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
|
S/N |
Name |
Carat Weight |
Cut |
Color |
|
1 |
Topaz El-Dorado |
31,000 |
emerald |
yellowish-brown |
|
2 |
Topaz Lua de Maraba |
25.250 |
octagonal-cut |
gray |
|
3 |
Topaz Amarelo |
9600 |
pear |
yellow |
|
4 |
Topaz Azul |
8225 |
oval |
blue |
|
5 |
Citrine Sol del Sur |
8200 |
oval |
orange |
|
6 |
Garnet Giant |
8175 |
ball-cut |
red |
|
7 |
Citrine Soledade |
6705 |
emerald |
orange |
|
8 |
Ruby Star of Jaipur |
4185 |
cabochon |
red |
|
9 |
Garnet Mocambique |
4100 |
ball-cut |
unknown |
|
10 |
Rutilated Quartz Cahimbo |
3095 |
oval |
light brown |
|
11 |
Aquamarine Minas Gerais |
2205 |
emerald |
greenish-blue |
|
12 |
Hiddenite Bello Horizonte |
1875 |
rectangular |
green |
|
13 |
Kunzite Aracuai |
1490 |
oval |
pink |
|
14 |
Aquamarine Azul |
1129 |
emerald |
blue |
|
15 |
Emerald Corazon Verde |
456.50 |
heart-shaped |
green |
|
16 |
Emerald Agra |
350 |
Indian cut |
green |
|
17 |
Sapphire Star |
243.50 |
cabochon |
blue |
|
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.
Related :-
1)
American Golden Topaz.
2)
Famous cut and uncut topaz gemstones.
3)
El-Dorado Topaz.
4) Lua de Maraba Topaz.
References :-
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.
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