Growth versus dissolution

We will explain in the following sections what new information may be obtained from morphology, perfection, and homogeneity in diamond crystals, in addition to the geological, geochemical, petrological, and mineralogical data. 

A total of 364 crystal figures of diamond are reproduced in Goldschmidt s Atlas der Kristallformen [1] published in 1913-23. The figures are beautiful sketches of crystals, and they even include surface micro topographs some of these are shown in Fig. 9.2. 

The rounded forms of natural diamond crystals are commonly observed in crystals occurring both in alluvial deposits (secondary deposits) and in mother rocks 

Origin of rounded forms Growth model Dissolution model 

Center ross pattern Growth model Deformation model 

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Table 9.1 Growth versus dissolution controversies surrounding natural diamond crystals...

During crystal dissolution at constant rate, some authors used an equation similar to Equation 4-43b to extract D values. However, because of the opposite sign for crystal dissolution versus growth, the concentration profile would be... 

Indeed, a nearly parabolic dependence of surface film growth in exposure time was found for lithium and calcium in thionyl chloride solutions [33,34], In any event, the above description is only a first approximation. In reality, the films are not necessarily homogeneous, and, as described in the previous section, water contamination may play an important role, and possible dissolution-deposition cycles of the surface species, as well as their possible secondary reactions with solution species, may considerably distort the above parabolic dependence of / (film) versus t. 

Different from the dissolution of amorphous polymers is that of semi-crystalline ones. Dissolution of these polymers is much more difficult than that in the glassy state, as the enthalpy of melting has to be supplied by the solvent. Many solvents, which are able to dissolve tactic but glassy polymers, are unable to dissolve the same polymer in the crystalline state. Asmussen et al. (1965) have found that the velocity of dissolution of crystalline polymers as a function of temperature closely resembles the velocity of crystallisation versus temperature curves. Polymers formed at the highest rate of growth also dissolve at the highest rate. 

Murphy W. M., Oelkers E. H., and Lichtner P. C. (1989) Surface reaction versus diffusion control of mineral dissolution and growth rates in geochemical processes. Chem. Geol. 78, 357-380. 

The above equations may be applied to diffusion, dissolution or crystallization processes k can be taken as the relevant rate constant. For example, a plot of logX G versus T would give a so-called activation energy for crystal growth, E cryst log versus T gives EwiS8 log7) versus where... 

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