REGULAR INTERGROWTHS OF MINERALS IN PEGMATITES FROM THE IL'MENY MOUNTAINS

Abstract

This paper summarizes the data on oriented intergrowths of minerals in pegmatites of the Il’meny Mountains. Two-feldspar, two-mica, biotite-amphibole, biotite-pyroxene, and pyroxene-amphibole intergrowths have been revealed in syenitic and miaskitic pegmatites. The orientation of exsolution products has been studied in sunstone (aventurine) and moonstone feldspars, nepheline, and cancrinite. Corundum-biotite-feldspar and two-mica intergrowths and exsolution lamellae occur in stellate corundum from corundum-feldspar veins. Syntactic intergrowths of various amphiboles and chlorites have been detected in pegmatoid ultramafic rocks. Regular quartz-feldspar (graphic) and two-feldspar intergrowths are typical of granitic pegmatites. Two-mica, columbite-samarskite, columbite-ilmenorutile, zircon-xenotime, cassiterite-ilmenorutile, cassiterite-ixiolite, cassiterite-tantalite, tantalite-stibiotantalite, fergusonite-columbite, pyrochlore-fergusonite, and beryl-cordierite intergrowths have been found in granitic pegmatites as well. New intergrowth laws have been established for many pairs of minerals.