Abstract
Three historical ‘asteriated’ diamond slices present mixed-habit growth with contemporaneous lobe-shaped cuboid sectors and octahedral sectors. The lobe shape is explained by continuous variation of the relative growth rates. Nitrogen concentration in octahedral sectors is higher than in cuboid sectors, whereas hydrogen is incorporated mostly in cuboid sectors. The H-related IR peak at 3236 cm −1 peak, and the two peaks at 3050 and 3154 cm −1 (which may be completely absent from the spectra) are independent from the well-known 1405–3107 cm −1 system. Nitrogen aggregation during thermal history seems partially inhibited in cuboid sectors by the large amount of hydrogen, as platelets and N3 centres are present in octahedral sectors but not in cuboid sectors. Cuboid, H-rich growth sectors are thought to appear when the amount of hydrogen in the medium is too high to be incorporated in the octahedral sectors only. The definition of ‘H-rich diamonds’ is revisited. The first-order Raman peak at 1332 cm −1 is slightly growth-sector dependent; cuboid sectors show a sharper and more Lorentzian peak than octahedral sectors.
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