Is dispersed nickel in natural diamonds associated with cuboid growth sectors in diamonds that exhibit a history of mixed-habit growth?

Defects in a mixed-habit Yakutian diamond: Studies by optical and cathodoluminescence microscopy, infrared absorption, Raman scattering and photoluminescence spectroscopy

“…Later, a combined morphological, optical and X-ray topographic study by Welbourn et al [7] indicated that the output of the Jwaneng Mine, Botswana, contained about 8% mixedhabit specimens, an unusually high frequency. A recent finding of a mixed-habit core within a diamond originating from the Canadian Snap Lake kimberlite [8] illustrates the world-wide occurrence of this growth behaviour.…”

“…Following Bristol practice, CL topographs of 1137 were recorded by direct photomicrography of the crystal placed inside the SEM specimen chamber with the surface of interest flooded with a stationary electron beam [8]. The relative intensities of the many spectral components in the CL emissions depend upon incident electron energy, specimen current density and specimen temperature.…”

“…In natural diamonds the three features most studied are the absorption bands in the energy range below 1340 cm À1 that show the concentration of N impurity and its apportionment between A and B defects, the B 0 peak at $1365 cm À1 due to the well-known 'platelet' defects on {1 0 0} and a few sharp lines at higher energy, principally the 3107 cm À1 line, now established as due to bound hydrogen in the diamond structure [8,[12][13][14][15][16]. Earlier IR absorption measurements [11] on 1137 disclosed some interesting properties: a very high B-defect to A-defect ratio everywhere except in the shell zone, and noteworthy presence of the 3107 cm À1 line, mainly in the core, positively correlated with N concentration there.…”

Nitrogen isotope systematics and origins of mixed-habit diamonds

“…In reality both of these arguments are probably overly simplistic; factors like the partitioning of nitrogen into other crystallizing phases, their isotopic fractionation factors, as well as the oxygen fugacity, pressure and temperature conditions probably all play a role. The study of mixed-habit diamonds (Welbourn et al, 1989;Rondeau et al, 2004;Lang et al, 2004;Zedgenizov & Harte, 2004;Howell et al, 2012;2013a) demonstrate differences in nitrogen concentrations between different growth sectors that grew from the same fluid at the same time. This implies that the nitrogen partition coefficient between diamond and the source fluid/melt is not only controlled by thermodynamic or kinetic processes, but simple crystallography and growth mechanisms can also play a role.…”

“…Nitrogen concentrations in mixed habit diamonds are often very high (900 ->2000 ppm) and N is preferentially partitioned into the octahedral sectors; with enrichment ranging from 107 -157 % relative to the cuboid sectors (Welbourn et al, 1989;Rondeau et al, 2004;Lang et al, 2004;Zedgenizov & Harte, 2004;Howell et al, 2012;2013a).…”