Red and intense pink are the most rare and most desirable colors for Topaz. A gem with
these colors will command a relatively high price. Bright orange color Topaz, also known as
Imperial Topaz, falls into the moderate price range and is easier to find. Blue Topaz, having
a low to moderate price range, is very popular, because a variety of shades, sizes and shapes
are available.
The true determinant for the evaluation of this precious stone will be the wearer's
preference. The intensity of color and the clarity of the stone will contribute to the value
of topaz as well, and should never be neglected.
Precious Topaz
The classical "precious topaz" is yellow or yellow to orange-brown in color. Sherry or Madeira
would best describe the most desirable and most valuable color.
Blue Topaz
Over the last 10 years or so, jewelers' windows have become filled with Blue Topaz, which is
very attractive and inexpensive. It has, to some extent, become a substitute for Ceylon
Sapphire. Blue Topaz does occur naturally, but almost all commercially available material is
produced from less attractive colors which are irradiated and heat treated to turn them blue.
This treatment produces a stable color, and normally the stones are not radioactive when they
are released on the market, although there have been cases where stones with an unsafe level
of radiation have been sold.
There are distinct hues of Blue Topaz, which arise as a result of the different treatments.
The most usual colors are known as "London Blue", "Swiss Blue" and "Sky Blue". These colors
were listed in order from the deepest to the palest colors.
Cleavage
Perfect cleavage is one of the notable attributes of Topaz. Because of the nature of its
crystal structure, Topaz has like one plane in which its bonds are relatively weak. If it
receives a sharp blow in the wrong place or direction, it can fairly easily break cleanly in
two. This is similar to the way in which large diamonds are cut, and should not be too great
a concern in normal jewelry use, once the stone is mounted.
Sources
The world's largest supplier of topaz is Brazil. However, Pakistan and Russia are now
emerging as the new sources for topaz supply. Topaz comes in a variety of shapes, colors
and sizes making it ideal for a wide variety of applications.
Technical Characteristics
Topaz is composed of Aluminium Fluosilicate, the fluorine (F) and the hydroxyl
(OH) can partly replace each other.
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Chemical Composition:
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Al2(OH,F)2SiO4 - Aluminium Fluosilicate
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Hardness:
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8
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Specific Gravity:
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3.50 - 3.60
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Refractive Index (R.I.):
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(Blue & White) 1.61 - 1.62
(Brown & Pink) 1.63 - 1.64
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Bi-refringence:
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(Blue & White) 0.010
(Brown & Pink) 0.008
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Optic Sign:
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Positive
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Optical Character:
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Biaxial
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Crystal Structure:
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Rhombic
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