Origin of name
“Amarelo” in the Portuguese language means “Yellow,” and therefore “Topaz Amarelo” simply means “Yellow Topaz.” This is an obvious reference to the color of this enormous gemstone, from which the name appears to have been derived. Yellow is one of the commonest colors in which topaz exists in nature, besides other colors such as brown, pale blue, and colorless. Golden-yellow, golden-orange, and golden-brown colors are most favored colors of topaz, and when these golden colors have a pink or red overtone they are known as imperial topaz, which can be quite costly.
Characteristics of the gemstone
The largest pear-shaped topaz in the world
The “Topaz Amarelo” yellow topaz is of Brazilian origin, the prime source of enormous topaz gemstones in the world. The weight of the rough “Topaz Amarelo” is not known, but the cut and polished gemstone weighed 9,600 carats. The cut of the topaz is a pear-shaped cut, and the clarity almost flawless. The exceptional color, cut , and clarity of the gemstone combined with its enormous size has made the “Topaz Amarelo” one of the famous gemstones in the world. In the list of famous topazes greater than 1,000 carats in weight the “Topaz Amarelo” occupies the sixth position. The list also shows that the “Topaz Amarelo” is the largest pear-shaped topaz in the world. It also shows that the “Topaz Amarelo” is the third largest topaz in the Programa Royal Collections.Please click here for the list of topazes greater than 1,000 carats in weight.
Chemical properties of topaz
Topaz belongs to the sub-class Nesosilicates, under the class of minerals called silicates, the most abundant mineral on the earth’s surface. It is a fluorosilicate of aluminum having the formula Al2SiO4(F,OH)2. In nesosilicates the SiO4 tetrahedra form isolated units, and form cross-linkages between long chains of aluminum octahedra composed of AlO4F2 or AlO4(OH)2. This type of structure can grow into enormous crystals, and this explains the enormous size of the “Topaz Amarelo” which weighs 9,600 carats.
Crystal system and crystal habit of topaz
Topaz crystallizes in the orthorhombic crystal system, and forms vertically striated prismatic crystals terminated by pyramidal faces.
What causes the high density, refractive index and hardness in topaz ?
Topaz has a high density, refractive index and hardness; all three properties being caused by the close packing of atoms and ions in the crystal. The hardness of topaz is 8 on the Mohs scale, and thus topaz is one of the hardest minerals in nature.
Why colorless and blue topazes have a slightly higher specific gravity than yellow, pink and red topazes ?
In the colorless and blue varieties of topaz there is more fluorine (F) than hydroxyl (OH) in the formula Al2SiO4(F,OH)2. In yellow, pink and red varieties of topaz the situation is vice versa, with more (OH) and less F. The density and refractive index of these varieties of topaz also change accordingly. The colorless and blue varieties of topaz have a slightly higher specific gravity than the yellow, pink and red varieties.
Specific gravities of yellow, pink and red topaz are as follows:-
yellow – 3.51-3.54 pink – 3.50 -3.53 red – 3.49-3.57
The specific gravities of colorless and blue topaz are as follows :-
colorless – 3.56-3.57 blue- 3.56-3.57
Why the refractive index of colorless and blue topazes are slightly lower than the refractive index of yellow, pink and red topazes ?
Again for the same reason given above colorless and blue varieties of topaz have a slightly lower refractive index than the yellow, pink and red varieties.
Refractive index of colorless and blue topazes :- 1.61 -1.62
Refractive index of yellow, pink and red topazes :- 1.63-1.64
The dispersion and luster of topaz
The dispersion of topaz which is 0.014 is very low, compared to diamond which is 0.044 and cubic zirconia which is 0.060. The “fire” of diamond and cubic zirconia is due to its high dispersion. Topaz having a low dispersion does not have the fire of diamonds, but, the lack of fire is somewhat compensated by the luster of topaz, which is adamantine (diamond-like) to vitreous (glass-like).
Pleochroism in topaz
Orthorhombic crystals normally show strong pleochroism, but topaz is an exception, as pleochroism is weak or absent. Some yellow varieties of topaz may show a weak yellow to pink dichroism.
Causes of color in topaz
Colorless topaz is pure topaz without any impurities. The common impurity found in topaz is iron and sometimes chromium, but iron does not impart any color directly to topaz. Instead, iron forms another intermediate species which can absorb a photon of visible light and jump to an excited state. This intermediate species is known as a color center. When the excited color center reaches the ground state, it gives out energy in the form of light of a particular wavelength and color. All varieties of colors in topaz are produced by color centers, except the pink and red variety, where chromium seems to be responsible for the color, like in rubies. Gemstones whose colors are imparted by color centers, are ideally suited for color change by irradiation and heat treatment. Hence the production of pink and red topaz by heat treatment and blue topaz by irradiation followed by heat treatment.
