TY - JOUR
T1 - Fine-grained-rim mineralogy of the Cold Bokkeveld CM chondrite
AU - Zega, Thomas J.
AU - Buseck, P R
N1 - Funding Information:
We thank Carleton Moore and the Center for Meteorite Studies for providing the sample of Cold Bokkeveld, and we thank Jim Clark and John Wheatley for EMPA and TEM assistance, respectively. We thank István Dódony for the insight that he provided on serpentine structures, and we thank Laurence A. J. Garvie, Craig L. Johnson, Hiromi Konishi, and John W. Moreau for discussions regarding TEM and mineralogy. We thank David R. Bell for discussions of compositional data and Xin Hua and Dante S. Lauretta for sharing their knowledge of cosmochemistry and for their initial editing of the manuscript. A. Bischoff, A. Brearley, and F. Brenker provided constructive reviews that greatly improved the manuscript. This work was supported in part by NASA grant NAG5-9352, a NASA Space Grant Fellowship, Arizona Mining and Mineral Museum Scholarship, and Sigma Xi grant-in-aid of research.
PY - 2003/5/1
Y1 - 2003/5/1
N2 - A chrysotile-like phase, cronstedtite, polygonal serpentine, pentlandite, and finely intergrown tochilinite comprise the fine-grained rim (FGR) mineralogy of the Cold Bokkeveld CM chondrite. Transmission electron microscope images combined with compositional data indicate reaction among cronstedtite, the chrysotile-like phase, and polygonal serpentine. The Mg/(Mg+Fe) ratios of the cronstedtite are higher than those reported for the less altered Murchison CM chondrite. Cronstedtite grains exhibit layer separations, particularly at their boundaries. The FGRs surround different chondrule types but have similar bulk compositions and mineralogy. Ca is depleted in the FGRs relative to the bulk CM chondrite. The FGRs display non-uniform thicknesses, especially where they coat embayed chondrule areas, and they exhibit grain-size coarsening outward from the chondrules they enclose. FGR formation in Cold Bokkeveld is most plausibly explained by multiple accretionary episodes during which progressively coarser dust was deposited onto chondrules, presumably in the solar nebula. The compositional and mineralogic data are consistent with aqueous alteration on the parent body.
AB - A chrysotile-like phase, cronstedtite, polygonal serpentine, pentlandite, and finely intergrown tochilinite comprise the fine-grained rim (FGR) mineralogy of the Cold Bokkeveld CM chondrite. Transmission electron microscope images combined with compositional data indicate reaction among cronstedtite, the chrysotile-like phase, and polygonal serpentine. The Mg/(Mg+Fe) ratios of the cronstedtite are higher than those reported for the less altered Murchison CM chondrite. Cronstedtite grains exhibit layer separations, particularly at their boundaries. The FGRs surround different chondrule types but have similar bulk compositions and mineralogy. Ca is depleted in the FGRs relative to the bulk CM chondrite. The FGRs display non-uniform thicknesses, especially where they coat embayed chondrule areas, and they exhibit grain-size coarsening outward from the chondrules they enclose. FGR formation in Cold Bokkeveld is most plausibly explained by multiple accretionary episodes during which progressively coarser dust was deposited onto chondrules, presumably in the solar nebula. The compositional and mineralogic data are consistent with aqueous alteration on the parent body.
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U2 - 10.1016/S0016-7037(02)01172-9
DO - 10.1016/S0016-7037(02)01172-9
M3 - Article
AN - SCOPUS:0038708331
SN - 0016-7037
VL - 67
SP - 1711
EP - 1721
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 9
ER -