FAYALITIC OLIVINE IN MATRIX OF THE KRYMKA LL3.1 CHONDRITE - VAPOR-SOLID GROWTH IN THE SOLAR NEBULA

Fayalitic olivine (Fa(54-94)) is a ubiquitous component in the matrix of Krymka (LL3.1) as well as in other highly unequilibrated chondrites (ordinary and carbonaceous). In Krymka, the fayalitic olivine has an unusual anisotropic platy morphology that occurs in at least five type s of textural settings that can be characterized as: (1) isolated plat elets, (2) clusters of platelets, (3) euhedral to subhedral crystals, (4) overgrowths of platelets on forsteritic olivine, and (5) fluffy (p orous) aggregates. From transmission electron microscope (TEM) investi gation, the direction of elongation of the platy olivine overgrowths o n forsteritic olivine substrates is along the c axis and in most cases it corresponds with the c axis of the substrate olivine, which sugges ts that the fayalitic olivine grew in this unusual morphology and is n ot a replacement product of pre-existing material. The fayalitic olivi ne in the matrix of Krymka is compositionally similar to olivine with platy morphology in the matrix of some CV3 chondrites and both have si milar Fe/Mn ratios, but important morphological differences indicate t hat their relationship needs to be explored further. Textural and comp ositional data indicate that the fayalitic olivine in the matrix of Kr ymka, as well as in some other unequilibrated ordinary chondrites, for med prior to final lithification of the meteorite and probably prior t o parent body accretion. We find that formation of the fayalitic olivi ne by vapor-solid growth provides the best explanation for our observa tions and data and is the only feasible mechanism for the formation of fayalitic olivine in the matrix of Krymka. We propose that the fayali tic olivine formed by vaporization and recondensation of olivine rich- dust, during a period of enhanced dust/gas ratio in the nebula.