henrihuman
Rough_Rock
- Joined
- May 30, 2001
- Messages
- 4
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In 1959 it was established that the majority (over 99%) of natural diamonds contain sub-microscopic nitrogen as an impurity within the carbon pattern. Such diamonds are termed ‘Type I’. Those diamonds which do not contain readily detectable nitrogen as an impurity are termed Type II.---Type II diamondsThese rare diamonds allow the passage of SWUV light and do not contain readily detectable nitrogen hence the Type II diamond atomic structure is more theoretically perfect than that of Type I diamond. As with Type I, Type II diamonds are sub divided. Some Type II diamonds conduct electricity and are termed Type IIb. They contain boron and mostly all are blue in colour. Type II diamonds lacking the impurity boron are termed Type IIa; they have the most perfect crystal structure thus are extremely transparent, often of excellent gem colour i.e. colourless, and have the greatest thermal conductivity. Type II crystals tend to be large and irregular in shape. A number of large famous diamonds, such as the Cullinan and the Koh-i-Noor diamonds, are of type IIa.