Djerfisherite: Nebular Source of Refractory Potassium

TL;DR

This study derives an equation of state for djerfisherite, a potassium-bearing mineral in enstatite chondrites, to understand its formation conditions and implications for planetary volatile budgets.

Contribution

It provides a new EOS for djerfisherite and models its thermal stability and condensation in nebular environments, linking mineral formation to planetary composition.

Findings

Djerfisherite condenses above 1000 K in nebular dust.

Mineral assemblages match those in enstatite chondrites.

Results suggest implications for planetary volatile budgets.

Abstract

Djerfisherite is an important carrier of potassium in highly reduced enstatite chondrites, where it occurs in sub-round metal-sulfide nodules. These nodules were once free-floating objects in the protoplanetary nebula. Here, we analyze existing and new data to derive an equation of state (EOS) for djerfisherites of K_{6}(Cu,Fe,Ni)^{B} (Fe,Ni,Cu)^{C}_{24} S_{26}Cl structural formula. We use this EOS to calculate the thermal stability of djerfisherite coexisting in equilibrium with a cooling vapor of solar composition enriched in a dust analogous to anhydrous, chondritic interplanetary dust (C-IDP). We find that condensed mineral assemblages closely match those found in enstatite chondrites, with djerfisherite condensing above 1000 K in C-IDP dust enriched systems. Results may have implications for the volatile budgets of terrestrial planets, and the incorporation of K into early-formed, highly reduced, planetary cores. Previous work links enstatite chondrites to the planet Mercury, where the surface has a terrestrial K/Th ratio, high S/Si ratio, and very low FeO content. Mercury's accretion history may yield insights into Earth's.