Partitioning of potassium between silicates and sulphide melts: Experiments relevant to the earth's core

Abstract

The partitioning of potassium between roedderite, K 2Mg 5Si 12O 30 and an FeFeS melt was investigated at temperatures about 40°C above the FeFeS eutectic. Roedderite was considered a prime candidate for one of the potassium-bearing phases in the primitive Earth because roedderite and merrihueite are the only two silicates containing essential potassium which have been identified in stony meteorites. A mean K 2S/FeS weight ratio of (3.340 ± 0.015) × 10 −3 was determined in these experiments; a K 2S FeS weight ratio of about 1.0 × 10 −2 would be sufficient to extract all potassium in a chondritic Earth into the core. Application of these results to a primitive chondritic Earth is discussed and it is concluded that extraction of most of the Earth's potassium into the FeFeS core would occur under the conditions in the early Earth.