4. The sample shown below contains minerals such as calcium-rich plagioclase, pyroxene, amphiboleand 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 characteristicsthat we also need to take into account. Compare the rocks on the left with the corresponding rocks onthe right. Given that the composition of each pair of rocks is nearly identical, what else could accountfor the difference in appearance between the pairs of rocks?Vs.OJ Merck 2002Vs. Igneous Rock TexturesIgneous rock classification is based on both the mineral composition as well as the size of the mineralsor texture of the igneous rock. Why do we see differences in the sizes of mineral crystals?As molten lava or magma cools to form igneous rocks, the atoms in the lava or magma find their place inthe crystalline structure of a mineral and the minerals grow as the magma/lava solidifies.You are going to mimic this process using pennies. Find a handful of pennies or other small stackableobject (~20 should work). Scatter the pennies in front of you. The scattered pennies represent atomsthat are in molten lava or magma. A column of neatly stacked pennies heads up represents a mineralcrystal.6. In this first scenario, the molten rock is cooling fast and you only have 2 seconds to form thelargest 'mineral' that you can by stacking the pennies heads up. Use the timer on your cellphone to record the time while you stack your minerals.a.How many pennies did you stack in 2 seconds?b. Repeat this process but this time the molten rock is cooling slowing and you now have10 seconds to form the largest mineral that you can. Record the number of pennies thatyou stacked in 10 seconds.С.Under which condition do you think larger mineral crystals will form?Let's think about a scenario where the lava cools so quickly that you don't have time to stack anypennies. Would you form any minerals? Remember that all minerals have a set crystalline structure. Ifthe atoms don't have time to form a crystalline structure you end up with glass. Obsidian (shownbelow) is an example of an igneous rock that formed in this manner.

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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?