|The Very Highest Quality Topaz Information...|
Topaz is well known to be yellow, and in ancient times all yellow stones were called topaz. Nowadays we know better.
Topaz can also be colourless, blue, green, pink, orange or brown.
The classical precious topaz is yellow or yellow to orange-brown in colour. Sherry or Madeira (I suppose it goes well with the tapas!) would best describe the most desirable colour.
Blue Topaz - Treated Stones
In the last 10 years or so, jewellers' windows have become filled with blue topaz, which is very attractive and inexpensive, and has to some extent become a substitue for Ceylon sapphire. Blue topaz does occur naturally, but almost all commercially available blue topaz is produced from less attractive colours which are irradiated and heat treated to turn them blue. This treatment produces a stable colour, 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 we presume arise because of the different treatments. The most usual colours are known as "London Blue", "Swiss Blue" and "Sky Blue", we have listed these in order from the deepest to the palest colours.
Being male, this conjures up images of the Eva Herzigova poster, but it 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 topaz 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 jewellery use, once the stone is mounted. We experienced this first-hand on one occasion. We were showing a customer a number of loose topazes, and she dropped one a short distance onto a glass topped counter, with the result that we instantly had two topazes instead of one. Those of you with less than perfect cleavage can feel happy to know that it is not always a completely desirable feature.
Topaz is composed of Aluminium Fluosilicate, the fluorine (F) and the hydroxyl (OH) can partly replace each other.
|Chemical Composition and Name||Al2(OH,F)2SiO4 - Aluminium Fluosilicate|
|Refractive Index (Blue & White)||1.61 - 1.62|
|Refractive Index (Brown & Pink)||1.63 - 1.64|
|Bi-refringence (Blue & White)||0.010|
|Bi-refringence (Brown & Pink)||0.008|
|Other Optical Properties||Biaxial|
|Specific Gravity||3.50 - 3.60|
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