View Full Version : Carbonado.

2018-Sep-11, 02:04 PM
A hard black diamond found in south america and Africa. Apparently from space. It might be from supernova. I am interested as I wonder if white dwarfs might give off surface material when hit by supernove neutrinos, the stuff being spalled from the other side of the star. Finding this infomation caused me to fall into a brown study thinking about the hundreds of thousands of geologists who have been investgating material on the surface of this planet these past few hundred years. Flagging up this stuff as interesting. We are all richer for the knowledge!

2018-Sep-11, 04:11 PM
Interesting. Never heard of this before. Some more info here: https://en.wikipedia.org/wiki/Carbonado

2018-Sep-11, 09:05 PM
I'd never heard of it either, quite interesting.

There's a town of Carbonado in Pierce, County, Washington. It's less than 20 miles from Black Diamond. Both former coal mining towns, unsurprisingly.

2018-Sep-11, 10:36 PM
I wouldn't say they are 'apparently from space'. I'd say the provenance of carbonado diamonds is as yet unclear. They may well form through terrestrial processes as this (https://pubs.geoscienceworld.org/gsa/geosphere/article/9/5/1336/132672/new-textural-evidence-on-the-origin-of-carbonado) article suggests (suggests, not concludes).

2018-Sep-26, 12:36 AM
Thanks for the link. I have got a printout of it and it gives a great insight into the use of modern equipment in investigating stuff! The conclusion does not completely rule the origin of carbonado from "out there". And a referance seems pretty solid this is the source.

Roger E. Moore
2018-Sep-26, 04:45 PM
An extraterrestrial origin seems to have been ruled out in favor of a mantle origin. These are the two most recent arXiv papers on the topic that I could find.


3D Textural and Geochemical Analyses on Carbonado Diamond: Insights from Pores and the Minerals within Them

Eckley, S. A.; Ketcham, R. A. (12/2017)

Carbonado is an enigmatic variety of polycrystalline diamond found only in placer deposits and Proterozoic metaconglomerates in Brazil and the Central African Republic with unknown primary origin. These highly porous black nodules possess a narrow range of isotopically light carbon (delta13C -31 to -24 0/00), a primarily crustal inclusion suite unusually enriched in REEs and actinides filling the pore spaces, a crystallization age from 2.6 to 3.8 Ga, and other atypical features which have led to a variety of formation theories from extra-solar to deep mantle. We have completed the first multi-sample 3D textural analysis on nine carbonados using high resolution X-ray CT (XCT), with follow-up geochemical work. We have documented a variety of textures in both pore structure and mineralogy within pores. All pore textures feature a preferred orientation. Spatial coherence in pore fillings in some specimens suggest that secondary minerals formed by in-situ breakdown of primary inclusion phases. This, combined with the presence of pseudomorphs, support the hypothesis that elements comprising the secondary minerals within the pore spaces are actually primary. SEM-EDS analysis of one carbonado's exterior revealed the presence of zircon; XCT analysis of the complete volume indicates zircon is present only on the exterior of that specimen, but may be interior to others. Anticipated follow-up work will include LA-ICP-MS U-Pb dating and REE analysis of the zircon, and step-leaching and ICP analysis of some specimens. Periodic XCT imaging will allow us to trace leaching progress and effectiveness. To provide further context for our observed pore fabrics, we also analyzed a framesite, a less porous polycrystalline diamond found in kimberlites thought to crystallize shortly before eruption. Both diamond varieties have bladed/elongated pores forming a foliation with a moderate lineation. The similarity in fabrics suggests a similar process could have formed both carbonados and framesites. These data can shed light on the origin and constrain the age of carbonado, which may have far-reaching implications on the timing, origin, and mobility of light-carbon fluids in the mantle, early Earth's redox conditions, and the nature of a crystallization environment that can concentrate highly incompatible elements.



Carbonado revisited: Insights from neutron diffraction, high resolution orientation mapping and numerical simulations

Piazolo, Sandra; Kaminsky, Felix V.; Trimby, Patrick; Evans, Lynn; Luzin, V. (11/2016)

One of the most controversial diamond types is carbonado, as its origin and geological history are still under debate. Here, we investigate selected carbonado samples using neutron diffraction and high resolution orientation mapping in combination with numerical simulations. Neutron diffraction analyses show that fine grained carbonado samples exhibit a distinct lack of crystallographic preferred orientation. Quantitative crystallographic orientation analyses performed on transmission electron microscope (TEM) sections reveal that the 2-10 mum grains exhibit locally significant internal deformation. Such features are consistent with crystal plastic deformation of a grain aggregate that initially formed by rapid nucleation, characterized by a high number of nucleation sites and no crystallographic preferred orientation. Crystal plastic deformation resulted in high stress heterogeneities close to grain boundaries, even at low bulk strains, inducing a high degree of lattice distortion without significant grain size reduction and the development of a crystallographic preferred orientation. Observed differences in the character of the grain boundary network and internal deformation structures can be explained by significant post-deformation annealing occurring to variable degrees in the carbonado samples. Differences in intensity of crystal bending and subgrain boundary sharpness can be explained by dislocation annihilation and rearrangement, respectively. During annealing grain energy is reduced resulting in distinct changes to the grain boundary geometry. Grain scale numerical modelling shows that anisotropic grain growth, where grain boundary energy is determined by the orientation of a boundary segment relative to the crystallographic orientation of adjacent grains results in straight boundary segments with abrupt changes in orientation even if the boundary is occurring between two triple junctions forming a "zigzag" pattern. In addition, in diamond anisotropic grain growth results in triple junctions that rarely show 120 angles. Our results support the interpretation that carbonados may have undergone at least 2 or 3 stages of development with rapid nucleation, crystal plastic deformation to low strains and variable degrees of post-deformation annealing. Such a history is commonly observed in Earth's crustal or mantle rocks. Hence, for carbonados it is not necessary to invoke an extraordinary and/or extraterrestrial origin and history. The combination of methods utilized here, promises to help advance our understanding of diamond and diamond aggregates in the future.

2018-Sep-26, 11:13 PM
An extraterrestrial origin seems to have been ruled out in favor of a mantle origin. These are the two most recent arXiv papers on the topic that I could find.


3D Textural and Geochemical Analyses on Carbonado Diamond: Insights from Pores and the Minerals within Them.

Your first one is the article I linked to above. It certainly did not rule out extra-terrestrial origin.

2018-Sep-29, 07:31 AM
All good stuff but to me it is the overall fact about Carbonado, its extreme rareness and placement that indicates a space origin.