Diamond occurrence

It is implicit in all the preceding discussion that diamonds actually are formed in the mantle. We note that a type of diamond occurrence called carbonado is likely to be of crustal rather than mantle origin (Ozima Tatsumoto, 1997) these are not considered in connection with characterization of the mantle. 

Honda, M., Reynolds, J. H., Roedder, E., Epstein, E. (1987) Noble gases in diamonds Occurrence of solar helium and neon. J. Geophys. Res., 92, 12507-21. 

Pearson D. G., Davies G. R., Nixon P. H., and Milledge H. J. (1989) Graphitized diamonds from a peridotite massif in Morocco and implications for anomalous diamond occurrences. Nature (London) 338, 60—62. 

Pearson D. G. and Nixon P. H. (1995) Diamonds in young orogenic belts graphitised diamonds from Beni Bousera N. Morocco, a comparison with kimberlite-derived diamond occurrences and implications for diamond genesis and exploration. Africa Geosci. Rev. 3, 295-316. 

Honda M, Reynolds JH, Roedder E, Epstein S (1987) Noble gases in diamonds occurrences of solar-like helium and neon. J Geophys Res 92 12507-12521... 

Tin exists in two ahotropic forms white tin (P) and gray tin (a). White tin, the form which is most familiar, crystallizes in the body-centered tetragonal system. Gray tin has a diamond cubic stmcture and may be formed when very high purity tin is exposed to temperatures well below zero. The ahotropic transformation is retarded if the tin contains smah amounts of bismuth, antimony, or lead. The spontaneous appearance of gray tin is a rare occurrence because the initiation of transformation requires, in some cases, years of exposure at —40° C. Inoculation with a-tin particles accelerates the transformation. 

Tlie oval symbol represents a probability or failure rate. A diamond is an event that is not developed because the preparer did not know what to do or thought it insignificant. A house-top is an expected occurrence (probability of one). Rectangles identify and explain gates. 

Natural diamond, 8 519-528 applications, 8 527-528 microcrystals, 8 522 occurrence and exploration, 8 520-522... 

As an indication, however, of the limits of the Zintl interpretation and with reference to the prototypal NaTl structure, notice that the description of the filled tetrahedral structures given by Zintl cannot be considered valid generally (with all the elements). An example is the occurrence of this structure in compounds such as LiZn or LiCd in which the diamond-like framework of Zn and Cd atoms cannot obtain the four electrons necessary to give sp3, hybrids. 

Burns R. G. (1975). On the occurrence and stability of divalent chromium in olivines included in diamonds. Contrih. Mineral. Petrol, 51 213-221. 

Fig. 6. General geology, mineral occurrences, and diamond drillhole locations In the Long Lake area with a cross section corresponding to the line A-B, Illustrating the general geology beneath the surface (modified from Fyffe Pronk 1985).

That the bond density is also of significance for heavier atoms is evident from the occurrence of the spherical-atom forbidden (222) reflection of diamond and silicon, even at low temperatures where anharmonic thermal effects (see chapter 2) are negligible. The historical importance of the nonzero intensity of the diamond (222) reflection is illustrated by the following comment made by W. H. Bragg, in 1921 ... 

Vapor grown diamonds are sjmthesized by the CVD method under low-pressure conditions, for which diamond becomes unstable, and it is possible to obtain single crystals of micrometer size. Frequent occurrences of multiply twinned par-... 

C60 has not yet been detected in primitive meteorites, a finding that could demonstrate its existence in the early solar nebular or as a component of presolar dust. However, other allotropes of carbon, diamond and graphite, have been isolated from numerous chondritic samples. Studies of the isotopic composition and trace element content and these forms of carbon suggest that they condensed in circumstellar environments. Diamond may also have been produced in the early solar nebula and meteorite parent bodies by both low-temperature-low-pressure processes and shock events. Evidence for the occurrence of another carbon allotrope, with sp hybridized bonding, commonly known as carbyne, is presented. 

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