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The isotopic composition and origins of silicon nitride from ordinary and enstatite chondrites
Author(s) -
Russell S. S.,
Lee M. R.,
Arden J. W.,
Pillinger C. T.
Publication year - 1995
Publication title -
meteoritics
Language(s) - English
Resource type - Journals
eISSN - 1945-5100
pISSN - 0026-1114
DOI - 10.1111/j.1945-5100.1995.tb01143.x
Subject(s) - enstatite , chondrite , chondrule , geology , geochemistry , astrobiology , silicon , meteorite , mineralogy , materials science , metallurgy , physics
— The N‐isotopic composition of acid‐resistant residues of three low petrologic type ordinary chondrites (Adrar 003, LL3.2; Inman, L3.4; Tieschitz, H3.6) and an enstatite chondrite (Indarch, EH4) have been measured by static mass spectrometry. All of these samples have been shown by transmission electron microscopy (TEM) to contain silicon nitride (Si 3 N 4 ), and no other nitrides were detected in any of the residues (Lee et al. , 1995). Stepped combustion has demonstrated the presence of at least two components with low C/N ratios, which have been interpreted as Si 3 N 4 . The most abundant component, common to all the meteorites studied, released during combustion at temperatures >1150 °C, may have formed during metamorphism of the meteorite's parent body. In addition, the ordinary chondrites Tieschitz and Inman show evidence for a second component of Si 3 N 4 that is less stable to combustion than the first and is enriched in 15 N. The unusual N‐isotope signature suggests that this second type of Si 3 N 4 may constitute a new type of interstellar grain. A comparison of the isotope and microscope data suggests that the >1150 °C component can be related to nierite (α‐Si 3 N 4 ) and the less stable component to β‐Si 3 N 4 .