Topaz occurs in pegmatites, high-temperature quartz veins and in cavities in acid rocks such as granite and rhyolite and can be found associated with fluorite and cassiterite.
It can be found in the Ural and Ilmen mountains (Russia), the Czech Republic, Saxony, Norway, Sweden, Japan, Brazil, Mexico and the United States.
The rarest of them, the “imperial topaz” was first found in Russia, the same was found in Brazil for the first time, known as “Brazilian rubies”, in 1751.
The Urals was the site of the first deposits, which were exhausted during the Tsarist period.
It is found mainly in Brazil, in mines in Ouro Preto, Minas Gerais.
Topaz, due to its rarity and beauty, is one of the most valued stones today. In Portugal it can be found in the area of Gonçalo, Guarda;
History of the discovery of the Imperial Topaz
Discovered in the 18th century in the Ouro Preto region, imperial topaz was once very popular in Portugal, but is rarely used today.
Normally, when people talk about topaz, they think of the colour yellow or orange.
The name “topaz” is even mistakenly used for citrine and smoky quartz.
In fact, it was these colours that made topaz such a sought-after gem in the past.
Nowadays, however, it’s the blue colour that gives it popularity on a global scale, and this colour, as we know, is usually artificial and mostly obtained by irradiating colourless topazes.
More than two centuries ago, these colourless topazes were used in silver jewellery and were the origin of the commercial expression “minas novas” (new mines), which today has no gemological meaning.
It was therefore the yellow topazes, but especially the orange to almost red ones, that brought this mineral into the limelight of precious stones.
It was the second quarter of the 18th century and gold and diamonds were being sought out in the Minas Gerais region of Brazil.
It was in the region of Ouro Preto, so named because gold nuggets with a black patina were found there, that the first almost red topazes were discovered.
They arrived in Portugal with great pomp, and the most colourful specimens were nicknamed “Brazilian rubies”.
These gems were immediately integrated into the Portuguese jewellery of the time, as can be seen in the pieces that still exist, such as the Custody of the Patriarchal Cathedral of Lisbon and the resplendence of Senhor Santo Cristo dos Milagres in Ponta Delgada.
These show the presence of topazes of good colour and quality, alongside diamonds, rubies and emeralds, reflecting the esteem in which these stones were held in Portugal.
The documentation is also rich in allusions to topazes, specifically the inventory of jewellery taken from the Dukes of Aveiro in 1759, which includes several jewels with “topazes from Brazil”, the name by which these gemological varieties were known.
Regarding the nomenclature, it should be said that the expression “imperial topaz” dates back to the 19th century and may be linked to the figure of Dom Pedro II of Brazil, although there are references to the name being given to the Russian imperial family when pink and red topazes were discovered in the Urals.
The name “precious topaz” also appeared for the yellow varieties. Strictly speaking, the term “imperial topaz” is the commercial name for orange to red topazes.
One of the characteristics of imperial topazes is the colour and brilliance they offer when illuminated with incandescent light or, in particular, by candlelight, giving them a particularly attractive life, which may have been the basis of their appreciation in ancient times when lit by stearine wicks.
Today, it is still in the Ouro Preto region that almost all imperial topaz is produced, with the Vermelhão, Capão and Dom Bosco mines, for example, being famous for extracting tonnes of material.
It turns out that only a limited percentage is good enough to be used as a gem, with orange-coloured specimens of more than 20 carats being rare and those of an intense reddish colour of more than 5 carats being even scarcer.
Only in the more heavily coloured specimens is there any tolerance in the purity of the stones, such is their rarity. Having perfect cleavage, care is recommended in their setting and also in their cleaning and daily use.
The colour of imperial topazes is generally natural, with the exception of some pink specimens that owe their colour to heat treatment.
More recently, colourless topazes coated with metallic films have appeared on the market, giving them, for example, yellow to red colours, making them difficult to spot for the less cautious.
There are no known synthetic imperial topazes, but there are stones with a similar appearance, some of which are called “topaz” on the market, such as citrine and smoky quartz.
The same sometimes happens with the yellow and orange synthetic stones found, for example, in graduation rings.
In the current market in Portugal, imperial and yellow topazes have practically disappeared from jewellery shop windows, appearing from time to time in the windows of antique shops or auction houses, set in antique jewellery from the 18th and 19th centuries.
