RMZ – MATERIALI IN GEOOKOLJE

354 Akinola, O. O., Talabi, A. O.Figure 4. Photomicrograph of migmatite gneiss in transmited light showing crosshatchedtwinned microcline (M), large plates of biotite (B), fine grained quartz crystals(Q) and muscovite (Mu)Calc-gneiss is mainly composed of calcite,quartz with muscovite. Most of theminerals show evidence of strain andare altered. Calcite, quartz and muscoviteare the dominant minerals accountingfor 90 % of the modal composition.Ferromagnesian minerals like olivine,pyroxene and hornblende dominate themodal composition of epidiorite (Figure5). Quartz, muscovite, hornblendeand accessory opaque minerals dominatethe composition of biotite schist.Quartz occurs as small, colourless andsometimes cloudy xenomorphic crystals.Accessory zircon occurs as shortidiomorphic crystals while the opaqueminerals are few but existing as scatteredeuhedral grains (Figure 6). Biotiteoccurs in dominant amounts andforms the major groundmass minerals.In quartzite, quartz occurs as granoblasticand unaltered euhedral crystalswith well-defined outlines. It exhibitsweak birefringence, low relief withwavy extinction. However, some of thequartz grains appear cloudy.Muscoviteform supporting minerals as they occupyintergranular spaces of interlockingquartz crystals and sometimes occuras colourless elongated plates. In granite,the feldspars are large, well-formedcrystals of albite while quartz occurs asirregular masses of colourless and unalteredgrains.RMZ-M&G 2012, 59