History of the “Topaz Amarelo”
Source of the topaz
“Topaz Amarelo” undoubtedly originated in Brazil, the premier source of enormous crystals of topaz in the world. In all probability the “Topaz Amarelo” originated in the state of Minas Gerais, which produces almost 80 % of the total annual production of gemstones in the country.
Minas Gerais which in the Portuguese language means “General Mines” is the name given by the Portuguese colonialists after the discovery of gold in 1693 and diamonds in the 1720s, in the region. Ouro Petro the capital city of Minas Gerais, where the gold mines were situated, became one of the biggest cities in the whole of America, during this period. But, within about 150 to 200 years the entire gold deposits in this region were exhausted. Even, the diamond deposits that were discovered in the 1720s were almost exhausted by the end of the 19th century, when South Africa became the most important source of diamonds in the world. After Brazil gained its independence in the early 20th century, steps were taken to exploit other mineral resources in the country, which included gemstones such as aquamarine, tourmaline, topaz, kunzite etc.
Topaz was discovered in the same mountainous area west of Ouro Petro, where gold was mined for almost 200 years. The 290 sq. km. topaz producing region, known as the topaz belt runs in the east-west direction, west of Ouro Petro. Presently, two mechanized mines in this belt are in active production. They are the Capao Mines, situated just outside Ouro Petro and the Vermelhao Mines, situated about 12 km. east of Capao. Other smaller mines employing traditional methods of mining are also operating in the area.
“Topaz Amarelo” is acquired by the Programa Royal Collections
It is not known where the rough “Topaz Amarelo” was cut and polished, but the finished gemstone, a pear-shaped, yellow, flawless topaz having a weight of 9,600 carats was acquired by the Programa Royal Collections, based in Madrid, Spain. The enormous gemstone was added to the Special Exhibitions Collection, that consisted of 20 gemstones, brought together mainly for their extraordinary size, extreme rarity or historical value combined with exceptional quality. This collection had a total weight of 117,000 carats, inclusive of the 9,600 carats, of the “Topaz Amarelo.” The twenty gemstones in the Special Exhibitions Collection are given in the following table.
The twenty gemstones of the Special Exhibitions Collection of the PRC arranged in descending order of weights
|2||Topaz Lua de Maraba||25.250||octagonal-cut||gray|
|5||Citrine Sol del Sur||8200||oval||orange|
|8||Ruby Star of Jaipur||4185||cabochon||red|
|10||Rutilated Quartz Cahimbo||3095||oval||light brown|
|11||Aquamarine Minas Gerais||2205||emerald||greenish-blue|
|12||Hiddenite Bello Horizonte||1875||rectangular||green|
|15||Emerald Corazon Verde||456.50||heart-shaped||green|
|16||Emerald Agra||350||Indian cut||green|
|18||Emerald Jaipur||220||Indian cut||green|
|19||Diamond Gris||103.47||round brilliant||gray|
|20||Diamond Green||32.80||round brilliant||green|
According to this table the “Topaz Amarelo” is the 3rd largest gemstone in the Special Exhibitions Collection, of the Programa Royal Collections.
The “Topaz Amarelo” also included in the Monographic Exhibition on Topaz
Even though the “Topaz Amarelo” permanently belongs to the Special Exhibitions Collection of the Programa Royal Collections, it is sometimes included in the single theme exhibition on Topaz known as “Imperial & Noble”, if and when requested by exhibitors. This collection consists of 54 topazes of all sizes, cuts and colors with a total weight of 90,000 carats, and is perhaps the largest collection of topaz gemstones in the world. Eight of these 54 topazes are of enormous size weighing more than 1,000 carats in weight. Like all other exhibits in the collection, the topaz monographic exhibition is also accompanied by educational display panels giving a wealth of information on topaz such as their origins and sources, chemical. physical and optical properties, and their uses throughout history, being a gemstone known to mankind since ancient times.
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1) Topaz – website of the Department of Geological Sciences, University of Texas, Austin.
2) Gem & Crystal Treasures – Peter Bancroft, (1984)
3) Web page on Topaz – International Colored Stone Association
4) The Mineral Topaz – Galleries .COM
5) Topaz- Mindat .ORG
6) Website of Programa Royal Collections – Madrid, Spain.