  Enstatite chondrites and aubrites are meteorites that show the closest
similarities to the Earth in many isotope systems that undergo mass-independent
and mass-dependent isotope fractionations. Due to the analytical challenges to
obtain high-precision K isotopic compositions in the past, potential
differences in K isotopic compositions between enstatite meteorites and the
Earth remained uncertain. We report the first high-precision K isotopic
compositions of eight enstatite chondrites and four aubrites and find that
there is a significant variation of K isotopic compositions among enstatite
meteorites (from -2.34 permil to -0.18 permil). However, K isotopic
compositions of nearly all enstatite meteorites scatter around the Bulk
Silicate Earth (BSE) value. The average K isotopic composition of the eight
enstatite chondrites (-0.47 +/- 0.57 permil) is indistinguishable from the BSE
value (-0.48 +/- 0.03 permil), thus further corroborating the isotopic
similarity between Earth' building blocks and enstatite meteorite precursors.
We found no correlation of K isotopic compositions with the chemical groups,
petrological types, shock degrees, and terrestrial weathering conditions;
however, the variation of K isotopes among enstatite meteorite can be
attributed to the parent body processing. Our sample of the main group aubrite
MIL 13004 is exceptional and has an extremely light K isotopic composition
(delta 41K= -2.34 +/- 0.12 permil). We attribute this unique K isotopic feature
to the presence of abundant djerfisherite inclusions in our sample because this
K-bearing sulfide mineral is predicted to be enriched in 39K during equilibrium
exchange with silicates.
