Classification of Diamonds

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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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. 

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) -. 

Many attempts at classifying solvent extraction systems have been made. Thus Diamond and Tuck [20] have described a classification of the solutes that can be separated by solvent extraction. 

Abstract Chronological studies of kimberlite-host rocks in the diamondiferous Buffalo Head Hills kimberlite field of north-central Alberta facilitate new interpretation of the nature, timing and sequence of kimberlite eruptions in northern Alberta. Three different emplacement episodes are recognized in association with volcanic and intrusive activity Late Cretaceous ( 88-81 Ma) Smoky Group equivalent intra- and extra-crater facies, Late Cretaceous and Paleocene ( 81 and 64 Ma) intrusion of sills or dykes, and Paleocene ( 60 Ma) Paskapoo Formation equivalent intra-crater facies. These specific periods of magmatism correspond to characteristic intra-field features such as spatial distribution, rock classification and diamond content. 

The classification and naming by Dana [9], [lO] and Orlov [11] of diamond forms... 

Table 9.3 Morphology of diamond Classification by Dana and Orlov...

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. 

A.H. Deutchman and R.J. Partyka (Beam Alloy Corporation observe, "Characterization and classification of thin diamond films depend both on advanced surface-analysis techniques capable of analyzing elemental composition and microstructure (morphology and crystallinity), and on measurement of macroscopic mechanical, electrical, optical and thermal properties. Because diamond films are very thin (I to 2 micrometers or less) and grain and crystal sizes are very small, scanning electron microscopy... 

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. 

Two major classifications for diamond crystals are mono- or single crystalline and polycrystalline. The monocrystalline diamond particles tend to have more uniform surfaces and sharp edges. The abrasiveness of the monocrystalline diamond is mainly governed by its particle size. In the case of polycrystalline diamond, it is sometimes determined by the packing arrangement and the interaction of these single crystals that are related to friability [84]. Friability is defined as the readiness of a substance to crumble and form fine particles or fibers under the application of external pressures. 

The carbon isotopic composition of diamonds has been studied for many years (e.g., Galimov etal., 1978 Deines, 1980 Galimov, 1984). These early studies attempted to correlate diamond properties such as color and form with carbon isotopic composition in some form of classification... 

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