Zoning in steenstrupine-(Ce) from the Ilímaussaq alkaline complex, South Greenland: a review and discussion

Abstract

Most crystals of steenstrupine are metamict, but some are crystalline throughout or in thin marginal zones parallel to the crystal faces of metamict crystals. The anisotropic parts of the crystals have lower contents of U and Th than the interior isotropic parts. Some features, such as high contents of Na in the anisotropic steenstrupine, favour formation of the zonation as a result of crystallisation in a medium in which decreasing amounts of U and Th were available during the last stages of growth of the crystals. One reason for this could be the fixation of U and Th in interstitial pigmentary material. Another feature, the fact that steenstrupine adjacent to fractures penetrating the crystals from the surface is anisotropic, indicates that leaching and recrystallisation may also play a role in the transformation of parts of metamict steenstrupine into an anisotropic phase.