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Proposed structures for poorly characterized phases in C2M carbonaceous chondrite meteorites


Recent investigations of meteorite matrices using analytical electron microscopy and high-resolution transmission electron microscopy (HRTEM) have provided data on the structure and chemistry of poorly characterized phases (PCP)1. We suggest here that 10 Å PCP, a dominant matrix variety, has a structure equivalent to iron-rich tochilinite [6Fe0.9S 5(Fe, Mg) (OH)2] which consists of coherently interstratified mackinawite and brucite sheets2. In addition, we propose that 17 Å PCP, previously described as an SBB-type mixed-layer structure3, is a commensurate intergrowth of serpentine and tochilinite layers. A wide range of cation substitutions is possible within both tochilinite and serpentine–tochilinite structural types. We suggest that various forms of PCP observed in carbonaceous chondrites4,5are intergrowths of tochilinite, serpentine, serpentine–tochilinite and/or valleriite-type minerals6.

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Mackinnon, I., Zolensky, M. Proposed structures for poorly characterized phases in C2M carbonaceous chondrite meteorites. Nature 309, 240–242 (1984).

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