| Summary: | Potassium sulfide KFeS2 (hanswilkeite) has been identified in polymineralic inclusions in a diamond from the Udachnaya kimberlite pipe (Siberian craton, Yakutia). This is the second occurrence of hanswilkeite in nature and the first one in mantle-derived samples. Sulfide KFeS2 is monoclinic, the space group—C 2/c. Its crystal structure consists of chains with K in the interstices. The tetrahedra are centered by iron ions and linked by edges, thus forming chains of [FeS2] frameworks. The strongest lines of the electron diffraction powder pattern are 7.05 Å—(200); 5.34 Å (02¯0); and 3.05 Å (22¯0), and the angles between directions are <22¯0/02¯0>—60° and <22¯0/200>—30°. KFeS2 has been found as a discrete phase within polymineralic inclusions consisting of apatite, ilmenite, chondrodite, phlogopite, dolomite, and a fluid phase. The data obtained from the composition of the hanswilkeite (KFeS2) inclusion and other rare minerals (chondrodite, Mg-apatite, Cr-ilmenite) in primary inclusions in a diamond from the Udachnaya kimberlite testify to the important role of metasomatic processes in diamond formation.
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