Diamonds type classification

The classification of amorphous carbon films according to carbon bond type and hydrogen content can be represented in a triangular diagram, Fig. 6 [e.g., 70]. The comers at the base of the triangle correspond to graphite (100% sp carbon) and diamond (100% sp carbon). The apex represents 100% H, but the upper limit for formation of solid films is defined by the tie line between the compositions of polyethene, -(CH2) -, and polyethyne, -(CH) -. 

Although Dana [9], [10] and Orlov [11] classified diamond crystals broadly into two types, single and polycrystalline, we can also construct a classification (given in Table 9.4) based on the preceding analysis. By this classification we are able to correlate the morphology of diamonds with their growth conditions and growth histories. 

As for hydrides, borides, and carbides, different types of nitrides are possible depending on the type of metallic element. The classifications of nitrides are similarly referred to as ionic (salt-like), covalent, and interstitial. However, it should be noted that there is a transition of bond types. Within the covalent classification, nitrides are known that have a diamond or graphite structure. Principally, these are the boron nitrides that were discussed in Chapter 8. 

The P-type versus E-type paragenetic classification of diamonds based on their inclusions is introduced in Section 2.05.4.1.3. The geochemical basis for this fundamental difference between inclusion types is discussed in review articles by Meyer (1987), Harris and Gurney (1979), Gurney (1989), and Kirkley et al. (1991), summarized in brief here and discussed in the context of newer SIMS trace-element data on inclusions. Meyer (1987) points out the importance of inclusions in diamonds for the study of the mantle. First, inclusions are the chief way to understand the relationship of diamonds to their mantle host lithologies. Second, inclusions often represent pristine, geochemically unaltered samples that are not subject to the chemical re-equilibration and alteration that affects the minerals in xenoliths and macrocry sts. 

Diamond has the highest thermal conductivity, the value depending on the classification of the diamond. It is highest for a Type Ila diamond (up to 1.5 X lO Wm- K- ). The linear... 

No two diamonds have exactly the same composition and properties, and any number of classification schemes can be devised. However only one classification is universally accepted. It is based on the nature and amount of impurities contained within the structure and consists of four types. These types, their origin, and their effect on optical and other properties are summarized in Table 11.2 (some diamonds may consist of more than one type). 

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