  Low-iron, manganese-enriched (LIME) olivine grains are found in cometary
samples returned by the Stardust mission to comet 81P/Wild 2. Similar grains
are found in primitive meteoritic clasts and unequilibrated meteorite matrix.
LIME olivine is thermodynamically stable in a vapor of solar composition at
high temperature at total pressures of a millibar to a microbar, but enrichment
of solar composition vapor in a dust of chondritic composition causes the
FeO/MnO ratio of olivine to increase. The compositions of LIME olivines in
primitive materials indicate oxygen fugacities close to that of a very reducing
vapor of solar composition. The compositional zoning of LIME olivines in
amoeboid olivine aggregates is consistent with equilibration with nebular vapor
in the stability field of olivine, without reequilibration at lower
temperatures. A similar history is likely for LIME olivines found in comet
samples and in interplanetary dust particles. LIME olivine is not likely to
persist in nebular conditions in which silicate liquids are stable.
