform colorless topaz into blue topaz can cause slight radioactivity in the irradiated material. Fortunately, the level of radioactivity in topaz begins to decrease as soon as the treatment is completed. Eventually, the level of radioactivity will drop to a level that allows the topaz to be manipulated during manufacture and sold to the public as jewellery.
In the United States, the Nuclear Regulatory Commission requires that all irradiated gemstones be stored securely until their radioactivity decreases to a level that is safe for manufacture and sale. This is done to protect employees in the gemstone and jewelry industry and the public purchasing jewelry.
All companies that distribute recently irradiated gemstones in the United States must be licensed by the Nuclear Regulatory Commission. They must also conduct radiological checks of all safely stored materials to ensure that no gems are released until their radioactivity decreases to a level that poses no health risk.
The Nuclear Regulatory Commission provides detailed information on irradiated topaz and other gemstones on its website. They also have answers to frequently asked questions.
Is it dangerous to wear blue topaz?
NRC has no reason to believe that wearing irradiated gemstones can be harmful. No cases of irradiation have been reported. There is no safety reason to stop wearing blue topaz or any other irradiated gems.
Sources of topaz
Topaz is found in many places in the world where rocks such as pegmatite and rhyolite are formed. Here, topaz is generally a minor mineral in terms of quantity and a secondary mineral in terms of time of formation.
Brazil has been the world's most important source of topaz for decades. Almost all of the world's high-quality imperial topaz is produced in the state of Minas Gerais in southeastern Brazil. The Ouro Preto and Capao mines are the most important sources of yellow, orange, pink, red and purple topaz crystals for the gemstone and mineral sample 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 remarkable source of pink, red and violet topaz. Sri Lanka is a very important source of colourless topaz. Other sources of topaz include Australia, India, Madagascar, Mexico, Myanmar, Namibia, Nigeria, Russia and Zimbabwe. In the United States, topaz is produced in Utah, where it was named a state gemstone in 1969.
Treated Blue Topaz - A manufacturer's dream
A manufacturer preparing to supply a large retail chain often has difficulty finding a sufficient supply of gemstones. The company needs thousands of gems with consistent colour, clarity, cut and size. This will be a huge faceting job, but it can also be a huge sorting job if the gems change colour.
Colorless topaz is the ideal material for faceting gemstones of constant color and clarity. It is abundant, available in large, high clarity crystals and can be processed to a consistent blue color.
Caring for Treated Blue Topaz
The radiation and heat treatment used to produce the blue color in topaz is permanent, so you don't have to worry about discoloration of the gems when exposed to light. However, topaz has a perfect splitting direction that could separate if exposed to rough handling. It may also contain liquid-filled inclusions that can cause a gem to fracture when heated. Topaz should therefore be carefully cleaned with hot water and soap. Steam and ultrasonic cleaning should not be used.
11 things to know about Topaz
1. Topaz can be found in all the colours of the rainbow. The most valuable colour is red and is often called imperial topaz. Less than 1% of all gem quality topaz has this colour.
2. Topaz is one of the two designated birthstones for November. The amber version of topaz is the best known to be the November birthstone, since it is similar in appearance to the other November birthstone, citrine. Blue topaz is even considered by some to be a December birthstone (although there are already three designated birthstones for this month).
3. The ancient Greeks believed that topaz had the power to increase its strength in case of problems.
4. One of the best known topaz stones is a colorless topaz of 1680 carats located in the Portuguese crown. It was originally thought to be the largest diamond ever discovered until its true identity was discovered.
5. Topaz is the gemstone designated for the 4th and 23rd anniversaries. Blue topaz is reserved for the 4th anniversary, while imperial topaz is reserved for the 23rd anniversary.
6. When worn as a necklace, topaz was supposed to chase away sadness and strengthen the intellect.
7. The majority of topaz is found in Brazil. Russia, Germany, Zimbabwe and Nigeria are other remarkable places for this gemstone.
8. Topaz has been rated 8 out of 10 on the Mohs hardness scale for gemstones, making it a durable stone that can be worn daily without too much risk of damage.
9. There are two theories about the origin of the name topaz. The first is that the name comes from a small island in the Red Sea called Topazios. This island has never produced topaz gemstones, but peridot. In fact, before the invention of modern mineral detection methods, topaz was often confused with peridot. The other theory surrounding the origin of its name comes from the Sanskrit word "tapas" which means fire.
10. Pink topaz was first discovered in 19th century Russia. As the gem was highly coveted, only the tsar, his family and those to whom he had given it had the right to possess and wear the gem.
11. Topaz is associated with loyalty, friendship and fidelity, making it an ideal gift for a wedding or anniversary.