LAUSR

Abstract Roaldite (Fe4N) is one of the few nitride minerals found in meteorites. Their nitrogen (N) isotopic signatures carry important information for understanding the early N cycle in the proto-solar nebula. However, the lack of knowledge on the N isotopic effects from nitride formation to its survival from frictional heating during landing impedes the interpretation and application of N isotope compositions of nitride minerals in meteorites. Here, we carried out laboratory experiments under a recently proposed roaldite forming condition, i.e., NH3 (as starting N source) reacting with metallic Fe at medium temperatures. We observed Fe4N formation over a large range of temperatures from 300 °C to 700 °C. The formation of Fe4N was associated with equilibrium N isotope fractionations with αFe4N-NH3 values of 0.9907 (±0.0004) at 300 °C and 0.9936 (±0.0004) at 500 °C, respectively. In the experimental pressure conditions (initial PNH3 = 3.9-6.4 bar, PTotal 300‰. Thus, great caution is needed when using N isotope composition of roaldite (and probably other nitride minerals as well) to trace source information.