Let’s start with a basic question: what is a rock? All rocks are made up of minerals and are defined as naturally occurring, nonliving, firm, and coherent masses of solid matter. The different ways that rocks form, break down, and reform is known as the rock cycle. Rocks that form from cooling magma or lava are known as igneous rocks. The composition of the magma, how it travels to the earth’s surface, and how quickly it cools will determine the characteristics of igneous rocks, which includes grain size, crystal shape, mineral content, and color. Examples of different igneous rocks are pumice, basalt, granite, and obsidian.
Sedimentary rocks are different because these types form near the earth’s surface where sediments eroded from igneous rocks are compacted on land, in river beds and lakes, or marine environments. They are then cemented in layers known as strata and are easily identified in nature because they will break along their layers. Another feature that makes them different is the fact that the vast majority of fossils are found in sedimentary rocks. Examples of sedimentary rocks are shale, limestone, and sandstone.
A metamorphic rock forms when an igneous or sedimentary rock is subjected to extreme heat and pressure and undergoes a dramatic change. The orientation and alignment of the crystals and the size of the grains change to form new rock. Different types of metamorphic rocks form at different temperatures and pressure, but if temperatures become too high and the rock melts turning back to magma, then igneous rock will form. Examples of metamorphic rock are slate, schist, and gneiss.
Still have questions about the rock cycle? Check out this informative and amusing video explaining it all!