The popularity of topaz in Portuguese jewellery from this period could have been a motivating factor for finding market opportunities, but this has not been verified.
It may be that new creatives will be inspired by this historical and artistic heritage to give a new direction to one of Brazil’s most interesting gems.
Characteristics of the Topaz stone
Topaz is a fluorine-aluminium nesosilicate mineral with the chemical formula Al2(F,OH)2SiO4. It is widely used in jewellery and is classified as a precious stone;
It is a mineral that crystallises in the orthorhombic system and its crystals are mostly prismatic with or without pyramidal faces, often with a basal pinacoid.
It has perfect basal cleavage, which is why gems or other thin specimens must be held carefully to avoid cleavage faults appearing. The fracture is conchoidal and uneven.
When heated, yellow topaz often turns reddish-pink.
1. Types of Topaz
There is no specific type of this gemstone apart, of course, from the Imperial. Generally, they are differentiated by their colour, which can vary greatly. Therefore, the types of topaz are designated by the shade in which it is found.
2. Colours found
In this case, the topaz can be classified as swiss, london or sky, depending on its colour.
Blue topaz is a popular and sought-after stone that is difficult to find in nature, so traders often irradiate the clear topaz and then heat it to produce a blue topaz.
Blue topazes are more favoured because they resemble seawater, so most blue topaz is treated, but the price of blue topaz has decreased because it has been treated;
The Mohs Scale is able to quantify the hardness of minerals, i.e. their resistance to scratches, falls and other possible problems that could damage the stone. According to this index, Topaz is a gem with a “grade” of 8, qualifying it as an extremely solid and firm mineral.
To give you an idea, Diamond is in 1st position among the most durable stones, beating the number 10 on the Mohs Scale. Topaz is therefore an extremely firm mineral, second only to Ruby and Sapphire – both of which have a hardness level of 9.
This characteristic is usually called Relative Density, in which the weight of the piece is compared to the weight of the same volume of water. Thus, a material with a Relative Density of 3 has 3 times the weight of the same volume of water.
Topaz therefore has a density of 3.40-3.60. This value is often used to determine whether a stone is real, as this classification does not undergo any major changes due to the alternation of pieces, always following a fine line between the general aspects.
Like Relative Density, the refractive index is used extensively to check whether a gem is real or not. Furthermore, from this measurement it is possible to identify the origin of the gemstone, which varies in value according to its characteristics.
The gem in question has a refraction of 1.62 and 1.63.
In short, reflection refers to the speed of light in a vacuum and in a gemstone, which tends to be a little slower as the density of the jewel is greater than in a vacuum.
6. Possible treatments
- Thermal – changes the colour of some yellow, orange and brown topazes to pink or red.
- Irradiation – turns some colourless topazes brown or brownish green, this being the first stage in the production of treated blue topaz, which is then heat-treated, producing the blue colour in the irradiated stones.
- Temperature – rapid heating or cooling causes internal fractures; under strong heat it can alter or completely lose its colour.
- Daylight – some brown gems lose their colour under strong light.
- Chemicals – very slightly attacked by acids.
8. Synthetic Topaz Stone
Like all stones that are sought after by sellers and consumers, topaz is also manufactured synthetically, some in laboratories, some synthetically and some created, but when buying topaz jewellery you should always question its origin and at the same time ask whether the stone has been treated;
The colours most commonly found in nature are pink and red crystals. These are the most expensive colours of natural topaz, but brown topaz can be heat-treated to produce a pink stone;
Where and how to find Topaz
Brazil is a great reference point for this stone, as it is rich in this mineral, especially in the state of Minas Gerais.
It is also the country that imports the most of these stones, including the Imperial Topaz, which is currently only found in Brazil.
However, the most common colours can also be found in India, Australia, Germany, Mexico, Nigeria and the United States of America.
Consequently, the ways of extracting this precious gem vary from place to place, but the most common way is through gold mines.
This gem becomes even more elegant when included in the manufacture of rings, necklaces, pendants and earrings.
These jewellery pieces are sophisticated and have a shine that exudes elegance and fluidity. Because of this, they are high-priced pieces, but they can be made with smaller stones and have their cost reduced.
The price of adornments can vary depending on the colour of the item, what materials the artefacts are made from and the weight of the stone used.