Comparative Study of Minerals and Textural Constituent of Tourmalinated Pegmatite from Part of North Central and Southwestern Nigeria

Abstract

Six samples of tourmalinated pegmatite were collected from quarry sites at Oro (T1),Oke AsaIjero (T2),Komu 1(T3), Komu 2(T4),Ofiki (T5),Oke KusaIjero (T6).The rock samples labeled T1, T2, T3, T4, T5, T6 were reduced to 30microns thickness using diamond-coated cutting wheel. The sections were set in epoxy resin with different grades of abrasives having been polished to a 1-micron diamond paste finish. The mineral content and the textural features of the slides were studied under the microscope at x80 magnification under both crossed and plane polars.All the samples except Oke Kusa, IjeroEkiti (T6) show fragments of tourmaline in cordierite groundmass. Quartz, Microcline and Feldspars are in association with the tourmaline at Oke Kusa, Ijero and the groundmass is more of alkali feldspar. Cordierite is a dark blue mineral occurring chiefly in metamorphic rocks. It consists of an aluminosilicate of magnesium and iron, and could also occur as a dichroic gem variety and is mostly Mg rich. The presence of cordierite is however rare in igneous rocks, and might have resulted from the assimilation of aluminous sediments.  All texture is fragmental and porphyritic with prominent fracture except in Oke Asa (T2), Komu 2 (T4) and Ofiki (T5) where the fragments majorly exhibit tourmaline crystals of subhedral to euhedral form due to order of crystallization during magmatic activities.