Abstract:
Kosmochlor was found in these coastal sediments while sluicing for diamonds in Quaternary sediments of this region; the grains are emerald-green and as large as 0.17 x 0.15 x 0.15 mm. EPMA gave SiO2 52.31, TiO2 0.05, Al2O3 1.86, Cr2O3 25.57, FeO 1.29, MnO 0.01, MgO 2.79, CaO 4.33, Na2O 11.73, V2O5 0.10, = 100.04; this is a similar composition to that of kosmochlor in meteorites. The grains of kosmochlor contain microveinlets with Cr-diopside, similar to pyroxenes associated with diamonds in kimberlite, indicating P as high as 25 kbar, at relatively low T (800– 850°C). A possible source of the Tersky kosmochlor could be the deep-seated xenoliths from kimberlite and alkaline-ultramafic explosive pipes of Arkhangelsky and/or Kola region.
