Olivine in a coesite-bearing eclogite from the Udachnaya kimberlite pipe

Olivine (high-Fe forsterite; Fo# 69-76) and associated minerals have been studied in a coesite-bearing diamon-diferous eclogite from the Udachnaya-East kimberlite pipe. Olivine was identified in the rock interstices together with K‑feldspar, sodalite, phlogopite and djerfisherite. The composition of individual olivine grains varies within the xenolith and is characterized by a consistent presence of P 2 O 5 , MnO, CaO и Al 2 O 3 . The coexistence of olivine and coesite is uncommon for mantle xenoliths. The occurrence of olivine and K, Na, Сl-bearing minerals in the studied sample is suggested to have been caused by the interaction of the eclogite with a protokimberlitic melt enriched in alkali components and chlorine.