School of Environmental Sciences Photomicrographs - igneous rocks Click on an image to enlarge it and see a brief explanation The six images below show examples of mafic igneous rocks. The essential minerals in these rocks are plagiolase feldspar and pyroxene.  (Olivine is another ferromagnesian mineral which may be found in these rocks)  In these thin sections you should be able to identify fine, medium and coarse crystal sizes, equigranular textures and porphyritic textures. The eight images below show examples of intermediate igneous rocks.  Essential minerals in these rocks are plagioclase feldspar and alkali feldspar. (Other minerals which may be in these rocks are biotite, pyroxene and amphibole) The first four images show coarsely crystalline rocks and you should be able to identify the feldspars and the different ferromagnian minerals. The next four images show another intermediate igneous rock named trachye. For these thin sections check that you can identify porphyritic texture, phenocrysts and flow alignment of feldspar phencrysts. The following images show three examples of silicic igneous rocks.  Essential minerals in these rocks are plagioclase feldspar, alkali feldspar and quartz. (Other minerals which may be in these rocks are biotite, muscovite and amphibole) For each of these thin sections try to identify the crystal sizes, minerals and rock textures shown. The essential minerals in the ultramafic igneous rocks are pyroxene and/or olivine. The images below show the ultramafic rock named picrite.