Exam 2 study guide igneous environments, volcanism, sedimentary rocks. Chapter 3: igneous environments: determine the composition (felsic, intermediate, or mafic) and texture (aphanitic, porphyritic, or phaneritic) of an example igneous rock. Aphanitic: an igneous texture characterized by crystals that are too small to see with the naked eye. Porphyritic: an igneous texture in which some of the crystals are distinctively larger than the rest. Phaneritic: a rock texture in which the individual crystals or grains are visible to the naked eye: describe the characteristics (composition and texture) of granite, rhyolite, diorite, andesite, gabbro and basalt. Identify these six rocks if given a sample. Mafic: gabbro(intrusive) is very dark in color due to its mafic composition. It has larger crystals and rougher texture than basalt; basalt(extrusive) is almost black in color with a little bit of a green sheen to it depending on how much olivine it contains.