Direct Evidence of Sulfidation of Metallic Grain in Chondrites.

A large number of fractures dividing the troilite (FeS) into two distinct layers around metallic grains were observed in chondrite samples (ALH-764 and Y-791717) for the first time in the present study.A similar fracture was successfully reproduced in experiments with iron-meteorite sulfidation.The fracture texture shows that the troilite was formed by reaction between metallic grains mainly composed of Fe-Ni alloy and S-rich gas.The thickness distribution of troilite in chondrites can be used as an indicator of the cooling history of the gas, and as a result, some important constraints can be determined for the formation of chondrites.