Colour: Colourless, yellow, orange, red, red-brown, light to dark blue, pink-red, violet, light green Colour of Streak: White
Moh’s hardness: 8
Density or Specific Gravity: 3.49-3.57
Cleavage: Perfect
Chemical composition: Al2SiO4(F,OH)2
Refractive Index: 1.609-1.643
Reflective Index: 29-32
Dispersion: 0.0014(0.008)
Transparency: transparent to translucent

Topaz: Introduction
The topaz, also known as the November  and the gemstone for 4th, 19th, and 23rd years of marriage, comes in a wide range of colours but usually is yellow and can also be colourless.  The topaz is also the state gemstone for United States state of Utah.  The topaz derives its name from the Sanskrit word tapas meaning “fire” or the Greek word topazios meaning “to seek”.  On the Mohs scale, the topaz rates an 8.  Only diamonds and corundum are harder than Topaz.

Topaz: History
The exact discovery of the name of topaz was never really verified.  As stated in the introduction it either came from the Greek or Sanskrit.  The Greek philosopher, Pliny derived the name topazios after the island of Topazos (now known as the Island of St John), which is a small island off the Red Sea, where it is first stated that he discovery of topaz was made.  Historians believe that the topaz discovered at the island was not in fact topaz but the gemstone, peridot. 

The topaz has been known for its metaphysical properties.  The Indians believe that the topaz can be used as a talisman for health, caution, sagacity, and prevention of death.  The Egyptians believe that the yellow topaz was filled with the golden glow of the mighty sun god Ra.  They also used these stones as a talisman against harm.  The Romans associated topaz with Jupiter, who is also the god of the sun, wore topaz as a talisman from diseases, also to protect its wearer against perils and dangers in travelling, injuries from burns and scalds, and to avert pain of the chest and bowels.  Topaz was one of the stones in the 'Breastplate of Judgment' of Aaron, who was the brother of Moses and leader of an old Israeli tribe, described in the bible (Exodus: xxviii, 15-30).  Historically, topaz has been thought to give long life, good looks and intelligence. It is also thought to given protection from poison, disease and sorcery.  In 1740, the “Braganza” diamond (1,640 carats) was found in Ouro Preto, Brazil. It was set in the Portuguese crown, and was thought to be the largest diamond ever found. The fact that it was a diamond was never confirmed, and it is now believed to have been a colourless topaz.

Topaz: How is it formed?
Topaz is formed from gas and volatiles trapped in freezing granite. When found topaz crystals are isolated in pockets and are often very large.  This mostly occurs in cavities in lava and gigantic rocks.  Topaz is formed inside igneous rocks such as pegmatites and alluvial deposits.  This can be found in fluorite and cassiterite areas such as the mountains of Russia, Afghanistan, Sri Lanka, Czech Republic, Germany, Norway, Pakistan, Italy, etc.  
Compared to other minerals, topaz is relatively resistant to weathering and stream abrasion. These characteristics enable it to be found in the stream sediments derived from the weathering of topaz-bearing rocks. It is sometimes produced by placer mining.

Topaz: Colour
The majority of topaz is colourless and is called white topaz. The next most abundant colour of topaz is blue and green. The most frequently seen stones in jewellery are the shades yellow or sherry brown, and pink. Clear, pink, blue and honey-yellow varieties of topaz are especially valued. The most sought after and expensive colours are called “imperial topaz.” In the past, it was thought that all yellow gems were topaz and that all topaz was yellow. We now know topaz varies in colour from pale blue and colourless, to yellow, orange, brown and pink. The pink stones so popular in Victorian jewellery were produced by heat-treating golden-brown topaz from Brazil.

Blue topaz is a very popular gemstone and is rarely formed in nature. Most of the blue topaz on the market is treated. Unfortunately there is no way yet to determine which stones have been treated and which are natural. Although blue topaz has not been manufactured synthetically on a commercial scale, a completely natural looking blue coloration has been produced in colourless topaz by means of irradiation with gamma rays. This practice is regarded as legitimate in the trade, and is becoming increasingly widespread. It is one of the reasons for the present abundance of blue topaz in the trade.

Topaz: Treatment and Synthetic
As stated, blue topaz is a very popular gemstone but since it is very rarely found many treatments have been used.  This is the reason of the decline in recent years of blue topaz.  The following are ways people have treated or enhanced the quality of topaz.

Heat: This is a common method used in most gemstones.  Topaz has been heat treated to improve colour for decades, maybe even centuries.  This method has been used mostly to create blue, pink and red topaz, which are the most popular.

Irradiation: Irradiating topaz was a technique that was established many years ago to produce blue topaz.  Nearly all of the blue topaz on the market today has been irradiated in this way.  In Europe this treatment is controversial and on its way to being banned because of the possible residual radioactivity of the gemstones.

Diffusion: Another method of improving the colour of topaz involved coating the colourless topaz with a specific chemical and then heating it at very high temperatures.  Only the surface layer of the gemstone is affected while the centre remains colourless (you would not be able to tell unless you cut it in half). This is a relatively durable treatment.

Coating: Some topaz gemstones are treated with an extremely thin film of mineral or metallic materials and then placed in a vacuum.  This process creates  a wide variety of irridescent, eye catching colours.  They are called "Mystic Topaz", and new terms are coined every week.

Synthetics: Synthetic topaz is not very prevalent on the market because natural topaz is so available.  In fact, synthetic topaz can be found at the same price if not more expensive than natural topaz. Most jewellers will specify whether it is synthetic.
Imitation: Topaz is imitated by quartz (citrine) and glass.  It can be distinguished from these by a scratch test, since topaz is harder than both of these materials.  If you rub a piece of quartz against a topaz, the quartz will scratch but the topaz will not.

Information supplied By IGEM Instruments