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Rocks: Rocks are a composed of one or more minerals. A rock can be made up of only one mineral or, as shown in the figure, a rock can be made up of a number of different minerals. So, rocks are composed of one or more minerals and minerals are composed of one or more elements. Previous Item: Why should we study rocks? Go Up: Learn About Rocks
Let's review. Igneous rocks are rocks made from the cooling and solidifying of molten rock. There are two categories of igneous rocks. Volcanic rocks are rocks formed when lava cools and solidifies on the earth's surface. Volcanic rocks are also known as 'extrusive igneous rocks' because they form from the 'extrusion,' or eruption, of lava from a volcano.