Abelsonite – a chemofossil

Abelsonite

• Discovered only in 1969 (by the way the year of birth of the author of this blog) by Lawrence C. Trudell while he was exploring the Green River Formation (Utah, USA) for an oil shale project
• Named after Philip H. Abelson (1913–2004), a long-time editor of the journal Science, for his pioneering work in organic geochemistry
• Abelsonite is formed as a secondary mineral (and is one of the few organic minerals)  on oil shale surfaces by conversion of chlorophyll – therefore, it is called a chemofossil (a fossil that consists only of chemicals remaining from the decomposition of a living organism)
• Abelsonite is the only known naturally occurring crystalline porphyrin derivative
• Formula: NiC₃₁H₃₄N₄
• Space group: P-1 (No. 2)
• Crystal system: triclinic
• Crystal class: -1
• Lattice parameters: a = 8.4416 Å, b = 10.8919 Å, c = 7.2749, α = 90.465°, β =113.158°,  γ = 78.080°

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Picture: CC BY-SA 3.0 Thomas Witzke – http://tw.strahlen.org/fotoatlas1/abelsonite_foto.html

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Crystal structure (click on the picture to download the CIF):

• Ni: green, N: blue, C: gray, H: white
• Note: Although a single Ni porphyrin molecule does not possess -1 symmetry, matching ethyl groups at roughly opposite ends of the molecule enable orientational disorder, in which molecules can randomly adopt one of two different orientations while still stacking in the same manner. The aggregate of these two random orientations produces an overall symmetry of P-1.
• Reference: Crystal structure of abelsonite, the only known crystalline geoporphyrin
  Daniel R. Hummer, Bruce C. Noll, Robert M. Hazen, Robert T. Downs
  American Mineralogist (2017) 102 (5): 1129-1132.
  https://doi.org/10.2138/am-2017-5927

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