4. The sample shown below contains minerals such as calcium-rich plagioclase, pyroxene, amphibole and olivine. How would you classify the composition of the rock below? 5. While composition plays a big role in the classification of igneous rocks, there are other characteristics that we also need to take into account. Compare the rocks on the left with the corresponding rocks on the right. Given that the composition of each pair of rocks is nearly identical, what else could account for the difference in appearance between the pairs of rocks? Vs. OJ Merck 2002 Vs.