Geochemistry International

, Volume 54, Issue 10, pp 882–889 | Cite as

Relationships between textural and photoluminescence spectral features of carbonado (natural polycrystalline diamond) and implications for its origin

  • Hidemi IshibashiEmail author
  • Hiroyuki Kagi
  • Shoko Odake
  • Hiroyuki Ohfuji
  • Hiroshi Kitawaki


Field Emission SEM (FESEM) textural observations, crystal size distribution (CSD) analyses, UV-excited luminescence imaging, and photoluminescence (PL) microspectroscopy excited by 488 nm laser were conducted on two texturally contrasting samples of carbonado, a kind of natural polycrystalline diamond from the Central African Republic (CAR). The investigated carbonado samples A and B show extremely different textures: sample A is made up of faceted crystals accompanied by abundant, small rectangular pores, whereas sample B has a granular texture with coarser crystals and scarce, large pores. Diamond crystals smaller than 2–3 µm are enriched in sample A but depleted in sample B. These textural features indicate that sample B diamonds were annealed under thermodynamically stable P–T conditions. The pore characteristics indicate that fluid permeability was higher for sample A than sample B. Photoluminescence (PL) spectra indicate that samples A and B correspond to Group A and B carbonados in the classification of Kagi et al. (1994), respectively, so that sample A reveals emissions from the H3 center without any N–V0 derived emission at 575 nm, whereas sample B shows emissions from the 3H center and the N–V0 defect. In addition, UV-excited luminescence images and photoluminescence spectra for sample B indicate that the rims of diamond crystals within several microns of a pore show luminescence features similar to those of Group AB carbonados (Kagi et al., 1994), indicating that this Group AB material was formed from Group B by irradiation from pore-filling, radioactive-element-bearing materials at a low temperature. The extent of the low-temperature irradiation is considered to depend on fluid permeability, and the Group A material was strongly irradiated due to its permeable texture whereas the Group B material was not significantly irradiated due to its less permeable granular texture. These results indicate that Group B carbonados have retained their original PL spectral features produced under high pressures and temperatures at mantle depths.


carbonado diamond photoluminescence texture CSD 


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Copyright information

© Pleiades Publishing, Ltd. 2016

Authors and Affiliations

  • Hidemi Ishibashi
    • 1
    Email author
  • Hiroyuki Kagi
    • 2
  • Shoko Odake
    • 3
  • Hiroyuki Ohfuji
    • 4
  • Hiroshi Kitawaki
    • 5
  1. 1.Department of Geoscience, Faculty of ScienceShizuoka UniversityShizuokaJapan
  2. 2.Geochemical Research Center, Graduate School of ScienceUniversity of TokyoTokyoJapan
  3. 3.Gemological Institute of America (GIA)TokyoJapan
  4. 4.Geodynamics Research CenterGraduate School of Science, Ehime UniversityTokyoJapan
  5. 5.Central Gem LaboratoryTokyoJapan

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