Elemental Compositions of Major Silicic Phases in Chondrules of Unequilibrated Chondritic Meteorites

Elemental compositions of olivine, low‐Ca pyroxene and mesostasis in chondrules from type‐3 ordinary chondrites (OC), CV3, CO3, CM2 and EH3 chondrites were compiled in a search for mineral compositional differences among chondrules of different chondrite groups. Such differences are demonstrated. A few elements occur in silicic phases in amounts proportional to their bulk chondrule concentrations: e.g., Mn in OC chondrules, Ti in CV chondrules, Cr in EH chondrules. However, OC chondrules have higher bulk Cr than CM‐CO chondrules, higher Cr in mesostasis, but lower Cr in olivine and low‐Ca pyroxene. The higher oxidation state of OC chondrules implies that Cr is more likely to be trivalent, and thus, less likely to enter the olivine crystal structure and more likely to concentrate in pyroxene and mesostasis. CV and OC chondrules have similar high bulk Fe and mesostasis Fe, but OC chondrules have much more FeO in olivine and low‐Ca pyroxene. The remaining Fe in CV chondrules is reduced and occurs as metal blebs in the mesostasis. Relative to OC chondrules, EH chondrules have lower bulk Ca, lower Ca in pyroxene and mesostasis, but higher (by a factor of 2) Ca in olivine. EH chondrules may have been incompletely melted, preserving relict refractory lithophile‐rich olivine nuclei. OC chondrules are richer than EH chondrules in FeO; they have a lower melting temperature and may have been more completely melted during chondrule formation.