TY - JOUR
T1 - Microstructural observations of polycrystalline diamond
T2 - A contribution to the carbonado conundrum
AU - De, Subarnarekha
AU - Heaney, Peter J.
AU - Hargraves, Robert B.
AU - Vicenzi, Edward P.
AU - Taylor, Patrick T.
N1 - Funding Information:
We would like to thank D. Johnson, N. Yao, and D. Yates for their help with sample preparation and analytical work. We also thank J. Milledge for providing us with the Brazilian carbonado sample. We thank R. Hough, D. Peacor, and S. Haggerty for their constructive reviews of the manuscript. Correspondence and request for materials should be addressed to S. De (E-mail: [email protected]). This work was supported by NSF grant EAR97-06143. [CL]
PY - 1998/12/30
Y1 - 1998/12/30
N2 - The formation mechanism of carbonado, a polycrystalline variety of diamond, remains unresolved. Here we report a microstructural analysis of systematic defects and inclusions in carbonados from Brazil and the Central African Republic (CAR). Transmission electron microscopy (TEM) has revealed the presence of pervasive defect lamellae in both the CAR and Brazilian carbonados that are distinct from planar defects observed in synthetic polycrystalline diamond (PCD). Analyses of included minerals by energy dispersive spectroscopy (EDS) yielded strong evidence for metallic Fe, Ti, and Si, as well as SiC and Fe-Cr alloys, within the diamond matrix. Our results offer strong evidence for a close genetic relationship between Brazilian and Central African carbonados, suggesting formation within a united landmass during the late Archaean. The data do not preclude carbonado nucleation by meteoritic impact, though this issue remains contentious. The role of water in the growth of carbonado merits further exploration.
AB - The formation mechanism of carbonado, a polycrystalline variety of diamond, remains unresolved. Here we report a microstructural analysis of systematic defects and inclusions in carbonados from Brazil and the Central African Republic (CAR). Transmission electron microscopy (TEM) has revealed the presence of pervasive defect lamellae in both the CAR and Brazilian carbonados that are distinct from planar defects observed in synthetic polycrystalline diamond (PCD). Analyses of included minerals by energy dispersive spectroscopy (EDS) yielded strong evidence for metallic Fe, Ti, and Si, as well as SiC and Fe-Cr alloys, within the diamond matrix. Our results offer strong evidence for a close genetic relationship between Brazilian and Central African carbonados, suggesting formation within a united landmass during the late Archaean. The data do not preclude carbonado nucleation by meteoritic impact, though this issue remains contentious. The role of water in the growth of carbonado merits further exploration.
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U2 - 10.1016/S0012-821X(98)00229-5
DO - 10.1016/S0012-821X(98)00229-5
M3 - Article
AN - SCOPUS:0032583373
SN - 0012-821X
VL - 164
SP - 421
EP - 433
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 3-4
ER -